Both videos (Veritasium's video and Dave's analysis) are very interesting. But I still do not understand why we need wires in real life. From both your and Veritasium's video I understood *if* the energy would be transported along the wire with the speed of light it would take more time than if the energy takes the shortcut (direct path) from the battery to the bulb. His and your experiment show the bulb turns on faster than a "signal" could travel along the wire. So "why do we then even have to have a loop? Why are two separate parallel wires not sufficient to turn on the bulb?" If we need a circuit only because we need some current: use two separate circuits. One wire connecting plus and minus of a battery and another circuit with the light bulb. Both loops close to each other. Now if I would try this with a battery and a light bulb I am sure the wire in the battery loop would get pretty hot and the light bulb would not turn on. Or maybe it would be super dimmed. But if I set up a conventional circuit with battery and bulb in the same loop the bulb would shine brightly. Now, for very close distances, energy can be transmitted "contact-less" (as used in wireless charging of e.g. smart phones) with high efficiency. I think I even (partially) understand that some sort of dampening makes the wireless energy transfer over large distances inefficient, but not impossible (I think any radio wave is transporting energy). So for "large" distances (e.g. already just a few meters in a house) we need wires to transport the energy. We cannot use a small loop with a bulb at e.g. level 2 and an energy source at the ground level with another loop. We need to connect both with a wire in a loop. But why do we need the wires if the energy is not transported along the wire?
Thank you for this explanation. Two observations: 1) "Disingenuous"... Derek made a "clickbait" video and is smiling as dollars are transmitted into his bank account. 2) You address the crux of the controversy at 37:37 in your video... The power transferred at t=3x10^-9s is "naff all"... The bulb would not light... Derek lied. Again, thank you for making your response to a "scientist's" fake science video in which he works very hard to deceive. Next up: Veritasium demonstrates that smoking is good for you!
3 года назад+3
@@slowhornet4802 Wires are needed because they lead the electromagnetic waves where to go. If two wires go to the moon parallel to each other, one meter apart, then the bulb would be lit up one second after the switch turns on. Because the distance between the electric generator (battery) and the bulb would be a little more than one light second.
@ You should look up time domain reflectrometry, and see how transmission lines are modeled. You haven't described your scenario. Is the bulb on the moon at the end of the parallel wires (a balanced transmission line) with the battery on Earth? Then it will take about 1 second to light. Or are the bulb and battery each on the Earth, each connected to their own end of the wires, then the circuit is closed between the bulb and battery? In that case, the bulb gets current right away and a wave begins travelling down the transmission lines to the moon. How bright the bulb is depends on the resistance of the bulb versus the characteristic impedance of the wires. And it will take about 2 seconds for you to find out if the other end of the wires are short or open.
Its like everything else... you simplyfy to the most usefull system. Calculating magnet flux inna Electric cricut is pretty much impossible. But when doing magnetism you have to do it of cause.
As an electronic engineering student I had lectures about all of this, but I didn't really make the connection that power is always transmitted through the fields. I understood it at the special case of the space between capacitor electrodes, but never generalized that idea. Veritasium's video and your explanation to it flicked a switch in my brain. Thank you so much for that!
Well, fields carry energy, but the fields are generated by the moving charges .... its a question what is first, the chicken or the eggs .... claiming one or the other does something separately gives bad pictures ...
I'm a non engineer, but I want it to click in my brain, too. I'm gonna keep watching this vid and others. I just can't focus that hard, and there's some whoosing going on.
For his light bulb in a field idea to even work on pure field propagation you would need a tesla coil to create a high enough field strength at operating frequencies to light the bulb "wirelessly". You still need to take into account impedance, dielectric, conductivity, angular propagation, reflections, and you'll arrive at a speed of propagation and VA required to operate the circuit The simulation he performed as well assumes the capacitors have a static charge*(steady state) from T-0. if they were discharged you'd have to calculate the time constant in an LRC circuit based on the characteristic capacitance of the circuit.
So, basically, the energy will reach the bulb through 1 meter of space, by the means of capacitive coupling, way before the far ends of the wires start conducting?
Excellent analysis, Dave. I’m reminded of Physics and Chemistry classes at school: “So class, remember how we taught you about X last year? Well that’s not entirely true, so let’s look at what really happens.” And then a year or two later they do it again, and peel another layer from the onion. Makes complete sense as to fully understand the topic would just be too much, so we start with a simplistic explanation and slowly head towards the truth…
@@spot997haha - and the culmination of all: everything boils down to philosophy + spirituality (..or so) or,: matter or hardware don't exist - only consciousness, waves & software
Than again, introducing particles instead of waves and talking about this weird thing of particle-wave duality, which is not only hard to understand but also plainly wrong is the bane of physics. There are ONLY waves, there are NO particles. Those waves are sometimes so localized and symmetrical that we can approximate them with particles i.e. balls of marble, but that's NOT what's happening. Physics should ban teaching about particles and just focus on waves from the start. Then slowly expand the wave model into the full description based on fields. There's just no place for particles in modern physics curriculum as it gives the wrong impression to people as to how things are and work.
This was one of Veritasium's first videos that left me feeling like didn't really grasp what he was trying to explain. Your video helped me actually understand more about the concepts being discussed here. Cheers.
He left out well established concept like capacitance and inductance coupling between wires making the puzzle more mysterious than it really is. I speculate he (or his writer) left those out purposely.
at 13:07 the interviewee says: "People seem to think you are pumping electrons..." and Dave chuckles at the idea - "nobody thinks that". However, this belief is pervasive amongst non-engineers because this is what most of us were taught in physics at school. And, ironically, this belief is prevalent amongst astronomers and cosmologist, too, because they are constantly trying to explain the presence of magnetism in the cosmos (and our solar system) by gravitational spin and "remnants" - not attributing it to energy and electric flow because there is no evident wire to provide an electron "circuit"
I was smirking at that "nobody thinks that" aswell. Actually as far as i know this is actually what the vast majority of people think. "There is this electrical current thingy that flows out of the wall plug and makes my stuff work."
Exactly, this is what I learned in school. Simple as that. That needs to change is my idea, it doesn't make things very clear if you go any further than what you were taught and what's really the point then to learn it in a bad way?
Maybe most people think it but I think it's a fairly common exercise to calculate the speed of an electron in a circuit and find out its slow. The chain model he uses is actually fair too but you need to be aware that the speed of sound in the metal is more like the propagation of the signal than the movement of the chain (we learned of virtual "phonons" as the equivalent to photons then never used the term again).
I learned that elastic collisions between the electrons and the atoms in the conductor is the cause of resistance/impedance. I guess this is actually wrong? How does the field model explain resistance?
Something interesting I want to remark is when you said: "is nothing new for engineers" . I thought I knew about the basics of current (and I'm an electronic engineer) and honestly, during my time in the university, no teacher told me about the pointing vector (I remember a teacher mentioning it once, but just as a little mention, and honestly I am not blaming anyone) and seeing this to me is really new and honestly opened my mind on how do this world of electricity works. Excellent video Dave!
Indeed. The Real World(tm) works with real world considerations, not fancy, complicated, thought experiment math models. Stretch out a million miles of super conducting wire and _prove_ it's 1(m)/c. Two wires 1m apart have f*** all for capacitance. (I've never even seen an instrument capable of measuring such a low capacitance.) The power did not flow from the battery to the bulb through 1m of open space. It's flowing along the wires, or we wouldn't need the wires in the first place. If the battery has been connected for more than 1s, all of the wire has been "charged". Closing the switch at that point would, in theory, instantly allow power to flow. This is the "water pipe" equivalency -- once the pipes are filled, water can appear to flow miles away almost immediately. If that hose hasn't been primed, it's going to take awhile to flow. This is the kind of physics experiment I'd like to see! 2ls of super conductor is hard to come by. If we do this with fiber optics (light/photons) -- and we have, this field theory math nonsense goes away. If you have 1ls of fiber, nothing comes out until 1s after you fire a photon in the other side.
@@jfbeam Real world(TM) is too complicated to be able to usefully calculate the necessary stuff correctly. The way I remember an engineer decided to replace d/dx with a variable s and so his differential equations like you do your your normal equations. Mathematicians had a fit because it worked but there was no math to prove it true until Laplace.
I agree, my undergraduate degree in electronics glazed over a lot of critical theory under the guise of "you have to learn it yourself". It was disjointed and rather than focusing on the critical, fundamental theories they focused more on providing you with practical skills, which to be honest killed a lot of the joy in curiosity I had and I've been forced to learn and discover accidentally by myself, in my own time.
I'm a retired Director of Engineering with my field in Electronics. I love your videos. I especially like it when you destroy scammers like Solar Roadways. I worked for a small defense contractor and I'm very aware of SBR's. There are people who take advantage of people's ignorance of science, electronics, etc.
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, the better model is a dipole antenna model. See my explanation in the main thread.
I’m so sad to find out that solar roadways is bullshit. I don’t really know anything about electricity beyond what I have to know to run my amplifiers, but that video gave me so much hope for the future. Makes me mad to think that people were just pulling on heartstrings.
My main objection to the Veritasium video was the implication that the electrons don't really matter. They don't carry energy, and look at how slowly they're moving!?!?! No, it's the fields they generate that carry energy. Well sure, but those fields don't exist without the electrons and their ever so slow motion. I know that he never would actually say that outright because he knows it's not true, but he leaned really hard into a semantic argument that got close. It's like saying that people don't actually buy things in a shop, no, it's their money that buys things. Well yeah, that's true, it's the exchange of currency that allows for a purchase (in most cases these days anyway) but it's the people who bring the money to the shop. They're not separable.
Thanks for this comment, I'm no physicist, but have had some college level courses in electronics, electricity, X-rays, and passed the first 2 ham radio license tests, and his video threw me off of almost everything I understood about electromagnetism. This is the point I was grasping at, and it really seems like the two can't really be separated out from each other. The moving electrons generate the electromagnetic field, and without electrons there would be no field, and no power. Derrick showed the hosw/chain/wheel analogy which is a pretty good way to demonstrate how electricity works. I suppose the point of his video is that the chain is not representing electrons, but the en field. That means that the electrons would be represented by pulling the chain back and forth, and it seems that without the hands, the work isn't getting done.
@memyself I am not quite sure, but other science based channels state that the the magnetic field is intrinsically tied to the electronic field. These other videos state that they can't be separated, and just because the electrons themselves don't actually flow entirely through the wires like water molecules through a pipe, it is their change in state that results in the pulse of energy. It seems like it similar to a wave in a rope, we can hold one end and move it up and down to create a wave. The rope molecules don't actually travel down the rope to the end, where something may be happening due to the waves movement, but no one can argue that the wave is a result of a change in the rope's state. This is how it seems electrons are used to produce electricity, we charge the electrons on the wire, which causes a chain reaction in the adjacent electrons, creating a wave. In any case, from what I have gathered, the charge generated at 1m/c is due to magnetic induction from the battery side, similar to how a transformer or wireless charger works, only at a greater distance. This makes sense and matches the physics I learned about electricity. If you know of videos that explain something different happening, please post the links.
Most electrical engineers have a hard time graduating from DC to RFM microwave. In fact all of electromagnetism everywhere in the universe it's an AC phenomenon any DC electricity is simply electromagnetism where the frequency equals zero, so it is it is an extraordinarily isolated case. And to an extent the electrons and the fields are quite separable: just consider the entire radiation field of the sun which contains a practically infinite (but not infinite, simply integrate the Planck distribution) spectrum of frequencies propagating outward, some of it intercepted by the earth. Anybody on the earth can measure the intensity of the field at any given frequency...when so doing where is the electron?
@memyself I follow your explanation right up to the last where you say, "Current flow is not energy flow." Since current requires electrons to move and they can't move without an E-field, and once they do move, there is an M-field generated.
40:24 - Feynman showing that "the Poynting vector" is going into the wire: This is not the entire Poynting vector that represents the energy flow from source to load. That part that goes into the wire represents the losses in the conductor. We strive to have good conductors - the better the conductor, the smaller the electric field in the axial direction of the conductor and the smaller the component of the Poynting vector pointing into the wire. When integrating this component of the Poynting vector over the surface of the conductor, the result is I*I*R. There would be no voltage drop on a wire with zero resistance, so the electric field in axial direction would be zero as well and there would be no bit of the Poynting vector pointing into the wire. All the energy would remain in the field outside the wire.
Great comment! Yes, it's actually weird that from the basic stand point of conservation of energy, one can so casually keep saying that the Poynting vector, i.e energy flow (flux) is towards the wire (and keep assuming a lossless wire). Dave makes it seem like it has something to do with the energy flow along the wire. (or that's how I understood him) But how would the energy the propagate to the load if this is the only direction of the Poynting vector? Actually I think transmission line theory for this problem is even more complicated than just imagining it as two dipole antennas. Well .. if antenna theory is any easier to understand.. but intuitively you would see why the energy travels near instantly to the load -- because they are two dipole antennas next to each other.
i watched how powerlines were being repaired using a helicopter, and was given some explanation as to how this was possible without getting electrocuted. seems the electric field was diverted around the helicopter so that the cable could be repaired.
Pointing vector goes into the wire IF and only IF wire has resistive losses, otherwise the tangential electric field on the surface of the prefect conductor is zero.
Component of the pointing vector flowing into the wire is the resistive loss. The component of pointing vector along the wire is the one carrying the power to the load. The DC electric field inside the bulk of conductor is proportional to the resistive loss!
Most wires which I have encountered in the real world (I am a physicist by training) have resistive losses, even though I have made experiments at an electron synchronton with superconducting magnetic coils once.. but even there most cables were actually standard, resistive copper cables.
Very valuable pair of videos. Kudos to both Derek and EEVBlog for appealing to general audiences in order to explain the magic of electromagnetism but also to confirm to RF engineers what they've been doing for decades, which itself is a confirmation of the physics behind electromagnetism. The physics behind electromagnetism is lucidly and brilliantly explained in the textbook Electrodynamics by Melvin Schwartz first published in the late 60s. Basically the entire field of Electrodynamics rests upon a solid underpinning of Einstein's relativity and the fact the the Electromagnetic field is a 4D Invariant Tensor, not some combination of 3D vectors. In addition, ohms law is an approximation based on the assumptions made about the drift velocity of electrons. Well done
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, the better model is a dipole antenna model. See my explanation in the main thread.
The problem I had with the veritasium video was, that some real life problems (resistance) are waved away, but others (capacitance) are not but not mentioned - and this feels like it is deliberately misleading. Also Derek should have mentioned that the layout of the cables is very important. This way the correct answer depends on effects that he made me ignore with the introduction ("we have to simplify this")
He acts like many bad teachers do: He creates an environment where his specific statements are true and leaves out the factors he had to set up to make his statements true. BTW: I'm still curious why we need thicker wires for powerful applications if the power is not transmitted inside the cable anyway.
Have you ever taken a physics course? Problems are always simplified in order to focus on the principles of the subject at hand, especially in introductory courses. When, for example, you are first introduced to capacitors, you ignore edge effects. You don't use Jackson in a first-year physics course.
Imagine a different layout: a almost planar (X - Y) figure 8, crossing point distant 1m in the Z direction and the lines on the crossing plane in 90deg. The capacitance is minimal in this case and the battery and lamp will be 1m apart. If Derek is right, that the power is not transmitted over the cables, but over space (air), the lamp will turn on the same way, right? MAKE A F# EXPERIMENT! He could do it with relatively simple equipment, like an oscilloscope and differential probes. Very disappointed with Derek...
@@michaelsommers2356 yes, but normally you say what you simplify but pronounce the effects, that you are going to focus on... instead of mystifying them to "totally blow you mind"
30:00 It's actually an important fact, that initially it doesn't matter if the circuit is closed or not. If that made a difference it would enable faster than light information transmission, which in turn, would spin up Einstein to really high rpm in his grave.
What I wish there was more discussion of here (especially since it's something Derek got so into in the Slinky Drop series) is a difference between how quickly the information that the switch has closed gets to the light bulb, and how long it takes to actually light up a practical light bulb, and for how long it would stay lit, etc. Like, I can grok the information getting there, but how much power is in that brief spike Dave showed in the simulation? Not much, I should think. Enough to even light a red LED?!???
@@manojlds interesting question. Since the potential of the wire opposite the battery should initially be between the between those of the battery terminals the Poynting vector goes outwards in both directions during the first half second. That corresponds to the energy invested into charging those "capacitors" the two parallel wires on each side can be considered as. Another way to see it is as energy invested into building up the electromagnetic field between the two wires. There's an electric field between the wires due to the potential difference, and a magnetic field around each wire due to the current. At most that can expand outward from the battery/switch (let's keep them together) along the wire pairs with light speed at most (when/where air acts as a dielectric medium between the wires it's likely a little less). Another way to look at it is as a signal (like a step function) traveling along a wire pair, and where it has been through . When the electric field hits the end where the wires are short circuited that wave is reflected. This reflection of the wave at the ends where the wires meet depends on whether they are connected, and e.g. if there's a light bulb between them. See this for the difference between those resistances: ruclips.net/video/zrDxSM91Jcg/видео.html It'd be interesting to do a version of the experiment with just two rolls of twisted wire pair, like the one in the video. It's about at that point that I'd need to consult some physics books and maybe do some math to get beyond hand waving and really see what happens. I think the wave traveling back puts both wires on the same potential, effectively unloading the part of the capacitor behind it and the Poynting vector from the battery outwards is cancelled. This travels past the battery, the Poynting vector on the load side then doubled, as the other wire is then on the same potential as the terminal on the closed side. On the bulb side the impedance of the cable pair and the resistance of the bulb will probably be important, else we have some kind of reflection there too. If it is matched, then the bulb is lit with half voltage when the 1st wave arrives (1/2 s after the switch is turned) and with full voltage when the reflected wave arrives (1s later, so 3/2 s after the switch is turned). But I'm really guessing a bit here. I honestly also don't know how the thickness of the wires comes into play, because that affects the capacitance, inductance and impedance of the wire pairs. There are impedance calculators for twisted wire pairs, according to them wires with 1mm thickness would result in an impedance of about 1k Ohm. This (and the battery voltage) should determine the amount of initially outgoing current after flipping the switch (at that point the current can't be determined by the resistance of the light bulb at the far end. I'd also have to look into the "no resistance" thing. The dampening effect usually helps to make such systems well behaved. Maybe it's enough to assume an inner resistance of the battery (and of course the light bulb). Setting the whole system up without any resistance at all (just a closed loop) probably results in an oscillating system.
Einstein was covard and hypocryt.. He even try "exorcixm" at quantum entanglement.. We have confirmed Bosson.. Specialy his TAU what is confirmed fasther than light.. Is just opening another layer of physic onion.. If you cry after you remove skin.. You shut not be a coocker
My personal problem with Derek's analysis is that (as can be seen from your simulation), the "ON" state of the lamp lasts only a couple of miliseconds. I don't consider this to be actually "ON". Particularly in a video aimed at general public (i.e. not electrical engineers / physicists), no one would consider this to be ON. For something to be consodered ON in this context, it has to stay on (steady state). So, the answer is not 1/c. If the question was "when will you see a voltage spike across the lamp in the transient analysys of the circuit?", then the answer would be 1/c
What he doesn't bother to explain, is that it isn't just the fields close to the switch that are at play. After the switch is turned on, there is an immediate step in the voltage at the wire, which gets coupled to the other wire. But also, that step is moving toward the right over time, such that for the whole time that voltage step is moving to the right in the lower wire, it is coupling to the upper wire, and takes a while to get back to the light bulb. So the whole time the pulse is traveling to the right, there is energy being transferred to the upper wire. This continues until the pulse turns around at the end, returning on the upper wire. The result is that there is a (near) instantaneous low-level lighting of the bulb for one second, followed by a brightening at the one second point. At least, this is how it works if you use a random size of wire and a random light bulb. But because the pulse is losing energy as it propagates, if the wire (actually a transmission line) and the bulb are properly matched, you won't see a change in brightness because the pulse that had to travel the whole distance will be at the same level as the current that was induced as it traveled to the right.
@@BrightBlueJim Are you saying that if the transmission line had been perfectly matched to the light bulb in Dave's simulation, then the voltage and current would be constant after t=0 rather than instantly drop off? Is it even possible for the transmission line in Derek's hypothetical experiment to ever be matched to the light bulb?
@@ncmaothvez Yes, that's what I'm saying. Almost. There's still the 1/c delay that the pulse has due to the 1m spacing between the wires. and yes, after around 3ns, the light bulb goes on, and stays on at a constant brightness. At least, that was what I thought. Turns out I was still wrong, though. At first, I was thrown off by the 1m spacing, because I'm used to much smaller dimensions in transmission lines, so I thought that the impedance of the line would be very high. But then I "ran the numbers" and for a reasonable range of wire diameters, like 1mm to 10mm, the impedance is actually around 500 to 1000 ohms. Using an on-line calculator for transmission line impedance, because I'm lazy, I find that making a twin-line transmission line out of 2mm wire, we get an impedance of 828 Ohm. For a 120V light bulb to have a resistance of 828 ohms, it would have to pass (120V/828 Ohm =) 145 milliamps, which would make it a (0.145A * 120V =) 17.4W light bulb. This is close enough to the 16-17W of a typical "100W equivalent" bulb to work. But NOW I realize that there's still a problem: the transient solution to this problem - what happens when the switch is flipped - puts the transmission line's impedance in series with the bulb, which results in half the voltage being dropped across the transmission line and the other half across the bulb, which Derek alludes to in his video. BUT, the steady-state solution - what happens when the transient electric field has faded out because both wires eventuailly reach the same potential - drops nothing, due to the hypothetical zero-ohm wire, putting the full battery voltage across the bulb. So I was wrong about that - even perfectly matched, the bulb will come on at half-brightness for one second before it abruptly rises to full brightness as the initial switch-on pulse travels around the loop and reaches the bulb. I don't just know this from theory - I worked for six years in high-power microwave pulsed RADAR systems, which use a modulator that incorporates a set of inductors and capacitors to make an artificial transmission line that operates much like this circuit, and the amplitude of the pulse IS pretty close to constant over the time it takes a pulse to travel through the transmission line and back. So the transient solution isn't just a quick spike caused by the capacitance between the wires, but a pulse whose length is twice the time delay of the transmission line. Isn't electromagnetism fun?!
@@BrightBlueJim I've got to admit that my analog electronics theory knowledge doesn't reach very far beyond ohm's law and a crude understanding of transmission lines but I was still able to follow along in your explanation. Thanks for the reply! This got me curious, need to read a bit about transmission lines tomorrow when my brain is a bit more awake :) Yeah, I'd never have guessed the impedance would be as low as sub-1000 ohm's.
Exactly. This spike would happen even if the circuit is not closed. And we don't call that "ON". Yes, you generated 0.00...001A in it, but you don't need 2x300000km wire for that... The ON state means at least that you can differentiate the current from the case when the circuit is not closed. It would be still a low current, but also at least .5sec...
Thank you Dave, this video provided me the information that I felt was missing from the Veritasium's video. I've studied civil engineering, not electrical engr and also I have my amateur radio certificate so this helped me link the transmission line theory into all of this. I've come to realize that there was something missing from my understanding of how all this works, I guess that I need to pick up some books on Electrical Engineering to complete my understanding. I'll try and find these Feynman lectures, Thank you very much again for completing the picture of this for me. :)
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, so what you see on his graph is incorrect, and Derek's answer of 1/c for immediate steady ON is also not entirely right, it's misleading. For the immediate transient, the better model is a dipole antenna model. Also, Derek conflates DC steady state with transient analysis which is false and folks who want to learn, get misled. See my explanation in the main thread.
You're making a lot more sense than the original video. The Veritasium video seemed to imply to me that the existence of the wire would be irrelevant over that distance. Of course, it's evident for short distances that the wires don't have to be connected to transfer power, with for example transformers. But the details concerning thickness, resistance, distance, power , ac/dc, etc. matter a lot, otherwise every device and circuit would interfere with each other and be practically useless.
It seems to me like Derek tries to make concepts appear to be as counterintuitive as possible instead of trying to explain the concept as clearly as possible. I might be wrong that he's doing this on purpose to generate more commentary/discussion/views, but the end result seems to confuse more people than it does explain the concept clearly.
I would argue that the original video is wrong. The reason being that the magnetic filed is made by moving electrons. The field is just breaking the electrons from moving att full speed.
@@Kanglar , I think so. He throws the baby out with the bathwater, so to speak, by making a technically correct explanation seem as though it has no value. There are different levels of abstraction that can be made for various phenomenon and those all can be correct. I found his video good, but slightly misleading because of that.
hmm is the wire sort of is irrelevant because you don't require a wire to transmit power.. There are a number of mediums that can transfer power...?...
The surface charges are already along the wire. When the switch is thrown a current is created, making a B field, now power can flow through space. As real wires have resistance, power also flows into the wire where it is dissipated. It is not bad to say that the only purpose of the wire is to allow a current and the role of current is to make B.
40:24 What's missing in Feynman's Fig. 27-5 for the steady state is the electric field component perpendicular to the wire due to the charge distribution in the conductor, which together with the magnetic field makes a Poynting vector (and therefore energy flow) parallel to the wire. Feynman's figure only shows the electric field component due to resistance, which causes some of the energy flow along the wire getting directed into the wire. This also means that most of the energy flows outside along the wire, not directly through space from the source to the load. I would argue that answer "B) 1 s" is therefore closest to being correct since only a small amount of energy due to transient effects arrives at about 1m/c.
With regards to fig 27-5, are you saying there is non-uniform charge radially in the conductor at steady state DC? Is this not what Dave was talking about re skin effect? Or is this another caveat?
@@Aor87 I am talking about surface charges in a DC circuit. This is a different concept than the skin effect, the latter of which only occurs for AC currents. Surface charges seem to be an often ignored detail when people talk about DC. Think of Veritasium's circuit with zero-resistance wires. In steady state, the net electric field inside the conductor is then zero, but there is an electric field on the outside of the wire coming from the surface charges. This field contains the energy, which is transported along the wire. So while it's true that the energy does not flow inside the wire, it still flows mostly close to the wire where the electric and magnetic fields are the strongest with a Poynting vector approximately parallel to the wire.
As member of general public: when I finished viewing veritasium video, the first thing I thought was... "Ok, then if I put the bulb into a Faraday cage, the cage would block the electromagnetic field that comes through the air and the bulb wouldn't light on". And thats absurd. Therefore, it would be quite more complex. If I haven't misundertood you, your explanation saves this problem. Thank you.
Actually at exactly 40:24 they measured exactly 6.9 level Earth quake on the magnitude scale at Altadena, California. The first responders at the scene found that the source was Richard Feynman's grave, where he had been turning violently. The cause was later determined to originate from an EE misquoting him.
@@dbenitopperez Faraday Cages only work if there are no holes (especially no holes with wires going through!) Yes, if we connect a no-holes faraday cage ( REAL faraday cage) around the bulb, it will short out the bulb, there will be no EM fields inside the cage, and the entire current will be across the outside of the faraday cage.
The "low frequency" "circuit type" engineers do not necessarily know the transmission line details. I can remember talking to a digital design engineer that I worked with at IBM, who had graduated from Cornell, and I was trying to tell him about how a step function can bounce off the end of an open circuited transmission line and the voltage will double... so a 10 V step can produce a 20 V voltage for a time... and he would not believe me.
He just probably never had any experience with RS485 lines, never connected an oscilloscope to the lines at different places and newer given the question of spacially distributed elements of the circuits enough thought. Just give him some time, reality tends to enlighten us once we lose any way around properly facing such a problem in a design and have to understand what is going on. Many other small discoveries are awaiting him along the way as well! Like having a voltage between different "grounds" or magic changes of voltage levels, magic 110ohm load from even an open twisted pair and many others. I am even a bit jealous. I wish I could experience that one more time.
@@Kirillissimus he just thought that Kirchhoff's Voltage Law always applied. He thought that you cannot have a 10 V voltage source creating a 20 V voltage without a negative 10 V voltage somewhere in the loop. He said "you don't know what you're talking about, you are obviously wrong." There was a bit of "I went to a better school than you and you're out of your league and claiming ridiculous nonsense since you don't know better, and I do."
I think the visualization is a bit misleading, giving the impression energy basically moves directly between origin and destination as long as there is a physical connection "somewhere". They have the yellow energy lines looking like they are completely independent of the physical path of the conductors (esp. the ones going straight from battery to lamp perpendicular to the wires). If there was something [impervious to em fields] blocking the straight path between the battery and lamp the yellow lines would not be as "neat" and would more conform to the shape of the wires - which also changes the permeability of space part of the formula he only mentioned quickly at the beginning.
The visual model was impressive but quite messy. i actually mentioned that in another take I did that I couldn't use before I goofed the system audio setting.
The wires control the current and the current makes B. In this way the wires influence the power flow. The Veritasium video shows power along the wires, something left out by almost every text book ( well physics text book, I don’t expect engineering texts to do any better).
I get the feeling his video might leave the general public with a poor understanding. As an engineer, I hadn't thought about how large a portion the surrounding magnetic fields was compared to the amount of power in the wire. But I also work mainly on batteries and motors, so nothing over long distances. I would have thought no more than 10% of the power flows outside the wire, but maybe it's more.
Pretty much. People gloss over the spherical cow in a vacuum type assumptions required to arrive at the conclusion, then try to to apply to reality. The more closely an equation is to mimic reality, the uglier it'll get.
Didn't you say that Grant Thompson from the king of random dying in a accident was his own fault and then change your channel name to hide from the backlash?
Yeah, as a non-electrical engineer Veritasium's video made me think I had missed something, but it's just the small amount of capacitance between the lines that lights the bulb. Seems there was a lot of missing information from the video that will leave people without a full understanding.
I think you're right, and it's not hard to figure out who will be most affected by the misunderstanding. We have an environment right now where people are going crazy for no reason over 5G -- literally tinfoil hat kind of stuff. If they start thinking that all of their power plant energy delivery is coursing through the space between their ears instead of hugging the wires, who knows where it could lead :-).
Take a look at his entire channel and try to figure out who is audience is. His audience is primarily the slightly-better-than-averege layperson for the topic of the specific video. His example of what he used to teach students looks very much like a High School explanation, not a University Engineering explanation. His explanation in this video is explaining nuances that I didn't learn with my 2 year degree in EE Technology, so I would say that his audience for this video is anyone who is interested in electricity who have a 2-year degree and less, not someone who has a 4-year EE degree...
Great Video. As someone who always kept asking "why?" and "how exactly does this work?" during physics classes un school, i am a bit disappointed that people aren't taught this. I know it's easier to look at it as if the energy is flowing through the wires, but nobody ever teaches the "true" version. Amazing to finally understand this. Now will it help me in any way? Probably not, but i love understanding the universe more and more.
If energy doesn't travel "in the wire" - then why does the wire increase in temperature when a current flows ? - Try connecting say a 9kW shower with thin wire... and see what happens!! Or - does it suggest that there is a "resistive" part that heats the wire... and the transmission in energy outside the wire can be thought of as a "reactive part" - ie dissipates no power..?
@@eric4709 Right. Of course the majority of the energy will actually travel IN the wire and not outside it. What most people seem to forget is that the em field also follows the inverse square law. So the further you go away from the field source (i.e. the moving electron), the weaker the field gets. So the majority of the actual power transmitted is inside the wire. Otherwise when you close your hand around an insulated wire and all the energy is transmitted outside the wire, 99% of the energy would go through your hand. However since there is no conductivity where actual electrons can enter / leave your hand, you do not get shocked. Technically EVERY macroscopic physical interaction is the em field or gravity. There are only 4 fundemental forces in nature and most of them are the em field. So while the weak gravity from earth pulls you towards the center of earth, it's the em field of your molecules that repell from the molecules of the ground. "Atoms" do not actually collide when you hit a solid surface with your fist. It's the em field of the atoms which repell each other. All of chemistry is only about the em field and the interactions between atoms and molecules. So technically the example with the metal chain, it's also the em field that is moving the chain and transmit the energy through the chain. How do you think do the chain segments "collide" with each other? Right, the em field of the molecules. So I don't get why everyone is so hyped about "yeah it's just the em field and not the electrons". That's just not true. Without the electrons you don't even have an em field. Also think abour the spatial power distribution in the field. Everybody knows magnets. Same inverse square law. If you get further away, the effect quickly becomes unnoticable. So this whole "any amount of power" (which was later added by veritasium) is complete nonsense and distorts the actual thing you want to explain. If the question was "when would you notice that the switch had been turned on at the light bulb?" everything would be fine. The amount of power that is actually induced on the other side is very small. So we're not talking about transfer or power but just signals / information. So just to be clear: Probably 99% of the power is transferred INSIDE the wire through the em field. The drift velocity of electrons changes proportional to the strength of the field which is also directly proportional to the current. In the veritasium video it sounded like the electrons move very slowly at a constant rate which is not true. It's directly related to the current. Yes, in AC we have no net movement but that doesn't change those facts. If it would only matter what happens outside the wire, why would it matter what diameter the conductor has or what material it's made of? I don't get why so many directly agree 100% or 80% with Derek. The way it's presented is just misleading. When I pay a house and I say "I'll pay it tomorrow" and I plan to pay only $0.2 every day, can I claim that I have paid for the house? Technically yes, but practically no.
17:13 if an ethernet cable is submerged in water, or if its casement is flooded, you will have noticeable attenuation in the transmission. its specific enough that Fluke has a cable tester that can detect if a cable is submerged, and how far down the line the fault is. as far as i know, Fluke engineers have the patent on that. i happened to meet one of the Fluke engineers working on this problem, and he did his testing with a big plastic tub of water next to his desk, and a coil of ethernet cable in the water lol
As a member of the general public: when I finished watching Veritasium's video I have gotten the impression that faster than light communication is possible, because i missed that the exact arrangement of the wires is important. Thanks for clearing this up for me, I might be interested in learning more about this as a result =]
the important question for me is what happens if someone cuts the cable at one of the far ends (150,000 km away), how long would it take for the bulb to turn off? it certainly has to be 1/2 second, because otherwise the information that the circuit is no longer closed would be travelling faster than light. But if the cable was cut before closing the switch, you could close it and see if the bulb turns on after 1 m / c seconds. If it doesn't then the information that the cable is cut traveled faster than light. So how can the circuit "know" that it's complete in just 1 m / c seconds
@@_invencible_ Electromagnetic induction? The wires close to the battery and those close to the lightbuld are just one meter apart, the lightbulb and the battery are just one meter apart. The switch is close-by too. Flick the switch, cause the electromagnetic fields to change, cause electromagnetic induction between those close by wires, power the light bulb for a bit. But, without making any calculations, which I'm not even sure I could make, I doubt the energy transferred would be enough to actually light up the bulb, especially at 1m/c time.
=RNGFN= _Invencible_ Well the electrical engineering answer would be that it does not matter if you cut the wire before closing the switch because the energy capacitively couples from one part to the other, just as shown in dave's video in his simulation. The lamp would turn on and eventually turn off once the transient is over. The time it can stay lit would depend on the actual capacitance between the two wires and the impedance of that light bulb and some other stuff like inductance in the wire. (well, keep in mind that with real components it might never actually light up..) Hope this helps and isn't too complicated for somebody with no EE background.
=RNGFN= _Invencible_ Okay, I think I got what you are thinking about. The capacitance I am talking about comes from the fact that there are two wires laying 1m apart for 150.000km long ends. I am not talking about the capacitance at the point where you cut the wire. While that capacitance exists, it would be so small compared to the wire-laying-1m-apart capacitance that it is irrelevant.
Veritasium is very much geared towards the layman and gives good insights to the more interesting aspects of science while leaving out the details. I think he steeped over the line when he mentioned that there are lies taught to us in school. There aren't any lies, just simplified versions of science that match the current understanding of the student. So unless you study engineering or physics at the college or university level, then all you have is the simplified version. I like the conversations that have been brought up from Veritasium's videos recently.
Veritasium is doing more lying than any school teaching this subject. The schools are teaching this more accurately than Veritasium is doing. Sadly, Veritasium is outside his area of expertise about this topic.
I one heard Neil deGrasse Tyson describing it as "teaching on a 'need to know' basis", as going into full detail would just overwhelm any student and would take way too long to get to the actual point at hand. So you start with the most simplified high level view, leaving out a lot of stuff first, and then start adding things back bit by bit. That "leaving out the details on a 'need to know' basis" can be considered lying in a way, technically. But it lacks the intent to deceive that would be needed to make it a real lie.
@@hartmutholzgraefe I also like the explanation of the need for these kind of primer "wrong concepts" in the Science of Discworld: “A lie-to-children is a statement that is false, but which nevertheless leads the child’s mind towards a more accurate explanation, one that the child will only be able to appreciate if it has been primed with the lie”. An example: teaching the nucleus of an atom with electrons going around it like a mini-solar system in clean orbits in order to later teach the electronic cloud model.
If you watch some of his recent videos about RUclips and clickbait, he probably does this on purpose - he knows how to play the RUclips game and something about "the lies taught to you in school" or "the truth about electricity" etc. is going to get more clicks than a bland sciencey-sounding title about EM fields.
And Veritasium is a physicist and not an engineer, it is just a difference on point of view. The information is correct considering the simplifications.
And therefore the 1st explanation is the best one for us idiots or this idiot anyways this extra stuff you're adding is more confusing than the 1st 1. Otherwise you need to be in a form that's for the professionals not the idiots like us or me anyways.
I am delighted whenever I hear engineers who are rigorous and show a proper understanding of the fundamentals down to a sufficiently low level for the topic at hand. Unfortunately, in my anecdotal experience (that is in no way a proper statistic) very few engineers care or are knowledgeable of the underlying science behind the practical equations and models. Also in my anecdotal experience, it's only the engineers who do care that make progress in their fields, either as researchers, designers, developers, or troubleshooting and optimization. For these reasons, I subscribe to engineering channels like this one and enjoy their content so much. Great work, Dave; thank you for the content!
As a computer engineer, we focused more on the practical side than the theory side when we covered electricity and circuit building, and this was news to me. (It's possible we glossed over this in class and I don't remember but we definitely never went in this much depth). This was rather counter intuitive to me and my mind is blown. I love that I can be this wrong, the more I learn the less I know. Thank you for the knowledge and praise Maxwell!
Same for me. I don't understand Dave's exasperated "WHO THINKS THAT?" followed by "All engineers know that". He keeps on answering his own question: the rest of the world. Veritasium is not aimed exclusively towards engineers. Actually, I'd say its rather the opposite. Derek never claim that this is unknown. Just that it's a common misconception, which I can bet everybody's asses that it is.
If you had taken power systems engineering (I had one semester) electromagnetics, or RF design (which requires the previous as prerequisite), Poynting vectors and fields in general are thoroughly dealt with in those courses. Computer engineering blows past a lot of fundamental engineering. I was an embedded systems and instruments guy myself, the computer engineer in me was developed because of market conditions, not coursework. Although I had 1 graduate course in computer architecture and 3 courses in C/C++ years later in community college.
This is the vibe that I got from the Veritasium video too; not wrong, but a bit sensationalist, not sneaky, but avoiding certain key elements in order to get wants out of the audience, and the physics perspective all the way.
the target audience isn't engineers, he can't list all the factors otherwise it'd just become engineering/physics courses. we can add temperature and so on...
@@alexisfrjp Anybody who isn't angry about the details of this video clearly isn't an electrical engineer and even as an engineer from a different field I find it a nice mental model for my dumb ass brain.
Yeah, veritasium is mainly doing things sensationalist these days because he's mainly after view count. He genuinely wants to spread good information, but he realized (and said in another video of his) that he HAS to make it sensationalist because that's the only way to survive on youtube and make money.
24:10 as an electrical engineer myself, *THIS* is the main issue I have with this video. It tells people that _"all energy is delivered outside the wire"_ - which will make them wonder if their electritian is trying to sell them unneccesarily thick/expensive wires, as the energy does not go "through" them. A followup video diving into this would be super interesting I think. :)
The Veritasium video is spectacular. Revealing to the general populous how electricity actually transfers energy is not going to make people magically stupider. Wire sizing is a thing, and I'd suspect more people are aware of wire gauges and amperage than they are of Poynting planes. By explaining to them how the fields carry energy simultaneously while the electrons inside the wire flow, I don't see where anyone would get so confused that they begin second guessing the electrician they hired regarding anything he suggests.
Thanks Dave for your unagitated and professional and way reacting to this. I see the point made on the veritassium video, however for the general public and the average guy, it's like considering Einsteins relativity theory every time using a GPS. Side note: My flux capacitor equations never gave back 42, maybe because I neglected this fact we have learned now. Jeez...have to do it all over again.
GPS only works because of both general and special relativity. The fact that we don’t need to understand these subjects to use GPS does not mean some of us need to, and for the rest it is cool to know the deeper truth.
@@jimmcclymer4230 Do you actually have a credible source for that Einsteins relativity was needed to develop GPS. I have read somewhere that the corrections for relativistic effects are done with calibration parameters on the clocks that are determined empirically through measurements rather than through theoretical calculations. I know that it is often stated that relativity theory was needed in the development of GPS but to me it makes sense that you would just measure any drift in the clocks after launch and compensate for it. From a practical point of view it does not matter if the drift is due to relativity or if the clocks just got out of calibration during launch.
@@Kandralla Yeah it annoyed me - he's structured the video like a 3 card monte to generate controversy, comments and clicks rather than trying to explain the subject in an understandable way... And he does know how to make good educational videos when he wants to.
My biggest beef was the as considering the tiny voltage that you get through the air as "lighting it up" it basically destroys the concept of circuits to me. Any source that you hold technically lights every single lamp in the world because the electromagnetic field has infinite reach.
Almost every one who isn’t in the “field” thinks this way. Like high way’s cars go in one direction and then back. It may not be correct but I bet the most outside the “field” visualize it that way. BTW why has his video clip gotten so much reactions? (The question is more in general, not to this specific post). :)
“Derek is correct” But the reactions point to “bloody murder!!”. Not specifically a comment on this specific video or channel (actually this clip was pretty balanced and good by me). But where is all the reactions coming from? Seems like people haven’t had a shit in two weeks and finally find a toilet.. ;)
Yep! 99% of the public probably think that (myself included) - which is who Dereks videos are intended for. He's not trying to teach an electrical engineer something they most likely should already know.
I am an industrial electrician specializing in industrial automation. The examples he gives and the lump theory that he explains he thought is what electricians are tought in trade school. It's borderline amazing to me, as an electrician I feel like what I was taught in trade school is an incredibly simplified version of electrical theory to help get the masses out I'm the field pulling wire. I have increased my knowledge considerably since trade school but most electrician don't. Infact most electricians don't know what would be considered fundamental knowledge by most electrician engineers.
My biggest issue with Veritasium's video is that he makes it sound like the electron movement is essentially an inconsequential side effect of the energy flow outside of the wire. The battery isn't a magical device that contains vectors waiting to escape. The energy from his lead acid battery depends on the movement of electrons. Without it, the negative plate quickly builds up excess electrons which repels the negatively charged HSO4 ions and stops the reaction. The movement of those electrons is absolutely required.
@@KLRJUNE What carries charges in a wire? Electrons. The repulsive force between electrons will cause an increase of electrons per unit of volume on one end to propagate down and show up as an increase of electrons per unit of volume (and therefore increased charge) on the other end. This is why we don't have to think about drift velocity of electrons in electronics but can just think of the movement of electrons. It's analogous to the air ejected from your mouth when you speak - it doesn't move very fast, but the local change in pressure propagates outwards at the speed of sound. Veritasium's argument comes across to me as "people think that they're hearing the molecules of air you exhale but really it's not air you exhale but the sound waves traveling through the air!" It's a pedantic point, and you can model sound just fine using the movement of air without keeping in mind that zero of the air molecules from the audio source may arrive at the detector.
@@KLRJUNE what you said sounds like you don’t need electrons what he said is that you need but they are not what Carrie’s charge huge difference hence no one got your point at first
@@KLRJUNE you said that the waves matter not the movement of electrons, all iam saying is that the majority of people including myself reading it think you mean electron do not matter only the waves. the dude above you explained it clearer, even if you meant the same thing we didn't get it. so iam glad he explained it in a longer way.
Derek did not give all the details of the wire used (other than "no resistance"), but for what it is worth -- one can model a parallel transmission line to develop the characteristics that may be usable in a circuit simulator. For example, if we assume the wire is 10 gauge and is separated by 1 meter (center to center), the characteristic impedance (Zo) of this transmission line is about 798 Ohms. The capacitance is about 0.04 pf/cm and the inductance is about 26.6 nH/cm (all assuming a dielectric constance of 1.0 -- free space). When the switch is closed, the current that flows will be based on this surge impedance (x2) -- ignoring any lamp impedance -- until the sytems reaches steady state DC conditions. It is not going to be much current during this transient period: 12 Volts / (2 x 798 Ohms) = 7.5 mA ..... Doubt this is enought to light the bulb "instantaneously".
Boom, this is EXACTLY what I was looking for - thank you! The author of the original video conflates steady-state analysis of power with the dynamic step-response of the signal. Before the steady-state is achieved, the initial power delivery is only 90 mW. That would be
@@DeadCatX2 I think the power in the bulb would be even more minute because the cold resistance of the filament is about 10 times less than its resistance when lit. So the Veritasium video is wrong. The bulb will not light until the wave travels to the ends, sees the short circuit and reflects back to the bulb. He should have used an LED as that would light with 12V through 1.6K.
Yep, at this time a lot of people figured it out, that there will be current on bulb, but only small. Lets imagine, you have to have a substantial part of current of your sorce on a bulb to light, lets say, 10% of a source, and your light bulb would not light up on a AC coupling only in this case. And video makers keep ignoring this point of view, concentrating attention that we will have potential difference on a bulb.
This is a great analysis. I had imagined the two wires coming from the battery as an electric dipole and the two wires from the light bulb as another dipole, so it is (for short times) two coupled electric dipoles. Your analysis is a great back ofthe envelope calculation.
So at 0.04 pf/cm it is the equivalent of having two 12,000 uF caps in series with the light (ignoring resistance and before the current gets all the way around and it reaches steady state)
As an "IoT engineering" student I can say that you are wrong in saying "every engineer knows that". My course never mentioned that and It felt so weird to watch this video about something I thought I knew well.
Plenty of graduate students carry around this mental image, 100 %. You still can abstract it away because you just learn the idioms of... whatever you're doing, but getting rid of how you visualize already super out-there things (if you think of electrons, do you assign a color to them mentally and what do they even look like? Does anyone not have a picture of black holes popping when we're talking about electron holes? What about doping?) is really, really difficult - and possibly not even that interesting. You just map your general understanding of a small problem to a unique visual (or sensory) landscape and that's how, say, "electricity" looks to you. It's almost a matter of language, as is so often the case - someone mentioned Mehdi's Kirchhoff battle I vaguely remember and as so often, it boils down to how you phrase a question, definitely something Derek touched on too and many other RUclipsrs. Most professional engineers and scientists are severely limited in terms of conceptualizing different aspects in novel ways, and we all can sympathize with the notion of just having learned one tool properly - why would I invest 5 more years learning another DAW when the one I used for the better part of my life is almost part of my brain at this point?
Can confirm this. As an Embedded Systems Engineer, in college our focus was mainly on digital systems and software. Our electronics class pretty much peaked at calculating capacitor and inductor phase shifts using complex numbers. Saying "every engineer knows this" is a bit unnecessary, because not every engineer is concerned about this aspect of electronics, or electronics at all.
I quite literally design transmission lines, and the whole time I was watching Vertiasiums video I was thinking to myself "yes but....." Generally, it's not really a useful way to frame things and it's clearly just for the 'wow' factor that it gives a general audience.
As a physicist, I agree with you that this is not at all useful for day to day work, but it is cool. Typical of what we do in physics to simply the problem until it is beautiful - Oh and we got to the beers long before the engineers! (Although if I had to solve it I would treat it as a transmission line!)
@@morethan4mph finally a physicist, thank God Why doea it happen faster than the speed of light? I mean, wth, the information that the switch is closed shouldn't be capped at the speed of light to travel across the wire (or around)? Like, current, EM field, gravitational field waves, ain't *everything* capped at c?
@@morethan4mph oh, thank you for responding! :) But wait, if it happens at the speed of light, and the wire is one light-second long (or the half of it we'ee calculating on) shouldn't it take at least one second? 🤔💭 (Supposing everything is ideal, super disclosable, don't oscilate a bit to establish, etc)
It's all about models. If you want to derive the ideal gas equation, your atoms or molecules are tiny billiard balls. If you want to explain the Rutherford experiment your atoms have a positive nucleus and negative electrons. If you want to explain the Chadwick experiment then the nucleus has neutral particles as well as positive ones. And so on. In electrical theory, electric current flowing in wires like water in pipes is a perfectly adequate model for explaining what's going on. You choose your model to fit your purpose.
Also, Dave, thank you for mentioning the Feynman lectures on physics, that being available for free online made my day! I foresee many hours spent by me reading that stuff.
The youtuber "AlphaPhoenix" decided to actually do a physical test of the thought experiment in their video "I bought 1000 meters of wire to settle a physics debate". AlphaPhoenix also did a follow up video expanding on further questions "Why does WATER change the speed of electricity?"
What a fascinating 45 minute rant. As an engineer, I love it because I can so much relate to it. (However as a mechanical engineer, I deal with different misconceptions)
I'm glad you cut the wires off at the ends in your little example. They were always just bait to make things messy and confusing and him putting them there just rubbed me the wrong way. Your explanation with no bullshit (although you didn't really say anything particularly new to me either) was very nice and clean.
I guess everyone needs to define what 'on' means. For Derrick's answer, 'on' is any minute power dissipation in the lamp (and his answer is correct for that definition), but my first reaction is that 'on' is the full power dissipation allowed by the impedance of the lamp, and the power source. This version of 'on' is not reached until the EM propagation is allowed to travel through one half of the circuit. Before t=0, another assumption can be made that circuit is in state with the switch closed, meaning that the entire circuit is at the same charge between the left side of the switch, and the same charge on the right side of the switch. That EM charge is unfolded at the speed of light after t=0 and the light goes to full 'on' once there is a positive charge on both sides of the lamp (ie c times half the circuit length).
This is what confused me at first too, especially after he had all these EE guys talking his claims up. The lightbulb is probably already "on" just from random background charges moving: no power source needed! His explanation is not really what most people think of when they think of "on".
Exactly! The whole topic is ill-defined. It is basically impossible to do any useful lighting (even if ignoring all the effort to make the element inside the bulb to start to glow) before 1 second.
This is the first explanation that makes any sense. In a pedantic and nitpicky sense, the moment the switch is closed, changing electric and magnetic fields propagate from the battery terminals and its adjacent wires, to the bulb and its adjacent wires; but this power transfer is incredibly weak, and may not even cause a single photon of light to be emitted. Derek assumes that one photon DOES get released immediately after the switch is closed, calls this the "ON" state, and drops his mic. There's got to be a better way of teaching Poynting Vectors and EM power flow to kids, without causing this level of confusion, which is based on an impractical technicality. Maybe replace the DC battery with high frequency AC source, and have the target bulb be something that can be usefully energized by that source. I'm thinking of something along the lines of the "fluorescent bulb lights up by itself near high voltage AC lines" demos have been around since forever.
Thank you for this video. I am not an engineer, but an electronics and ham radio hobbyist for about 45 years (and biologist). I like how you explain the different perspectives of engineer and physicist, and allow for the differences due to intended audiences. Usually it is not required that analogies be totally faithful and descriptive of reality, if they provide some increased understanding! I will keep studying the physics, and the transmission line theory, but I will also keep building stuff like 9:1 unun to allow me to use non-resonant wires for my antenna systems. I am often having fun with other people's designs. In our radio groups are some retired electrical engineers and I am always so amazed at how they build stuff based on their OWN designs. Wow! Keep having fun learning, and (if you are so inclined) building stuff! Both can be VERY fun. Dave WA4NID
I have to point out the comment where it was said that “everyone knows this,” when referring to EEs. I can’t speak to physicists, but I can tell you that if I asked my colleagues at work what drift velocity was, even just at a high level, they would scratch their heads in confusion. Some might say “oh, I believe we learned that in General Physics in undergrad.”
Well it depends on the field of study and working environment obviously. I'm studying mechatronic engineering and we do see quite in the details the physics behind semiconductors in various courses about design of electrical control for motors for example, but we've done drift velocity during the introduction to "electronic & electrical motors"
This. 99% of the population probably has never heard of any of this and at best thinks magic electricity (maybe electrons) is being pumped through hoses (wires) in to the end device. Among engineers: would bet an EE knows this, but probably not an ME (short of some elective class they barely remember). Physicist: same thing, depends on the type. Virtually any other major is probably shocked to hear the answer.
i agree. i asked some engineers and physicist. the physicist knew the drift velocity speed roughly but didn't really understand the answer to Derek's question. the electrical engineers didn't know the drift speed and when presented with the answer to dericks question was "Sure if you say so" i certainly was not taught propagation speed or drift speed in my formal education. I worked out the propagation was roughly speed of light when i started working with transient situations and always assumed electrons moved very quickly but less than speed of light. that was interesting to find out but frankly arbitrary
You said all I'd have liked to say. Well explained! He implies the bulb turns on, as in "it turns on normally (100% power), and remains on" and that is clearly not the case! But yeah... the physics are ok.
The physics is totally wrong as he assume the bubble start emitting light instantly as the electric energy is fed to it. Sory it's wrong, that bubble first need the switch mode converter to stabilize then the decoupling cap to charge up before the LED start glowing ! And if you want to get picky about what happens in terms of reflexion in the line, although that will only account for a super tiny irrelevant fraction of the turning on time, then you must acknowledge that the damn PSU in those modern bulb is by no mean a "nice" resistive load as used in the calculation we made at EE university (That's why for more powerfull unit you need a prefiltering stage before the actual AC/DC converter so you don't mess up too much with the cos(phi) of the power line). Fact is understanding things at this level would be a mathematical nightmare and once again it doesn't matter as in the real world that switch to light time depends probably as much on that than on the noise. So yes "assuming a perfect world that doesn't exist where everything would go according to the equation i want to demonstrate then the physic is right". To me that's an oxymore to say it's wrong.
Magic light bulb, the transient will be over long before the filament heats. I thought for a incandescent bulb on time is defined as 90% filament heat. If using a LED will it even get to forward voltage?
18:45 is honestly the most important part between actually useful content and garbage. 19:42 is actually the part I find worse... Since it is a video targeting popular science. It is generally missinformative even if it is technically correct if one accounts for the intentionally left out information. (36:50 I like to remind you Dave that the video is for the Regular Joe, not engineers nor physicists.) 35:30 yes if the circuit were a circle, then it is the diameter of the circle divided by C seconds, But the thing that annoys me with videos like this is that they don't actually explain things properly. Leaving the viewer with 1 answer that is only applicable for the ONE example scenario. While not providing the viewer the answer to Why that answer is correct in that scenario. So I will dread having to deal with people who from now on thinks it takes 1/Cs for any electrical connection to be established. Though, depending on the material between the wires, it can take a lot lot longer than 1m/Cs unless we do the setup in perfect vacuum. The speed of an EM wave in a material after all isn't C (it is dependent on the relative permittivity, also known as the dielectric constant), but that weren't even mentioned, despite being a major spec of most transmission lines. (Though, doesn't stop even experienced network technicians from believing that their fiber optic cables goes at 300 000 km/s, even if they typically only go at 60-75% of that. The dielectric constant of glass is fairly high.)
wtf there was no info left out. He literally shows the bulb & the battery 1 m apart "While not providing the viewer the answer to Why that answer is correct in that scenario." he literally spent the whole video explaining why it is 1/c s btw 1m/Cs is bad form for 4 reasons 1) 1m = mixing variables with units = confusion. If you want to write 1 metre it is 1 m 2) Never put units on the left hand side. It is a waste of time & it's mixing variable with units 3) it is not big C it is small c 4) cs is wrong. The correct form is number space unit e.g. 5 s not 5s & c s not cs & 1/c s not 1/cs
I'm sure others have pointed this out but a quick point about the 1/c thing, if you do unit (dimensional) analysis on 1 m / c = 1 m / 3*10^8 m/s, so unit analysis the fraction we get is m / (m /s) = s. So it is 1/3*10^8 second not 1 m / c second or whatever. Ideally if we had a standard math function like absolute value but that was unitless value that turned a quantity in some units into a unitless coefficient you could use that. I'm not aware of such a function but taking a cue from absolute value function if |x| is the absolute value of x, let >x< be the unitless value of x. So >c< = 3*10^8 [where c is specified in meters per second]. So using that the answer d) should have been given as either: 1/>c< s or >(1 m /c)< s or if your willing to let the reader do one's own unit analysis etc. 1 m / c [in meters per second] or if you want to have a bunch of ugly number hanging about 1/3*10^8 s Obviously unit analysis gets more of an emphasis in chemistry or solid state physics (personally I only passed stat mech by looking at a problem looking at the equations I had access to and figuring out how to Rube Goldberg myself from the set of units specified in the problem to that required in the solution), but it can trips us up almost anywhere.
There was a lot of missleading things in Derek's video, and it took me days to finally figure it out. I never had the same definition of "turning on" as he did. Sure the initial change is at 1m/c s due to capacitive coupling between the wires, but the lamp won't see significant power until it reaches steady state, 1s later. As Dave said, make the circuit a circle, or just seperate the two wires further apart and it changes everything. Derek's video should have been more about capactive coupling between two wires instead of focusing on EM fields. The topic had nothing to do with the quesion/answer. Very missleading. "switching on" instead of "turn on" would have already made it a little clearer. Very missleading, since the lightbul won't be glowing at 1m/c s.
Even in a classical sense the light bulb would light up in 1m/c seconds because as Power = Voltage x Current. The voltage would as explained in this video propagate at the speed of light and the current starts immediately after the switch is closed so yeah it’s still 1m/c.
@@parryhotter3456 'the light bulb would light up in 1m/c seconds ' You guys realize the lightbulb would really never light up due to power sources not being able to drive 300,000KM of line and deliver power to the bulb, etc.. By focusing on one variable and pretending the others are infinite and infinitely efficient, etc, the whole idea is like any other fake 1=0 proof. You're roughly accomplishing a multiply by infinity or divide by zero by calculating on the 300,000 KM lines when the reality is none of that stuff would be driven that way when you start taking the other variables into account.. IOW a 'Reductio ad absurdum' type failure, or really probably the opposite of that. Reduced to the point it still seems to hold up, but actually the failure has been hidden in the reduction of variables.. Start calculating all of this out with real 1 m loop numbers and real 300,000km loop numbers and it'll become a lot more obvious that reality isn't going to work this way..
You are exactly correct, the question is meaningless because of the assumptions that are made. The first being you can have a 0 ohm wire. The second being that we define the bulb as being ON when ANY electrons pass through the "bulb". Does some current flow through the bulb in 3.3ns, sure! Is it enough current to be significant, hell no! My hunch is that you would actually get way more current just moving the wire 1 cm/s through the earths magnetic field. And Derek's video either fails to point out, or he didn't realize that the bulb would turn off again almost instantly as the transmission line locally meets steady state, and would only turn on again once the electrical field has populated through the wire.
@@Kindo1085 If you had cared to read through the slides provided by Derek under his video, or if you had considered carefully Dave's lumped element model that places a capacitor every certain distance along the wire until half a light-second away, you would realize that the light bulb will not turn off almost instantaneously. The thought experiment is very meaningful to me. The assumptions help keep the video short and keep me focused: I was inspired by the fact that Maxwell's equation, the transmission line theory, and the Poynting theorem could all lead to the same answer!
Very interesting video even for a non engineer like me (I have a chemistry background). I also think your point of the different mindset is true in every field. I routinely work with electronic density (computational chemist), while I have experimentalist collegues who don't give a crap about the nature of the electrons and deal with reactants and products. We all work within some approximation, otherwise it would take forever to do anything meaningful. It's important to know what's behind the approximation and realize when the approximation break down, but we can ignore it most of the time.
I've watched a few of Veritasium's videos and on the ones I know something about he always seems to leave out important information as well as being for people who don't know anything about what he is talking. If you know anything about the subject you probably already know most, if not all, of what he is talking about. And the answers he comes to aren't necessarily the best answers since they are ignoring vital bits.
If you go back and watch his other videos. You will find some videos that deliberately ask questions and then don't answer them. Guess where the answers are? Next video. More views!! baby!! I hated that kind video so much that I stopped watching a long time ago. But lately he's been fishing really hard for viewing count. Even though I clicked not interested, youtube kept pushing it to my feed. So I clicked [don't recommend his channel]
I couldn't bear to watch the original Veritasium video. As an electronic engineer I baulked at the title. Thank you for sparing me. Your analysis was well done and saved me from that tedium.
Veritasium walks a fine line between thought provoking ideas and unbearable smugness. Ok maybe they don’t walk a fine line, they stagger from one to the other like a drunken scientist.
This reminds me to Ferreira's power loss models for conductors (used for estimating power losses in the windings of transformers analytically). There's a chapter in one of his books explaining how energy is transferred inside transformers and the problems to calculate the poynting vector in a real component analytically (as well as why the rest of the book is technically wrong but provides correct results). Definitely one of the most amazing engineering books I've ever read Edit: I hadn’t noticed that the autocorrector had changed poynting to pointing
This actually helped me better understand his video. Especially because the battery was DC and I wasn't exactly sure what was going on. The instant I saw your lumped element model I got it. Thanks Dave!
The counter-intuitive workings of electromagnetic fields was actually what pushed me over to computer science from electronics. I had so many unanswered questions about why we were using the notion of current being a flow of electrons when it seemed flat out wrong after learning about electromagnetic fields. Turns out that it was just an abstraction (albeit a useful one), but I never "got it" back then. Still puzzled that my teachers couldn't explain this in a better. Mind you this was still at high school level (three year service electronics path), but in the end I felt that I was missing so many pieces of the puzzle that I just changed over to computer science instead when starting college. Very informative video, thank you very much.
when did you change majors? I dropped out of Chem before transferring to New Media. I was looking at a geology course' curriculum and like... I want to go back because it looks like they filled in a lot of holes.
Interesting! Your understanding of the word abstraction has probably changed so much due to your CS education, you may not have liked that answer any more as a high schooler
A major difference in the way we electrical engineers deal with the practical aspects of electrical engineering is recognizing that a true STEADY STATE d.c. circuit ( no time-variant current/voltage changes ) there is no reactance, only resistance. There is no electromagnetic radiation from conductors in a true steady-state d.c. circuit.
Derek's video made it clear as mud... 🤔 The transmission line model makes lot more sense to me. Your videos are highly informative and fun to watch. Learned a lot from you. Thanks man!
It was SUPPOSED to be clear as mud. The objective of this video was not to teach anything, but to show how clever Derek is. He left out a lot that could have made it clear, I would say deliberately. He's trying to set up another bet, like the one he made with a physicist about the wind-powered car that could out-run the wind. And he's trying to get more viewers than he would just by explaining how this works. I've lost some respect for him because of his video.
Thanks for the video and the analysis. Here are some comments: 1) You don't need to add 'second' to the answer when you say 1 m / c. C already has units, so the answer should simply say 1 m / c. 2) In your simulation, you simply assume a capacitance and an inductance for the transmission line and the simulation doesn't take into account the finite value of the speed of light. It seems to me that the simplifying assumption of the circuit is that the transient effects in the circuit are fast enough that the finite speed of light won't affect the result so you can simulate your circuit at 'infinite' light speed. 3) I think the initial transient pulse that the light bulb sees can be more easily understood in terms of radiated waves when you initially turn on the circuit. If I attach two short wires to a battery to form a dipole antenna, at the moment both wires connect to the battery, the wires would emit electromagnetic waves due to the square wave pulse. This can be then received by the same kind of setup with two wires forming a dipole antenna and a light bulb replacing the battery. The received signal would create a non zero voltage difference between the terminals of the light bulb. This doesn't prove that in the steady state, the power is transmitted through the air and not through the wires. The transient signal doesn't have anything to do with the steady state flow. 4) Since we are assuming any non zero voltage is enough to turn on a light bulb, when I do this little experiment I basically turn on all the light bulbs everywhere around the world. :)
@@couplingconstant it is in relativity theory; since c is used all the time, units are dumped out the window, and you see a 1/c appear in a temporal coordinate all the time.
@@takix2007 I'm not sure what you mean by that. Yes, factors of c or 1/c appear and they have proper units. Position four-vector is (ct, x,y,z) and all components have units of length, or four-momentum is (E/c, px, py, pz) and all components have units of momentum. In particle physics you often use natural units where you set c to 1 and change the definition of meter and second. Then you completely drop all the c factors from your formulas since you set it to 1. But that's not what we are discussing here.
@@couplingconstant indeed, that was exactly what I was referring to. And indeed it has little to no bearing to the discussion at point. BTW, you surely meant to say that all components of the four-vector have the *dimensions* of lengths (which can be expressed in units of lengths, i.e, meters in SI) ? 😜
This is a deceptively simple problem with lots of rabbit holes to pursue, but Dave clears up this problem nicely. One of the most interesting classes I took in college was transmission lines in my senior year (BSEE curriculum). In that class the professor very clearly showed that electricity is really light, at least in terms of behavior, but I think even at a fundamental level. Even though this wasn't a class in optics, theories of refraction (lenses) , reflection (mirrors) and other topics were compared to transmission line equations and sure enough the parallels are amazing. Even a radar dish on a jumbo jet behind an "opaque" cone appears transparent at radar frequencies. The cone material is specifically chosen so the impedance is matched. If the wrong material were used the radar would be reflected back into the plane. Light is a coaxial circuit from source (eg an LED) to observer or destination (eg our eyes or a camera sensor). Our existence is a complex matrix of coaxial circuits that we take for granted every day.
I've looked at the two "expert" references in Veritasium's video, they are both useless. The first one produces a waveform with no timescale but is actually the short transient pulse as shown in Dave's simulation. It doesn't show when the actual dc power arrives. The second one does the opposite his analysis only shows the arrival of the 12V at the lamp and the reflections that result from an unmatched transmission line. He only shows the voltage at the lamp and so doesn't show the initial delay at all. It's easy to see how Veritasiuim has been misled by these analyses.
As someone that is not an engineer, it is definitely something very new. Before Veritasium video, then your video and other video, I always thought that electricity is about stream of electrons moving, flowing from the power source to devices.
I thought the same about the flow of electrons being the cause of electricity, and I had to take a digital circuits course in college and took an electricity course as an elective. I think one of the things I have trouble with is that the electromagnetic fields can't exist without the flow of electrons, and of course the flow of electrons can't exist without the electromagnetic force. The thing about electricity in the real word is we have accepted equations, for example Watts (power) is equal to the Voltage times Amperage, and Amperage is a function of the number of electrons in the transmission medium. Voltage is equal to the current times the resistance. It seems to me that you can't have electricity as we define it, without a combination of the electrons and the waves. I wonder if this is just arguing semantics, because in the original video Derrick says that electrons don't carry energy, but doesn't anything in motion carry kinetic energy? It almost seems like the argument is more about the fact that the electromagnetic field is the transmission medium for electricity, but we generate the field by moving electrons. I I were dropping a rock from the top of a building, isn't the rock delivering the energy when it hits something, even though it is gravity that is the cause of that energy? In the end though, it seems like movung electrons will always be required to make use of the electromagnetic field.
I thought Derek's video was the equivalent of a bright kid teasing another by poking them over and over while chanting, "I'm not touching you! I'm not touching you! Technically it's only the repulsion between the electrons in the atoms of our skin that's occurring, nothing is actually touching!" Sure, it's correct, but also deliberately misleading. It feels like Derek's video was made to appeal to those who want to have knowledge to be more correct than others, rather than to be able to use it usefully. I was left more confused after watching it, and I don't know how much educational value it would have to someone even less familiar with electricity fundamentals than me. (I assume Dave's talking specifically about electrical engineers when you say "all engineers know this." It definitely wasn't covered in the single circuit fundamentals course we got in mech eng.) Thanks, Dave, for actually explaining the concepts and increasing my understanding!
Precisely. It was just Derek reminding us that he is so much more intelligent than the rest of us mere mortals. I remember some kid played that game with me in grade school, the I'm not touching you game.... I smashed that kids head through a desk. Then I said... "Oops, I win."
As Rush Limbaugh once said "Words mean things" Things are actually touching. They are fields. They touch by exchanging photons. If you,ve ever been hit with a snowball you will understand the analogy. There is no action at a distance. A theory can be based on incorrect assumptions and still make corrections as accurate as the current state of measuring devices. Epicycles was one such theory.
Yeah, it's like asking "is a human made mostly of water, vacuum, or something else?" and then mocking someone for whatever answer they pick. "No, it's mostly water, that's the most abundant molecule in the body!" "No, it's mostly vacuum! By volume, all atoms are over 99% vacuum!" "No, it's mostly baryons! Over 99% of your mass is in baryons!" I mean, he went on about how power lines work, then used an experiment that works entirely differently to get that initial spike, which would still go through even if the lightbulb and battery weren't connected. I don't know why this angers me, but I had to vent. Maybe it's because flat earth proponents use the same sort of equivocation. It's maddening.
I think Derek is trying to inspire people to learn more about stuff he has videos about. It seems to me that none of his videos are supposed to cover the video subject fully but just give a glimpse and raise additional questions.
@@MikkoRantalainen At last, someone who "gets it". Thank you! The derisive comments above are typical of a certain mindset, they can't see beyond the end of their nose. All of Derek's videos are designed to make you think, to challenge what initially seems "obvious" and to inspire people to learn more. The fact that in doing so, he angers a few narrow minded people shouldn't stop the majority of people watching and learning.
Electroboom, I'm a retired electrical engineer. I love your video. I wanted to say, importantly, the word is impedance NOT impotence!!! Yours is the third of three videos I've watched on this. First was Veritasiums, then Dave at EEVblog, then yours. Dave said that we engineers think about things differently. That we have tools to analyze things and validly track physics and the rules of science. You fellows have collectively reminded me of much of the complexity we were trained to understand and analyze and calculate. I've much forgotten what I was trained and educated to deal with. I've been so browbeaten by the mindless politics and public chaos of people and the media news etc. I've forgotten the promises of my youth and education. RUclips, multimedia and Internet is a terrible way to waste a capable mind. You've helped to retrieve my past capabilities. Thank you. Amind is a terrible thing to waste, and you've given me a wake-up call.
A more interesting question might be ”how much time does it take to switch off the light” with a massive transmission line & a resistive load (probably arbitrary & unmatched)? With all that capacitance & an unmatched resistive load, it could take longer to turn off. Same issue as the first undersea cables encountered. It distorts the sharp rising & falling edges of the signal.
And how long does the light in the question glow with the small current if the wires are open at the end? Is it a flash of next to 0 time? Is it a flash 1m/c in duration? Does it stay on until the light speed feelers reach out to the ends of the wires to discover its open? Does it stay on forever because the bulb is infinitely sensitive and the fields will never completely stop?
I had another thought. The circuit should have a time constant if it’s a capacitive & resistive line. The time is t=RC (in its most simple form) but didn’t Derick say the resistance was assumed to be zero?! If that’s the case, by his own constraints, the t should be t=0 x C. Anything multiplied by zero is zero so the answer should be d because the resistance of the wires is zero so t also = zero not 1m/c m/s. Just a diverse thought :) ;).
The thing is, the distance does matter for the interpretation of your simulation. The capacitance of two wires 1m apart is more in the range of 10^-15 F. That leads to a much shorter voltage peak. The energy transferred in a peak that short is not enough to "switch the light bulb on" in any conventional meaning.
theoretically, the voltage peak would be the same height, voltage can't change across any capacitor instantaneously. if dave used more accurate & smaller values for the capacitance, the transient spike would decrease faster, but he specified that he didn't care about that for this simulation
@@stulora3172 The thought experiment is not about generating light in a bulb or LED but about the moment current starts flowing in the resistance of the load no matter how small it is.
@@ZeroInDaHouse Yes. Don't get me wrong, the simulation was very helpful and overall, Dave's approach helped me understand what happens better. No criticism. I just wanted to do the next step by evaluating what this means for the actual thought experiment. And as we are talking about "switching on" the light bulb, I wanted to point out that we would not get any perceivable light from this path of energy transfer.
Whilst we all treat ac and dc circuits differently for practical reasons, everything that applies to ac circuits must apply to steady state circuits otherwise our understanding of physics is shaky. Essentially a steady state circuit is just one with an infinitely long wavelength (relative to the length of the circuit), so all the relevant terms drop to (near) zero and can be ignored. When Derek started talking about undersea cables, I instantly thought "yeah, because it's now a transmission line where the length of the cable is relevant given the frequencies you are sending along it". But his video wasn't aimed at engineers - and like you said, if it sparks an interest in science/engineering, that's great news!
The simplistic visualization that I've come to love is the one of the Newton's Cradle. Imagine electrons in a circuit as being like the beads in a Newton's Cradle. The beads/electrons themselves aren't energy; they're just transferring it between each other eerily efficiently. And through this same visualization you can also begin to imagine how there can be factors that affect that efficiency.
That visualisation is no more correct than the naive "electrons are like water" interpretation though. The electrons themselves never carry energy. The power also doesn't come from them pushing on each other. The electrons are simply worked by the electric field, are induced to propagate changes in the electric field into the magnetic field, and by doing so create a favourable combined electromagnetic field that power can flow through. They never carry energy or power, they are little links in a chainmail of energy transfer.
@@Gyzome I have always been taught that electrons are the cause of the magnetic field. If they didn't exist, then we couldn't use wires to generate the magnetic field that powers electronics if this is true. It is very possible that the courses in electronics just don't provide the physics behind this, though it really seems that electricity needs electrons and magnetic forces to exist. It is hard for me to reconcile the reality that larger diameter wire is capable of carrying more current if electron movement plays no role in carrying electricity. I have always been taught that moving electrons will generate a magnetic waveform, and that a magnetic waveform will always move electrons (mostly this is from antenna theory). The implication to me seems to be the two are tied so closely together that it is effectively the same thing. Maybe the issue I have understanding this is that a pure physics point of view, classifies energy using specific definitions that are outside the requirements of antenna theory. My thoughts on the 1/c answer is that the battery side of the rectangle is acting like an antenna to broadcast an EM wave, and the light bulb side is acting as an antenna to relieve the EM wave. The movement of electrons sync up and move through the bulb to produce the output. In the point of bulb output, the output of a bulb is the result of moving electrons through the filament. If the light were an LED, then the only way to get it to Emmitt light is through the movement of electrons. While the force that is moving the electrons is magnetic, I have a hard time believing that we could have electricity without movement of electrons. This is why I think people are having a hard time with this, I know it is the cause of my confusion.
@@Gyzome Not its right. Without electrons you don't have the field. The field happens as a consequence of what the electrons are doing. Not the other way around.
As everybody who's had to fight their way through differential equations knows way too well, there is a steady state solution, and a transient solution. Neither of these is right by itself, so ignoring the DC current (the steady state solution) is a fatal flaw in Derek's explanation.
I'm being a bit nitpicky, but steady-state and DC are not the same. Even in oscillating systems (AC) it is relevant to consider the steady-state and transients independently, as there will be some transient behaviour observed when flipping a switch to an AC supply, that will not be seen when the system is again observed long after.
Wrong! Derek’s explanation is also correct for DC steady state. Energy is transmitted to the load outside the wire through the field, even in DC steady state.
I am a High School Science Teacher. So, I am glad you pointed out that Veritasium failed to put the Unit "Meters" after the 1 in 'Answer D'. Their original 'Answer D' was "1/c s". I am always telling Students: "Write Your Units! [or it's just wrong]". However, what you did not point out, is that having the "seconds" there in the answer is also incorrect. Since the Units of "c" [Speed of Light in a Vacuum] are already "m/s", when you divide your 1m by it, you get an answer already in Seconds. Then if you multiply that by Seconds again, you get an answer in "Seconds Squared". So actually, "D" becomes the worst answer, because of its incorrect units. And without putting in the meters, like they actually did in their video, it would be even worse... "Seconds Squared per Meter". Even if the other answers are not quantitatively correct, they are "better" because they at least have the units of "Seconds".
I'm a self learning PCB design engineer, haven't got around transmission line theory yet, vertiasium's video really confused the crap out of me, this video makes a whole lot more sense.
Look up and go watch some vids on transmission line theory. V's video was at best disingenuous for all the reasons that EEV talks about here. Take them slowly at first because you'll be dealing with everything E&M. But TL theory is the ultimate expression of EM theory and it rocks. And you don't have to understand the maths, just accept them as presented. TL theory is also the basis of waveguide operation, and both are essential at the high frequencies used these days on PCBs. Best wishes!
The video triggered me. I was like yes…what he says is true, but there is a trick here. Oh it’s a transmission line 300 million meters across and only one meter long. The old physics trick of assuming ideal conditions, and drawing the problem differently to throw us regular folks off. Thanks for the explanation, I needed the refresher…have not done drift velocity since 2nd year, and attempted maxwell equations since 3rd and 4th year of engineering school. Great video for us out of practice EEs
I am wondering thought, what does ideal conditions imply? Does it imply that the impedance is zero? Wouldn't that also mean that the capacitance and inductance of the wire must be zero?
Derek claimed that the light would come on after just nanoseconds. That means the length of the wires past the first few metres is irrelevant due to causality. So if he is correct, he is talking about a transmission line a few metres across and one metre long. Certainly not enough to turn on any bulb I'm aware of. And he directly implied in the video that this was directly testable with actual "power lines".
I’ve never been convinced that Veritassium quite knows what he’s talking about. You explained it WAY better than he did. He just did not convey the thought as well as you did. Veritassium seems to sensationalize things, I think. I sometimes wonder if he understands as much of the subject as he thinks he does. Good work, Dave.
Yea I think he's more concerned with generating more comments and views than with explaining the concepts clearly and concisely. Which is too bad because I really believe Derek started his channel with the intent to help people learn, but now it's become all about pleasing the algorithm.
@@onjofilms well that kind of sensationalism surely works for easier to impress teens and novice adults but to me it's been a while since I've watched on of his videos just because it's more edutainment than properly educational.
Ah, but you must keep in mind the over-riding objective: to get clicks and views so you can enjoy that "sweet youtube money." (Quote from ElectroBoom, the all-time champion of sensationalism, and who, incidentally, is also an electrical engineer.) Give credit where credit is due!
Saying “correct” is a little up one’s self. Saying “I agree” places your knowledge and experiences in science ( challengeable) I enjoy your channel and knowledge sharing, thx for the efforts.
As a total uneducated person, I appreciate your explanations. Some of them really help me understand topics, while quite a few opened my eyes already. Thank you for your understanding, which leads to our understanding, thank you a lot!
Electricity is really simple to pick up but bloody hard to master. You start of with comparing everything to water pipes. Valves are switches, water pressure is voltage and the volume equals current. And that simple comparison works for almost everything an electrician needs to know. The biggest difference between the run of the mill electrician and the layman is that the former is supposed to follow code. It only gets interesting once you go either really small or really large. When frequency and distance becomes an issue or electromagnetic fields get powerful enough to warp your conduits. That's were the fun stuff starts.
Agreed that EEs are taught about drift velocity but I remember this was in an 2nd year intro to device physics class which some EE's do not take. Consider that many EE don't even learn the basics of transmission lines (my own undergrad experience). The Poynting vector stuff was definitely not taught to most EE because that would probably be 3rd year advanced E&M and on the physics side of EE.
For me E&M was mandatory 3rd year. Every EE student at my university had to take it, and a lot of them failed because it was really hard. I still remember one of the questions on the midterm was just "Derive the Poynting vector." I studied my ass off and still got a C in that class.
@@rsm3t -- It depends on your definition of the word "taught". I taught my pet goldfish calculus. He really couldn't sit still, but I'm sure he was a good listener.
So, the energy will reach the bulb through 1 meter of space, by the means of capacitive coupling, way before the far ends of the wires start conducting?
@@nukularpictures Depends on your transmission line impedance. Or the easiest explanation: The closer the wire, the bigger the capacitance and the smaller the inductance so more power on the first transient. And by "the closer the wire" I mean that you keep the light bulb and battery 1m apart but just move the wires so they kinda look like an L shape.
For the first 1/2 second, the result must be the same as though the circuit was broken at the far ends, because there's no way for the Derek/switch/load system to know whether those wires are actually connected.
@@allesklarklaus147 shouldn't it also depend on the Switching Speed? A simple Click-Clack Katschunk switch should have enough contact resistance for a 12V Battery to have a smooth enough turn on ramp that you won't see anything at 1m distance. Not even thinking about the horrible response time of a lead-acid battery in high frequency application.
"Every engineer is taught this!" .. Yes, we are. This video is pointed at those who didn't go into engineering and only have high school understanding of how it works. Which you said. So repeating it over and over doesn't help.
Not to mention I may have been taught it, but it sure doesn't mean I remember it, lol. Feels a little degrading to be repeatedly told "every electrical engineer knows this!" I didn't know/remember it, so I guess I'm not an EE. :( Should I tell my boss or have Dave do it?
Nice overview, with a few "footnotes": - "signal" and "power" transmission is no different. Even in a telegraph system, the S/N ratio is calculated by accounting for the "signal power" (meaning, there is no signal without power). Of course, some concessions may be made at 50Hz, as opposed to 2.4GHz; nevertheless, when crossing the Atlantic, even for 50Hz, the characteristic impedance of the cable plays a big role, and cannot be ignored. - the CircuitLab sim does not account for inductive coupling between L7:L8-like pairs. I had called-out the "dimension mismatch" on Derek's vid, btw :) Nevertheless, I think Dave overestimates "most engineers" :p
from what i understand there is a significant difference between signal and power transmission(even ac power transmission) as with power you will just have phase shift and power loss. but the signal will be completely distorted due to the different frequencies it contains(square wave). and when looking at dc power transmission it's completely different(but I don't think anybody would want to do power transmission over such a telegraph cable)
@@clemenswalter1984 Yeap there is a difference in the 50ohm and 75ohm cables, were 50ohm cables transfers more power, and 75ohm more voltage. Meaning one cable transmit and one for receiving.
32:00 "that capacitance at time 0 is a short circuit" that was genius, this really drove the point home for me! finally i could understand this properly! if you analyze the problem very slowly at steps of nanoseconds this makes so much sense! thank you!!!!!
It is short because at t=0 you have a "infinite" derivative (a dirac delta) on the voltage between the capacitor terminals and therefore its admittance for that infinitesimal instance t=0 will be infinite. In simulation you see this effect discretized to the minimum time step that is 1us.
As a physicist, it's interesting the difference in how we care about the fundamental concepts while engineers only care about whether its practical or not. Lots of stuff are totally unimportant when it comes to building practical things, but are conceptually interesting and important to understand. I haven't had time to see the Veritasium video in detail yet. But generally his videos are not about practical engineering or trying to teach engineers something new they didn't know about. It's more about teaching the general public about interesting and sometimes fundamental concepts in how physics work. Sometimes these interesting effects have no important practical effect in the context discussed, yet those familiar contexts are often a good place to gain understanding about them. (I have only skimmed these two videos, so excuse my ignorance if I've misunderstood something. I just found it interesting, from a physicists pov, that at the end of the EEVblog video above, I felt Dave was essentially saying that concepts that do not practical engineering value aren't worth mentioning. Which I totally get from an engineering perspective, but as a physicist we rather love these subtle unintuitive effects that are easy to miss since they have little practical value.)
I think you'll that with many fields in science/engineering. Many physicists don't really care about concepts in pure mathematics either (and misuses them... but hey it works :shrugs: )
Exactly. I find it irksome that this gentleman is harping on the fact Veritasium's video is not new science. Who ever thought it was? It's an explanation of known physics aimed at a general audience, and a rather enlightening one at that.
THANK YOU SO MUCH! I found his video on one side extremely detailed, and on the other side just ending in a dull statement without any real life explanation which effect causes "energy transmission" over the short distance. It starts with physics end ends with mysticism. Thank you so much for this video!
Physicists love spending time on debating the "correctness" of different interpretations that lead to the exact same end result. The current flows as a result of the fields and the fields induce the currents in the conductor. They are not mutually exclusive concepts, in fact, they are coupled and cannot be analyzed independently, therefore being both essential parts of the description of electromagnetism. In addition, that circuit can, in fact, be described in terms of more conventional circuit theory, but the effects of propagation would be modeled by discrete components (inductors, capacitors) or, in a more complex approach, with a transmission line. Those models won't tell you the value of the current in every single point of the wire and, consequently, nor will they give you the value of the fields around them, but they can model the value of the current in the wires over time at some points of the wire (e.g. near the source and near the load).
@@interestedparty00 Yeah, it's basically a transformer until the circuit "knows" it's been completed, as far as I can tell You'd get the same effect if the wires were infinitely long and disconnected from each other
@@interestedparty00 Couldn't agree more, completely misleading and confusing. The problem can be solved with the most basic laws of electromagnetism, but he makes it sound like some unknown physics concept that has many practical implications.
@@interestedparty00 you still don't get it, you need to rewatch veritasium's video and EEVblog , they both teach that , contrary to what you claim, most of the energy is traveling outside of the wires
My biggest issue with Derek's illustration is that he ignores the density of the fields. All his pointing vectors are the same magnitude and therefore the viewer is led to believe that the energy flowing through the air is just as big a contributor as around the wires. In reality, voltage applied to a wire induces an electrical pressure wave (E field) to the electronics spreading out at essentially the speed of light. As each electron reacts to this pressure wave, they are pushed or pulled. As each electron is accelerated, it induces what we refer to as a magnetic field, which is a model that shows the effect that the movement of that electron has on all the surrounding electrons. What frustrates me about Derek's explanation is that he seems to imply that the wire is inconsequential. This is absolutely not true as the wire houses all the electrons in a very mobile state that allows the E field to get them moving to allow the creation of a B field. In addition, field theory shows that the density of the B field is highest right at the electron moving and drops very quickly as you move away, therefore the pointing vectors should be very "thick" right on the wires and get much much less consequential as you move away from the wires. As Derek setup the problem, he is correct, the light will flicker 1/C s after you close the switch, but only due to the capacitive and then inductive coupling of the wires, full power will take much, much, much, much longer due to the transmission line Dave discusses taking a very long time to settle out.
Exactly. On one side, Derek was talking about magnetic field around the wire responsible for transmission of energy, and at the same time he was forgetting who is creating that magnetic field in the first place. As the Dave said, it is disingenuous to miss these details.
When you say inductive and capacitive coupling of the wires, are you saying that one wire is a transmitting antenna and the other a receiving antenna? Because if that is the case then Derek's video seems like a pedantic waste of time and he seems like a snob since as this video points out, everyone who (needs to) know(s) about wires radiating EM waves already knows that the amount of energy transfer across the 1m space is not the full energy and might not even be enough to actually power the bulb. Also, the simplifying assumptions are ridiculous and do not match the conditions under which he turned on a real light.
This & Mandeep's comment get it right. The way he talks about power transmission (in real life) in the same video, implies the energy is carried by that electromagnetic field *between* the wires. In reality, it is carried by the electromagnetic field along the wire -- not over the air directly to the lamp. In his example, the circuits with the switch and with the lamp would not need to be connected to get to the same result he did; that is, if you only care about the energy carried over between the wires through the air in 1 m/c.
"The light bulb has to turn on immediately current passes through it" "That's fine" No, it isn't fine. If you do the calculations, even roughly, there is less power going into the light bulb due to the antenna effect than a moth's fart. It definitely will not light up the bulb.
I totally agree with you that the induced flow of energy "due to antenna effect" in Veritasium's set up is so tiny due to the low voltage of the battery that it is not going to light up the light bulb shown in his video. However, if the wire is assumed to have zero electrical resistance, the light bulb would light up due to flow of electrons inside the filament (no matter how slow they flow) pumped by the battery but not due to tiny flow of electrons due to antenna effect. Besides, the battery provides DC. For the antenna effect to work continuously, the power source needs to be AC. Veritasium is not very smart to accuse people of lying when they say the light bulb lights up because of the flow of electrons when that is in fact the case.
@@chaklee435 Is it an "ideal" wire with no RLC - or are real world LC applicable? 300,000 km of wire with resultant massive inductance? Good luck when you open the contacts (back EMF)!
@@simon6071 Alright I'm bored, let's dissect your comment. 1.) of course the setup would not light up any real lightbulb. That's not the point. It's a physics thought experiment, not an exercise in engineering. Any current will do. If you'd prefer, we can contrive a lightbulb that works to our specifications. We can arbitrarily define how much visible light is required to consider the lightbulb lit. Then we grab an incandescent and heat it up in an oven until we are exactly on the line of not being lit. Then any current will tip us over the line. 2.) How is it that you are able to imagine millions of miles of wire with no impedance, but not a lightbulb that lights at any non-zero current? 3.) Why do we care that whether the antenna effect works continuously? The question is when the bulb is lit, not when the bulb is lit continuously for some amount of time. 4.) I'm no electrical engineer, but it seems that the fields are able to explain more phenomena than electron flow. That's makes fields technically correct, the best kind of correct ;). It's not lying to correct people on mostly useless technical points. 5.) The point of the whole thought experiment is to engage your intuition, and show that it is incomplete. I presume you have watched at least 2 videos on this topic, and still decided that your intuition was right the first time. Please don't get into politics, thanks.
@10:30 "a piece of restive wire" and "the battery" are mixed up. Even with DC the poynting vector always points out of the battery, because the E-field around the battery is reversed compared the the E-field around a resistance, whereas the direction of current ist the same in both cases.
Love how you did a "I'm not worthy" when Derek introduces Maxwell. That guy was the real deal. And then, you did it again for Poynting who should really be in the popular pantheon but for some reason isn't. But I do have to add Dave that Derek's video is most certainly not aimed at 'Geers and hopefully no physicist "learned" anything from it except maybe how better to explain it!
If the energy flows in a field surrounding the copper atoms that make up the wire, then the wire must act as an inside-out conduit or guiding line. Energy can flow without wire (radio waves etc.) but the wire (conductor) acts as a facilitator or focusing agent. This brings to mind some questions about the physical aspects of the wire. If you compare the electrical qualities of a Kilo of copper in the form of an ingot or a pile of copper pennies or a line of copper wire or any other form you may imagine each different physical embodiment of one kilo of copper will have unique electrical qualities. This makes me think that wire may have been one of the world's greatest inventions.
You may not be able to touch that electron directly, but you're still moving that electron, and that moving electron is still the source of the 'energy'. Put some reversed magnets in a tube as a stand in for electrons. You can put energy in by crashing other magnet's fields into the ones in the tube. The momentum energy is IN THE MASS and momentum of the magnet, even though the way you get it there is indirectly through the field. The energy goes through the field and into the magnet, and comes back out through the field interactions. At no point is the energy just 'sitting' in the field somehow, that is merely the mechanism of interaction to get it into and out of the magnet. You may get the energy into the electrons by way of their field and be able to do that both inside and slightly outside of the conductor, but the energy is very much in the momentum and voltage levels of the electrons. Those fields don't move themselves, they aren't an independent energy holder from the electrons. Realize for electrons in a conductor the real 'energy' is in lifting the electron sea away from their preferred ground state. If you have trillions of electrons on a conductor, and add a billion you've raised the state of all the electrons. That's why you can connect a path anywhere along the conductor and the electrons will deliver energy into the load. While you can get energy in and out by way of the field, at no point is the energy stored 'in' the field, it's sourced and sinked into that electron sea energy level. 'Energy can flow without wire (radio waves etc.) but the wire (conductor) acts as a facilitator or focusing agent.' Realize when you do this, you've done specific things to 'use' the energy in the wire to 'make' the radio energy. You've done a conversion process, it's not the 'same energy' just moved off the wire. In a way it is the same energy, in a way you've used one form and generated another. If you use muscle power to raise water to the top of a hill, are you thinking of that potential energy stored in the raised water as the same 'muscle energy' that was in your arm? Similarly in a way it is, in a way it isn't. But in both cases, it's not really just 'directly the energy you originally had' moved to a different place, there's a very specific conversion process required, not just 'energy went from here to there'..
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Watching this video and hearing "This is nothing new for engineers" leaves me disappointed with the professors that we had way back at the university. These concepts was not discussed in this captivating manner. In opens up another view to see the world of circuits. I commend the comprehensiveness of your understanding on this topic. It's like I found a missing piece on a jigsaw puzzle.
An extra video with extar comments for those trying to simulate this: ruclips.net/video/lBycH31K-E8/видео.html
How do people in Australia call it, exactly: Khrushchov's law or Kirchhoff's [ˈkɪʁçhɔf] "Kirk-hoff" law (K. circuit law, K. circuit rules)?
Both videos (Veritasium's video and Dave's analysis) are very interesting. But I still do not understand why we need wires in real life. From both your and Veritasium's video I understood *if* the energy would be transported along the wire with the speed of light it would take more time than if the energy takes the shortcut (direct path) from the battery to the bulb. His and your experiment show the bulb turns on faster than a "signal" could travel along the wire. So "why do we then even have to have a loop? Why are two separate parallel wires not sufficient to turn on the bulb?" If we need a circuit only because we need some current: use two separate circuits. One wire connecting plus and minus of a battery and another circuit with the light bulb. Both loops close to each other. Now if I would try this with a battery and a light bulb I am sure the wire in the battery loop would get pretty hot and the light bulb would not turn on. Or maybe it would be super dimmed. But if I set up a conventional circuit with battery and bulb in the same loop the bulb would shine brightly.
Now, for very close distances, energy can be transmitted "contact-less" (as used in wireless charging of e.g. smart phones) with high efficiency. I think I even (partially) understand that some sort of dampening makes the wireless energy transfer over large distances inefficient, but not impossible (I think any radio wave is transporting energy). So for "large" distances (e.g. already just a few meters in a house) we need wires to transport the energy. We cannot use a small loop with a bulb at e.g. level 2 and an energy source at the ground level with another loop. We need to connect both with a wire in a loop. But why do we need the wires if the energy is not transported along the wire?
Thank you for this explanation. Two observations:
1) "Disingenuous"... Derek made a "clickbait" video and is smiling as dollars are transmitted into his bank account.
2) You address the crux of the controversy at 37:37 in your video... The power transferred at t=3x10^-9s is "naff all"... The bulb would not light... Derek lied.
Again, thank you for making your response to a "scientist's" fake science video in which he works very hard to deceive.
Next up: Veritasium demonstrates that smoking is good for you!
@@slowhornet4802 Wires are needed because they lead the electromagnetic waves where to go. If two wires go to the moon parallel to each other, one meter apart, then the bulb would be lit up one second after the switch turns on. Because the distance between the electric generator (battery) and the bulb would be a little more than one light second.
@ You should look up time domain reflectrometry, and see how transmission lines are modeled.
You haven't described your scenario. Is the bulb on the moon at the end of the parallel wires (a balanced transmission line) with the battery on Earth? Then it will take about 1 second to light.
Or are the bulb and battery each on the Earth, each connected to their own end of the wires, then the circuit is closed between the bulb and battery? In that case, the bulb gets current right away and a wave begins travelling down the transmission lines to the moon.
How bright the bulb is depends on the resistance of the bulb versus the characteristic impedance of the wires. And it will take about 2 seconds for you to find out if the other end of the wires are short or open.
"a huge part of practical engineering is ignoring maxwell's equations". Exactly, we are busy reading datasheets, lol.
And finding replacements for non-available parts. 😭
@@MetalheadAndNerd it seems the preferred sport lately... sigh.
Its like everything else... you simplyfy to the most usefull system. Calculating magnet flux inna Electric cricut is pretty much impossible.
But when doing magnetism you have to do it of cause.
Worth adding... this is actually whats limit current in a super conductor.. this fact was discoveted fairly recently
Surely 90% of modern electronics engineering is knowing the exact thing you need but surfing RS, Digikey and Mouser trying to find what it's called?
As an electronic engineering student I had lectures about all of this, but I didn't really make the connection that power is always transmitted through the fields. I understood it at the special case of the space between capacitor electrodes, but never generalized that idea. Veritasium's video and your explanation to it flicked a switch in my brain. Thank you so much for that!
Well, fields carry energy, but the fields are generated by the moving charges .... its a question what is first, the chicken or the eggs .... claiming one or the other does something separately gives bad pictures ...
I'm a non engineer, but I want it to click in my brain, too. I'm gonna keep watching this vid and others. I just can't focus that hard, and there's some whoosing going on.
Telling about Elektro that way makes it easy to understand how a primary and secondary coil Work.
Have a nice Day and
Greatz from Germany
opo
its not electrical engineer? electrical and electronic is different
For his light bulb in a field idea to even work on pure field propagation you would need a tesla coil to create a high enough field strength at operating frequencies to light the bulb "wirelessly".
You still need to take into account impedance, dielectric, conductivity, angular propagation, reflections, and you'll arrive at a speed of propagation and VA required to operate the circuit
The simulation he performed as well assumes the capacitors have a static charge*(steady state) from T-0. if they were discharged you'd have to calculate the time constant in an LRC circuit based on the characteristic capacitance of the circuit.
Before complaining this video is too long, use the timestamp bookmarks to jump around if you want to.
lol too long?! Its only 45mins
So, basically, the energy will reach the bulb through 1 meter of space, by the means of capacitive coupling, way before the far ends of the wires start conducting?
@@elyeryan8838 Correct. You can also model it as an electromagnetic wave over the same distance if you prefer. I just like the capacitor model.
Also, C'mon Dave, this isn't Tiktok, longer more detailed videos are _preferred_ here.
Ok , there is to many timestamp bookmarks !
Lol !
Excellent analysis, Dave. I’m reminded of Physics and Chemistry classes at school: “So class, remember how we taught you about X last year? Well that’s not entirely true, so let’s look at what really happens.” And then a year or two later they do it again, and peel another layer from the onion. Makes complete sense as to fully understand the topic would just be too much, so we start with a simplistic explanation and slowly head towards the truth…
And in some cases 30 years later it turns out that even the last version at university was wrong.
@@spot997haha - and the culmination of all:
everything boils down to philosophy + spirituality (..or so)
or,: matter or hardware don't exist - only consciousness, waves & software
Than again, introducing particles instead of waves and talking about this weird thing of particle-wave duality, which is not only hard to understand but also plainly wrong is the bane of physics. There are ONLY waves, there are NO particles. Those waves are sometimes so localized and symmetrical that we can approximate them with particles i.e. balls of marble, but that's NOT what's happening.
Physics should ban teaching about particles and just focus on waves from the start. Then slowly expand the wave model into the full description based on fields. There's just no place for particles in modern physics curriculum as it gives the wrong impression to people as to how things are and work.
This was one of Veritasium's first videos that left me feeling like didn't really grasp what he was trying to explain. Your video helped me actually understand more about the concepts being discussed here. Cheers.
Because I guess he didn't really grasp what the finer destails are about.
He left out well established concept like capacitance and inductance coupling between wires making the puzzle more mysterious than it really is. I speculate he (or his writer) left those out purposely.
ruclips.net/video/TttHkDRuyZw/видео.html
Watch that video from Eric Dollard it describes everything youd like to know
Trust me it is counterintuitive, you have to be ready to accept the change. Anyway, hope you will find the " Field " Way more comfortable after this.
at 13:07 the interviewee says: "People seem to think you are pumping electrons..." and Dave chuckles at the idea - "nobody thinks that". However, this belief is pervasive amongst non-engineers because this is what most of us were taught in physics at school. And, ironically, this belief is prevalent amongst astronomers and cosmologist, too, because they are constantly trying to explain the presence of magnetism in the cosmos (and our solar system) by gravitational spin and "remnants" - not attributing it to energy and electric flow because there is no evident wire to provide an electron "circuit"
I was smirking at that "nobody thinks that" aswell. Actually as far as i know this is actually what the vast majority of people think.
"There is this electrical current thingy that flows out of the wall plug and makes my stuff work."
I distinctly remember a faucet being used as a metaphor in my high school science textbook
Exactly, this is what I learned in school. Simple as that. That needs to change is my idea, it doesn't make things very clear if you go any further than what you were taught and what's really the point then to learn it in a bad way?
Maybe most people think it but I think it's a fairly common exercise to calculate the speed of an electron in a circuit and find out its slow. The chain model he uses is actually fair too but you need to be aware that the speed of sound in the metal is more like the propagation of the signal than the movement of the chain (we learned of virtual "phonons" as the equivalent to photons then never used the term again).
I learned that elastic collisions between the electrons and the atoms in the conductor is the cause of resistance/impedance. I guess this is actually wrong? How does the field model explain resistance?
Something interesting I want to remark is when you said: "is nothing new for engineers" . I thought I knew about the basics of current (and I'm an electronic engineer) and honestly, during my time in the university, no teacher told me about the pointing vector (I remember a teacher mentioning it once, but just as a little mention, and honestly I am not blaming anyone) and seeing this to me is really new and honestly opened my mind on how do this world of electricity works.
Excellent video Dave!
Indeed. The Real World(tm) works with real world considerations, not fancy, complicated, thought experiment math models. Stretch out a million miles of super conducting wire and _prove_ it's 1(m)/c. Two wires 1m apart have f*** all for capacitance. (I've never even seen an instrument capable of measuring such a low capacitance.) The power did not flow from the battery to the bulb through 1m of open space. It's flowing along the wires, or we wouldn't need the wires in the first place.
If the battery has been connected for more than 1s, all of the wire has been "charged". Closing the switch at that point would, in theory, instantly allow power to flow. This is the "water pipe" equivalency -- once the pipes are filled, water can appear to flow miles away almost immediately. If that hose hasn't been primed, it's going to take awhile to flow.
This is the kind of physics experiment I'd like to see! 2ls of super conductor is hard to come by. If we do this with fiber optics (light/photons) -- and we have, this field theory math nonsense goes away. If you have 1ls of fiber, nothing comes out until 1s after you fire a photon in the other side.
@@jfbeam
Real world(TM) is too complicated to be able to usefully calculate the necessary stuff correctly. The way I remember an engineer decided to replace d/dx with a variable s and so his differential equations like you do your your normal equations. Mathematicians had a fit because it worked but there was no math to prove it true until Laplace.
I agree, my undergraduate degree in electronics glazed over a lot of critical theory under the guise of "you have to learn it yourself". It was disjointed and rather than focusing on the critical, fundamental theories they focused more on providing you with practical skills, which to be honest killed a lot of the joy in curiosity I had and I've been forced to learn and discover accidentally by myself, in my own time.
We had this in 11th grade at school. Very surprised it wasn't taught in under grad EE.
I don't know what university you studied at but this was in the first year electromagnetism module when I studied. (see Kraus "Electromagnetics" 1981)
I'm a retired Director of Engineering with my field in Electronics. I love your videos. I especially like it when you destroy scammers like Solar Roadways. I worked for a small defense contractor and I'm very aware of SBR's. There are people who take advantage of people's ignorance of science, electronics, etc.
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, the better model is a dipole antenna model. See my explanation in the main thread.
I’m so sad to find out that solar roadways is bullshit. I don’t really know anything about electricity beyond what I have to know to run my amplifiers, but that video gave me so much hope for the future. Makes me mad to think that people were just pulling on heartstrings.
My main objection to the Veritasium video was the implication that the electrons don't really matter. They don't carry energy, and look at how slowly they're moving!?!?! No, it's the fields they generate that carry energy. Well sure, but those fields don't exist without the electrons and their ever so slow motion. I know that he never would actually say that outright because he knows it's not true, but he leaned really hard into a semantic argument that got close. It's like saying that people don't actually buy things in a shop, no, it's their money that buys things. Well yeah, that's true, it's the exchange of currency that allows for a purchase (in most cases these days anyway) but it's the people who bring the money to the shop. They're not separable.
Thanks for this comment, I'm no physicist, but have had some college level courses in electronics, electricity, X-rays, and passed the first 2 ham radio license tests, and his video threw me off of almost everything I understood about electromagnetism.
This is the point I was grasping at, and it really seems like the two can't really be separated out from each other.
The moving electrons generate the electromagnetic field, and without electrons there would be no field, and no power.
Derrick showed the hosw/chain/wheel analogy which is a pretty good way to demonstrate how electricity works. I suppose the point of his video is that the chain is not representing electrons, but the en field. That means that the electrons would be represented by pulling the chain back and forth, and it seems that without the hands, the work isn't getting done.
@memyself I am not quite sure, but other science based channels state that the the magnetic field is intrinsically tied to the electronic field. These other videos state that they can't be separated, and just because the electrons themselves don't actually flow entirely through the wires like water molecules through a pipe, it is their change in state that results in the pulse of energy.
It seems like it similar to a wave in a rope, we can hold one end and move it up and down to create a wave. The rope molecules don't actually travel down the rope to the end, where something may be happening due to the waves movement, but no one can argue that the wave is a result of a change in the rope's state.
This is how it seems electrons are used to produce electricity, we charge the electrons on the wire, which causes a chain reaction in the adjacent electrons, creating a wave.
In any case, from what I have gathered, the charge generated at 1m/c is due to magnetic induction from the battery side, similar to how a transformer or wireless charger works, only at a greater distance. This makes sense and matches the physics I learned about electricity. If you know of videos that explain something different happening, please post the links.
Most electrical engineers have a hard time graduating from DC to RFM microwave. In fact all of electromagnetism everywhere in the universe it's an AC phenomenon any DC electricity is simply electromagnetism where the frequency equals zero, so it is it is an extraordinarily isolated case. And to an extent the electrons and the fields are quite separable: just consider the entire radiation field of the sun which contains a practically infinite (but not infinite, simply integrate the Planck distribution) spectrum of frequencies propagating outward, some of it intercepted by the earth. Anybody on the earth can measure the intensity of the field at any given frequency...when so doing where is the electron?
@memyself I follow your explanation right up to the last where you say, "Current flow is not energy flow." Since current requires electrons to move and they can't move without an E-field, and once they do move, there is an M-field generated.
40:24 - Feynman showing that "the Poynting vector" is going into the wire: This is not the entire Poynting vector that represents the energy flow from source to load. That part that goes into the wire represents the losses in the conductor. We strive to have good conductors - the better the conductor, the smaller the electric field in the axial direction of the conductor and the smaller the component of the Poynting vector pointing into the wire. When integrating this component of the Poynting vector over the surface of the conductor, the result is I*I*R.
There would be no voltage drop on a wire with zero resistance, so the electric field in axial direction would be zero as well and there would be no bit of the Poynting vector pointing into the wire. All the energy would remain in the field outside the wire.
Great comment!
Yes, it's actually weird that from the basic stand point of conservation of energy, one can so casually keep saying that the Poynting vector, i.e energy flow (flux) is towards the wire (and keep assuming a lossless wire). Dave makes it seem like it has something to do with the energy flow along the wire. (or that's how I understood him) But how would the energy the propagate to the load if this is the only direction of the Poynting vector?
Actually I think transmission line theory for this problem is even more complicated than just imagining it as two dipole antennas. Well .. if antenna theory is any easier to understand.. but intuitively you would see why the energy travels near instantly to the load -- because they are two dipole antennas next to each other.
i watched how powerlines were being repaired using a helicopter, and was given some explanation as to how this was possible without getting electrocuted. seems the electric field was diverted around the helicopter so that the cable could be repaired.
Dave mentions about this at 11:18
whatever Feynman said, that is the truth. He wrote a fucking book about quantum electrodynamics.
and a lossless conductor could therefore be infinetely thin?
Pointing vector goes into the wire IF and only IF wire has resistive losses, otherwise the tangential electric field on the surface of the prefect conductor is zero.
Component of the pointing vector flowing into the wire is the resistive loss.
The component of pointing vector along the wire is the one carrying the power to the load.
The DC electric field inside the bulk of conductor is proportional to the resistive loss!
That's Poynting
@@milos_radovanovic Finally someone gives the right answer.
Most wires which I have encountered in the real world (I am a physicist by training) have resistive losses, even though I have made experiments at an electron synchronton with superconducting magnetic coils once.. but even there most cables were actually standard, resistive copper cables.
Yeah. The poynting vector in fig 27-5 at 43:00 is the energy flow that is converted into heat.
Very valuable pair of videos. Kudos to both Derek and EEVBlog for appealing to general audiences in order to explain the magic of electromagnetism but also to confirm to RF engineers what they've been doing for decades, which itself is a confirmation of the physics behind electromagnetism. The physics behind electromagnetism is lucidly and brilliantly explained in the textbook Electrodynamics by Melvin Schwartz first published in the late 60s. Basically the entire field of Electrodynamics rests upon a solid underpinning of Einstein's relativity and the fact the the Electromagnetic field is a 4D Invariant Tensor, not some combination of 3D vectors. In addition, ohms law is an approximation based on the assumptions made about the drift velocity of electrons.
Well done
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, the better model is a dipole antenna model. See my explanation in the main thread.
Cool, now let's calculate the time it takes to light up a bulb if the 300k kilometers of wire was laid out in a perfect circle. ;D
The problem I had with the veritasium video was, that some real life problems (resistance) are waved away, but others (capacitance) are not but not mentioned - and this feels like it is deliberately misleading. Also Derek should have mentioned that the layout of the cables is very important. This way the correct answer depends on effects that he made me ignore with the introduction ("we have to simplify this")
He acts like many bad teachers do: He creates an environment where his specific statements are true and leaves out the factors he had to set up to make his statements true.
BTW: I'm still curious why we need thicker wires for powerful applications if the power is not transmitted inside the cable anyway.
@@MetalheadAndNerd Well he said he has to ignore resistance :) I mean then it all works out that way.
Have you ever taken a physics course? Problems are always simplified in order to focus on the principles of the subject at hand, especially in introductory courses. When, for example, you are first introduced to capacitors, you ignore edge effects. You don't use Jackson in a first-year physics course.
Imagine a different layout: a almost planar (X - Y) figure 8, crossing point distant 1m in the Z direction and the lines on the crossing plane in 90deg. The capacitance is minimal in this case and the battery and lamp will be 1m apart. If Derek is right, that the power is not transmitted over the cables, but over space (air), the lamp will turn on the same way, right? MAKE A F# EXPERIMENT! He could do it with relatively simple equipment, like an oscilloscope and differential probes. Very disappointed with Derek...
@@michaelsommers2356 yes, but normally you say what you simplify but pronounce the effects, that you are going to focus on... instead of mystifying them to "totally blow you mind"
30:00 It's actually an important fact, that initially it doesn't matter if the circuit is closed or not. If that made a difference it would enable faster than light information transmission, which in turn, would spin up Einstein to really high rpm in his grave.
What I wish there was more discussion of here (especially since it's something Derek got so into in the Slinky Drop series) is a difference between how quickly the information that the switch has closed gets to the light bulb, and how long it takes to actually light up a practical light bulb, and for how long it would stay lit, etc. Like, I can grok the information getting there, but how much power is in that brief spike Dave showed in the simulation? Not much, I should think. Enough to even light a red LED?!???
What if the bulb was at one end with everything else the same?
Yeah, 1/c ! LOL
@@manojlds interesting question. Since the potential of the wire opposite the battery should initially be between the between those of the battery terminals the Poynting vector goes outwards in both directions during the first half second. That corresponds to the energy invested into charging those "capacitors" the two parallel wires on each side can be considered as. Another way to see it is as energy invested into building up the electromagnetic field between the two wires. There's an electric field between the wires due to the potential difference, and a magnetic field around each wire due to the current.
At most that can expand outward from the battery/switch (let's keep them together) along the wire pairs with light speed at most (when/where air acts as a dielectric medium between the wires it's likely a little less). Another way to look at it is as a signal (like a step function) traveling along a wire pair, and where it has been through . When the electric field hits the end where the wires are short circuited that wave is reflected.
This reflection of the wave at the ends where the wires meet depends on whether they are connected, and e.g. if there's a light bulb between them.
See this for the difference between those resistances:
ruclips.net/video/zrDxSM91Jcg/видео.html
It'd be interesting to do a version of the experiment with just two rolls of twisted wire pair, like the one in the video.
It's about at that point that I'd need to consult some physics books and maybe do some math to get beyond hand waving and really see what happens.
I think the wave traveling back puts both wires on the same potential, effectively unloading the part of the capacitor behind it and the Poynting vector from the battery outwards is cancelled. This travels past the battery, the Poynting vector on the load side then doubled, as the other wire is then on the same potential as the terminal on the closed side.
On the bulb side the impedance of the cable pair and the resistance of the bulb will probably be important, else we have some kind of reflection there too.
If it is matched, then the bulb is lit with half voltage when the 1st wave arrives (1/2 s after the switch is turned) and with full voltage when the reflected wave arrives (1s later, so 3/2 s after the switch is turned). But I'm really guessing a bit here.
I honestly also don't know how the thickness of the wires comes into play, because that affects the capacitance, inductance and impedance of the wire pairs. There are impedance calculators for twisted wire pairs, according to them wires with 1mm thickness would result in an impedance of about 1k Ohm. This (and the battery voltage) should determine the amount of initially outgoing current after flipping the switch (at that point the current can't be determined by the resistance of the light bulb at the far end.
I'd also have to look into the "no resistance" thing. The dampening effect usually helps to make such systems well behaved. Maybe it's enough to assume an inner resistance of the battery (and of course the light bulb). Setting the whole system up without any resistance at all (just a closed loop) probably results in an oscillating system.
Einstein was covard and hypocryt.. He even try "exorcixm" at quantum entanglement.. We have confirmed Bosson.. Specialy his TAU what is confirmed fasther than light.. Is just opening another layer of physic onion.. If you cry after you remove skin.. You shut not be a coocker
My personal problem with Derek's analysis is that (as can be seen from your simulation), the "ON" state of the lamp lasts only a couple of miliseconds. I don't consider this to be actually "ON". Particularly in a video aimed at general public (i.e. not electrical engineers / physicists), no one would consider this to be ON. For something to be consodered ON in this context, it has to stay on (steady state). So, the answer is not 1/c. If the question was "when will you see a voltage spike across the lamp in the transient analysys of the circuit?", then the answer would be 1/c
What he doesn't bother to explain, is that it isn't just the fields close to the switch that are at play. After the switch is turned on, there is an immediate step in the voltage at the wire, which gets coupled to the other wire. But also, that step is moving toward the right over time, such that for the whole time that voltage step is moving to the right in the lower wire, it is coupling to the upper wire, and takes a while to get back to the light bulb. So the whole time the pulse is traveling to the right, there is energy being transferred to the upper wire. This continues until the pulse turns around at the end, returning on the upper wire. The result is that there is a (near) instantaneous low-level lighting of the bulb for one second, followed by a brightening at the one second point. At least, this is how it works if you use a random size of wire and a random light bulb. But because the pulse is losing energy as it propagates, if the wire (actually a transmission line) and the bulb are properly matched, you won't see a change in brightness because the pulse that had to travel the whole distance will be at the same level as the current that was induced as it traveled to the right.
@@BrightBlueJim Are you saying that if the transmission line had been perfectly matched to the light bulb in Dave's simulation, then the voltage and current would be constant after t=0 rather than instantly drop off? Is it even possible for the transmission line in Derek's hypothetical experiment to ever be matched to the light bulb?
@@ncmaothvez Yes, that's what I'm saying. Almost. There's still the 1/c delay that the pulse has due to the 1m spacing between the wires. and yes, after around 3ns, the light bulb goes on, and stays on at a constant brightness.
At least, that was what I thought. Turns out I was still wrong, though.
At first, I was thrown off by the 1m spacing, because I'm used to much smaller dimensions in transmission lines, so I thought that the impedance of the line would be very high. But then I "ran the numbers" and for a reasonable range of wire diameters, like 1mm to 10mm, the impedance is actually around 500 to 1000 ohms. Using an on-line calculator for transmission line impedance, because I'm lazy, I find that making a twin-line transmission line out of 2mm wire, we get an impedance of 828 Ohm. For a 120V light bulb to have a resistance of 828 ohms, it would have to pass (120V/828 Ohm =) 145 milliamps, which would make it a (0.145A * 120V =) 17.4W light bulb. This is close enough to the 16-17W of a typical "100W equivalent" bulb to work.
But NOW I realize that there's still a problem: the transient solution to this problem - what happens when the switch is flipped - puts the transmission line's impedance in series with the bulb, which results in half the voltage being dropped across the transmission line and the other half across the bulb, which Derek alludes to in his video. BUT, the steady-state solution - what happens when the transient electric field has faded out because both wires eventuailly reach the same potential - drops nothing, due to the hypothetical zero-ohm wire, putting the full battery voltage across the bulb. So I was wrong about that - even perfectly matched, the bulb will come on at half-brightness for one second before it abruptly rises to full brightness as the initial switch-on pulse travels around the loop and reaches the bulb.
I don't just know this from theory - I worked for six years in high-power microwave pulsed RADAR systems, which use a modulator that incorporates a set of inductors and capacitors to make an artificial transmission line that operates much like this circuit, and the amplitude of the pulse IS pretty close to constant over the time it takes a pulse to travel through the transmission line and back. So the transient solution isn't just a quick spike caused by the capacitance between the wires, but a pulse whose length is twice the time delay of the transmission line.
Isn't electromagnetism fun?!
@@BrightBlueJim I've got to admit that my analog electronics theory knowledge doesn't reach very far beyond ohm's law and a crude understanding of transmission lines but I was still able to follow along in your explanation. Thanks for the reply! This got me curious, need to read a bit about transmission lines tomorrow when my brain is a bit more awake :) Yeah, I'd never have guessed the impedance would be as low as sub-1000 ohm's.
Exactly. This spike would happen even if the circuit is not closed. And we don't call that "ON". Yes, you generated 0.00...001A in it, but you don't need 2x300000km wire for that...
The ON state means at least that you can differentiate the current from the case when the circuit is not closed. It would be still a low current, but also at least .5sec...
This video was beyond my expectations, I literally learned a lot thanks so much for sharing all this
Thank you Dave, this video provided me the information that I felt was missing from the Veritasium's video. I've studied civil engineering, not electrical engr and also I have my amateur radio certificate so this helped me link the transmission line theory into all of this. I've come to realize that there was something missing from my understanding of how all this works, I guess that I need to pick up some books on Electrical Engineering to complete my understanding.
I'll try and find these Feynman lectures, Thank you very much again for completing the picture of this for me. :)
Careful! Dave here uses the wrong model for Derek's experiment setup. A transmission line model is not applicable, so what you see on his graph is incorrect, and Derek's answer of 1/c for immediate steady ON is also not entirely right, it's misleading. For the immediate transient, the better model is a dipole antenna model. Also, Derek conflates DC steady state with transient analysis which is false and folks who want to learn, get misled. See my explanation in the main thread.
You're making a lot more sense than the original video. The Veritasium video seemed to imply to me that the existence of the wire would be irrelevant over that distance. Of course, it's evident for short distances that the wires don't have to be connected to transfer power, with for example transformers. But the details concerning thickness, resistance, distance, power , ac/dc, etc. matter a lot, otherwise every device and circuit would interfere with each other and be practically useless.
It seems to me like Derek tries to make concepts appear to be as counterintuitive as possible instead of trying to explain the concept as clearly as possible. I might be wrong that he's doing this on purpose to generate more commentary/discussion/views, but the end result seems to confuse more people than it does explain the concept clearly.
I would argue that the original video is wrong. The reason being that the magnetic filed is made by moving electrons. The field is just breaking the electrons from moving att full speed.
@@Kanglar , I think so. He throws the baby out with the bathwater, so to speak, by making a technically correct explanation seem as though it has no value. There are different levels of abstraction that can be made for various phenomenon and those all can be correct. I found his video good, but slightly misleading because of that.
hmm is the wire sort of is irrelevant because you don't require a wire to transmit power..
There are a number of mediums that can transfer power...?...
The surface charges are already along the wire. When the switch is thrown a current is created, making a B field, now power can flow through space. As real wires have resistance, power also flows into the wire where it is dissipated. It is not bad to say that the only purpose of the wire is to allow a current and the role of current is to make B.
40:24 What's missing in Feynman's Fig. 27-5 for the steady state is the electric field component perpendicular to the wire due to the charge distribution in the conductor, which together with the magnetic field makes a Poynting vector (and therefore energy flow) parallel to the wire. Feynman's figure only shows the electric field component due to resistance, which causes some of the energy flow along the wire getting directed into the wire.
This also means that most of the energy flows outside along the wire, not directly through space from the source to the load. I would argue that answer "B) 1 s" is therefore closest to being correct since only a small amount of energy due to transient effects arrives at about 1m/c.
With regards to fig 27-5, are you saying there is non-uniform charge radially in the conductor at steady state DC? Is this not what Dave was talking about re skin effect? Or is this another caveat?
@@Aor87 I am talking about surface charges in a DC circuit. This is a different concept than the skin effect, the latter of which only occurs for AC currents. Surface charges seem to be an often ignored detail when people talk about DC.
Think of Veritasium's circuit with zero-resistance wires. In steady state, the net electric field inside the conductor is then zero, but there is an electric field on the outside of the wire coming from the surface charges. This field contains the energy, which is transported along the wire. So while it's true that the energy does not flow inside the wire, it still flows mostly close to the wire where the electric and magnetic fields are the strongest with a Poynting vector approximately parallel to the wire.
As member of general public: when I finished viewing veritasium video, the first thing I thought was... "Ok, then if I put the bulb into a Faraday cage, the cage would block the electromagnetic field that comes through the air and the bulb wouldn't light on". And thats absurd. Therefore, it would be quite more complex. If I haven't misundertood you, your explanation saves this problem. Thank you.
Actually at exactly 40:24 they measured exactly 6.9 level Earth quake on the magnitude scale at Altadena, California. The first responders at the scene found that the source was Richard Feynman's grave, where he had been turning violently. The cause was later determined to originate from an EE misquoting him.
@@dbenitopperez Faraday Cages only work if there are no holes (especially no holes with wires going through!) Yes, if we connect a no-holes faraday cage ( REAL faraday cage) around the bulb, it will short out the bulb, there will be no EM fields inside the cage, and the entire current will be across the outside of the faraday cage.
Thanks!
The "low frequency" "circuit type" engineers do not necessarily know the transmission line details. I can remember talking to a digital design engineer that I worked with at IBM, who had graduated from Cornell, and I was trying to tell him about how a step function can bounce off the end of an open circuited transmission line and the voltage will double... so a 10 V step can produce a 20 V voltage for a time... and he would not believe me.
unill he gets emc problems
@@mattmurphy7030 Did I say otherwise? I think you read something into my post that I did not say.
Well, a degree does not prevent from being clueless…
He just probably never had any experience with RS485 lines, never connected an oscilloscope to the lines at different places and newer given the question of spacially distributed elements of the circuits enough thought. Just give him some time, reality tends to enlighten us once we lose any way around properly facing such a problem in a design and have to understand what is going on.
Many other small discoveries are awaiting him along the way as well! Like having a voltage between different "grounds" or magic changes of voltage levels, magic 110ohm load from even an open twisted pair and many others. I am even a bit jealous. I wish I could experience that one more time.
@@Kirillissimus he just thought that Kirchhoff's Voltage Law always applied. He thought that you cannot have a 10 V voltage source creating a 20 V voltage without a negative 10 V voltage somewhere in the loop. He said "you don't know what you're talking about, you are obviously wrong." There was a bit of "I went to a better school than you and you're out of your league and claiming ridiculous nonsense since you don't know better, and I do."
I think the visualization is a bit misleading, giving the impression energy basically moves directly between origin and destination as long as there is a physical connection "somewhere". They have the yellow energy lines looking like they are completely independent of the physical path of the conductors (esp. the ones going straight from battery to lamp perpendicular to the wires). If there was something [impervious to em fields] blocking the straight path between the battery and lamp the yellow lines would not be as "neat" and would more conform to the shape of the wires - which also changes the permeability of space part of the formula he only mentioned quickly at the beginning.
The visual model was impressive but quite messy. i actually mentioned that in another take I did that I couldn't use before I goofed the system audio setting.
Sure Dave, blame the audio system. It's always the audio system's fault, isn't it.
The wires control the current and the current makes B. In this way the wires influence the power flow. The Veritasium video shows power along the wires, something left out by almost every text book ( well physics text book, I don’t expect engineering texts to do any better).
It seems that if you screened the battery and wires with metal foil the lamp never lit. Not really my experience actually.
@@mattmurphy7030 something like that
I get the feeling his video might leave the general public with a poor understanding.
As an engineer, I hadn't thought about how large a portion the surrounding magnetic fields was compared to the amount of power in the wire. But I also work mainly on batteries and motors, so nothing over long distances. I would have thought no more than 10% of the power flows outside the wire, but maybe it's more.
Pretty much. People gloss over the spherical cow in a vacuum type assumptions required to arrive at the conclusion, then try to to apply to reality. The more closely an equation is to mimic reality, the uglier it'll get.
Didn't you say that Grant Thompson from the king of random dying in a accident was his own fault and then change your channel name to hide from the backlash?
Yeah, as a non-electrical engineer Veritasium's video made me think I had missed something, but it's just the small amount of capacitance between the lines that lights the bulb. Seems there was a lot of missing information from the video that will leave people without a full understanding.
I think you're right, and it's not hard to figure out who will be most affected by the misunderstanding. We have an environment right now where people are going crazy for no reason over 5G -- literally tinfoil hat kind of stuff. If they start thinking that all of their power plant energy delivery is coursing through the space between their ears instead of hugging the wires, who knows where it could lead :-).
Take a look at his entire channel and try to figure out who is audience is. His audience is primarily the slightly-better-than-averege layperson for the topic of the specific video. His example of what he used to teach students looks very much like a High School explanation, not a University Engineering explanation. His explanation in this video is explaining nuances that I didn't learn with my 2 year degree in EE Technology, so I would say that his audience for this video is anyone who is interested in electricity who have a 2-year degree and less, not someone who has a 4-year EE degree...
Great Video. As someone who always kept asking "why?" and "how exactly does this work?" during physics classes un school, i am a bit disappointed that people aren't taught this. I know it's easier to look at it as if the energy is flowing through the wires, but nobody ever teaches the "true" version. Amazing to finally understand this. Now will it help me in any way? Probably not, but i love understanding the universe more and more.
Let's throw away wires, who needs them when energy trawels without 'em.
@@barnabaskiss2 😏
Coax wires are no "true" wires as energy travels completely inside, they should burn.
If energy doesn't travel "in the wire" - then why does the wire increase in temperature when a current flows ? - Try connecting say a 9kW shower with thin wire... and see what happens!!
Or - does it suggest that there is a "resistive" part that heats the wire... and the transmission in energy outside the wire can be thought of as a "reactive part" - ie dissipates no power..?
@@eric4709 Right. Of course the majority of the energy will actually travel IN the wire and not outside it. What most people seem to forget is that the em field also follows the inverse square law. So the further you go away from the field source (i.e. the moving electron), the weaker the field gets. So the majority of the actual power transmitted is inside the wire. Otherwise when you close your hand around an insulated wire and all the energy is transmitted outside the wire, 99% of the energy would go through your hand. However since there is no conductivity where actual electrons can enter / leave your hand, you do not get shocked.
Technically EVERY macroscopic physical interaction is the em field or gravity. There are only 4 fundemental forces in nature and most of them are the em field. So while the weak gravity from earth pulls you towards the center of earth, it's the em field of your molecules that repell from the molecules of the ground. "Atoms" do not actually collide when you hit a solid surface with your fist. It's the em field of the atoms which repell each other. All of chemistry is only about the em field and the interactions between atoms and molecules.
So technically the example with the metal chain, it's also the em field that is moving the chain and transmit the energy through the chain. How do you think do the chain segments "collide" with each other? Right, the em field of the molecules. So I don't get why everyone is so hyped about "yeah it's just the em field and not the electrons". That's just not true. Without the electrons you don't even have an em field. Also think abour the spatial power distribution in the field. Everybody knows magnets. Same inverse square law. If you get further away, the effect quickly becomes unnoticable. So this whole "any amount of power" (which was later added by veritasium) is complete nonsense and distorts the actual thing you want to explain. If the question was "when would you notice that the switch had been turned on at the light bulb?" everything would be fine. The amount of power that is actually induced on the other side is very small. So we're not talking about transfer or power but just signals / information.
So just to be clear: Probably 99% of the power is transferred INSIDE the wire through the em field. The drift velocity of electrons changes proportional to the strength of the field which is also directly proportional to the current. In the veritasium video it sounded like the electrons move very slowly at a constant rate which is not true. It's directly related to the current. Yes, in AC we have no net movement but that doesn't change those facts.
If it would only matter what happens outside the wire, why would it matter what diameter the conductor has or what material it's made of?
I don't get why so many directly agree 100% or 80% with Derek. The way it's presented is just misleading. When I pay a house and I say "I'll pay it tomorrow" and I plan to pay only $0.2 every day, can I claim that I have paid for the house? Technically yes, but practically no.
17:13 if an ethernet cable is submerged in water, or if its casement is flooded, you will have noticeable attenuation in the transmission. its specific enough that Fluke has a cable tester that can detect if a cable is submerged, and how far down the line the fault is. as far as i know, Fluke engineers have the patent on that. i happened to meet one of the Fluke engineers working on this problem, and he did his testing with a big plastic tub of water next to his desk, and a coil of ethernet cable in the water lol
As a member of the general public: when I finished watching Veritasium's video I have gotten the impression that faster than light communication is possible, because i missed that the exact arrangement of the wires is important.
Thanks for clearing this up for me, I might be interested in learning more about this as a result =]
the important question for me is what happens if someone cuts the cable at one of the far ends (150,000 km away), how long would it take for the bulb to turn off? it certainly has to be 1/2 second, because otherwise the information that the circuit is no longer closed would be travelling faster than light.
But if the cable was cut before closing the switch, you could close it and see if the bulb turns on after 1 m / c seconds. If it doesn't then the information that the cable is cut traveled faster than light.
So how can the circuit "know" that it's complete in just 1 m / c seconds
@@_invencible_ Electromagnetic induction? The wires close to the battery and those close to the lightbuld are just one meter apart, the lightbulb and the battery are just one meter apart. The switch is close-by too. Flick the switch, cause the electromagnetic fields to change, cause electromagnetic induction between those close by wires, power the light bulb for a bit.
But, without making any calculations, which I'm not even sure I could make, I doubt the energy transferred would be enough to actually light up the bulb, especially at 1m/c time.
=RNGFN= _Invencible_ Well the electrical engineering answer would be that it does not matter if you cut the wire before closing the switch because the energy capacitively couples from one part to the other, just as shown in dave's video in his simulation. The lamp would turn on and eventually turn off once the transient is over. The time it can stay lit would depend on the actual capacitance between the two wires and the impedance of that light bulb and some other stuff like inductance in the wire. (well, keep in mind that with real components it might never actually light up..)
Hope this helps and isn't too complicated for somebody with no EE background.
@@allesklarklaus147 yeah but what if you take a whole chunk of the cable so there's a large gap between the ends?
=RNGFN= _Invencible_ Okay, I think I got what you are thinking about. The capacitance I am talking about comes from the fact that there are two wires laying 1m apart for 150.000km long ends. I am not talking about the capacitance at the point where you cut the wire. While that capacitance exists, it would be so small compared to the wire-laying-1m-apart capacitance that it is irrelevant.
Veritasium is very much geared towards the layman and gives good insights to the more interesting aspects of science while leaving out the details. I think he steeped over the line when he mentioned that there are lies taught to us in school. There aren't any lies, just simplified versions of science that match the current understanding of the student. So unless you study engineering or physics at the college or university level, then all you have is the simplified version. I like the conversations that have been brought up from Veritasium's videos recently.
Veritasium is doing more lying than any school teaching this subject. The schools are teaching this more accurately than Veritasium is doing. Sadly, Veritasium is outside his area of expertise about this topic.
I one heard Neil deGrasse Tyson describing it as "teaching on a 'need to know' basis", as going into full detail would just overwhelm any student and would take way too long to get to the actual point at hand.
So you start with the most simplified high level view, leaving out a lot of stuff first, and then start adding things back bit by bit.
That "leaving out the details on a 'need to know' basis" can be considered lying in a way, technically. But it lacks the intent to deceive that would be needed to make it a real lie.
@@hartmutholzgraefe I also like the explanation of the need for these kind of primer "wrong concepts" in the Science of Discworld:
“A lie-to-children is a statement that is false, but which nevertheless leads the child’s mind towards a more accurate explanation, one that the child will only be able to appreciate if it has been primed with the lie”. An example: teaching the nucleus of an atom with electrons going around it like a mini-solar system in clean orbits in order to later teach the electronic cloud model.
Agreed, in fact his video itself leaves out some details in order to simplify this issue. Perfectly acceptable.
If you watch some of his recent videos about RUclips and clickbait, he probably does this on purpose - he knows how to play the RUclips game and something about "the lies taught to you in school" or "the truth about electricity" etc. is going to get more clicks than a bland sciencey-sounding title about EM fields.
12:53 remember, Dave. “Most people” are “not electrical engineers.” The speaker is absolutely correct.
I agree. Most people would learn the lumped element model in school and that is the end of it.
And Veritasium is a physicist and not an engineer, it is just a difference on point of view. The information is correct considering the simplifications.
And therefore the 1st explanation is the best one for us idiots or this idiot anyways this extra stuff you're adding is more confusing than the 1st 1. Otherwise you need to be in a form that's for the professionals not the idiots like us or me anyways.
I am delighted whenever I hear engineers who are rigorous and show a proper understanding of the fundamentals down to a sufficiently low level for the topic at hand. Unfortunately, in my anecdotal experience (that is in no way a proper statistic) very few engineers care or are knowledgeable of the underlying science behind the practical equations and models. Also in my anecdotal experience, it's only the engineers who do care that make progress in their fields, either as researchers, designers, developers, or troubleshooting and optimization.
For these reasons, I subscribe to engineering channels like this one and enjoy their content so much. Great work, Dave; thank you for the content!
Heh fields
As a computer engineer, we focused more on the practical side than the theory side when we covered electricity and circuit building, and this was news to me. (It's possible we glossed over this in class and I don't remember but we definitely never went in this much depth). This was rather counter intuitive to me and my mind is blown. I love that I can be this wrong, the more I learn the less I know. Thank you for the knowledge and praise Maxwell!
Same for me. I don't understand Dave's exasperated "WHO THINKS THAT?" followed by "All engineers know that". He keeps on answering his own question: the rest of the world. Veritasium is not aimed exclusively towards engineers. Actually, I'd say its rather the opposite. Derek never claim that this is unknown. Just that it's a common misconception, which I can bet everybody's asses that it is.
Yup same!
Same for me. I'm also an amateur electronics enthusiast and I learned something from this and Derek's video.
If you had taken power systems engineering (I had one semester) electromagnetics, or RF design (which requires the previous as prerequisite), Poynting vectors and fields in general are thoroughly dealt with in those courses. Computer engineering blows past a lot of fundamental engineering. I was an embedded systems and instruments guy myself, the computer engineer in me was developed because of market conditions, not coursework. Although I had 1 graduate course in computer architecture and 3 courses in C/C++ years later in community college.
This is the vibe that I got from the Veritasium video too; not wrong, but a bit sensationalist, not sneaky, but avoiding certain key elements in order to get wants out of the audience, and the physics perspective all the way.
The presentation of the video made me feel like he didn't really have a full understanding of the physics himself.
the target audience isn't engineers, he can't list all the factors otherwise it'd just become engineering/physics courses.
we can add temperature and so on...
@@alexisfrjp Anybody who isn't angry about the details of this video clearly isn't an electrical engineer and even as an engineer from a different field I find it a nice mental model for my dumb ass brain.
Yeah, veritasium is mainly doing things sensationalist these days because he's mainly after view count. He genuinely wants to spread good information, but he realized (and said in another video of his) that he HAS to make it sensationalist because that's the only way to survive on youtube and make money.
He could have mentioned Parasitics.
Also that his circuit uses a ideal lamp and battery uses a super conductor and it's in perfect vacuum.
24:10 as an electrical engineer myself, *THIS* is the main issue I have with this video. It tells people that _"all energy is delivered outside the wire"_ - which will make them wonder if their electritian is trying to sell them unneccesarily thick/expensive wires, as the energy does not go "through" them.
A followup video diving into this would be super interesting I think. :)
If they employ an "electritian" I think that would be the least of their problems! (MY spell checker changed it to "electrician"!)
The Veritasium video is spectacular. Revealing to the general populous how electricity actually transfers energy is not going to make people magically stupider. Wire sizing is a thing, and I'd suspect more people are aware of wire gauges and amperage than they are of Poynting planes. By explaining to them how the fields carry energy simultaneously while the electrons inside the wire flow, I don't see where anyone would get so confused that they begin second guessing the electrician they hired regarding anything he suggests.
Thanks Dave for your unagitated and professional and way reacting to this.
I see the point made on the veritassium video, however for the general public and the average guy, it's like considering Einsteins relativity theory every time using a GPS.
Side note: My flux capacitor equations never gave back 42, maybe because I neglected this fact we have learned now. Jeez...have to do it all over again.
If you divide 121 by 42 and then subtract 2 and multiple by 100 you get 88. Well, 88.095 but the digital speedo was only two digits.
GPS only works because of both general and special relativity. The fact that we don’t need to understand these subjects to use GPS does not mean some of us need to, and for the rest it is cool to know the deeper truth.
@@jimmcclymer4230 Do you actually have a credible source for that Einsteins relativity was needed to develop GPS. I have read somewhere that the corrections for relativistic effects are done with calibration parameters on the clocks that are determined empirically through measurements rather than through theoretical calculations. I know that it is often stated that relativity theory was needed in the development of GPS but to me it makes sense that you would just measure any drift in the clocks after launch and compensate for it. From a practical point of
view it does not matter if the drift is due to relativity or if the clocks just got out of calibration during launch.
@@mattmurphy7030 Yeah but he does that kind of in a way that purposely misrepresents physics.
@@Kandralla Yeah it annoyed me - he's structured the video like a 3 card monte to generate controversy, comments and clicks rather than trying to explain the subject in an understandable way... And he does know how to make good educational videos when he wants to.
My biggest beef was the as considering the tiny voltage that you get through the air as "lighting it up" it basically destroys the concept of circuits to me.
Any source that you hold technically lights every single lamp in the world because the electromagnetic field has infinite reach.
"People seem to think that you're pumping electrons"
"No one thinks that! Who thinks that?!"
...
Me, before Derek's video. 😝
You are, obviously, there is electron flow and hole movement. It's just that that electrical charge flow is VERY very minor.
For those who understand this short documentary, daily life will turn upside down: The Connections (2021) [short documentary] 💖
Almost every one who isn’t in the “field” thinks this way. Like high way’s cars go in one direction and then back. It may not be correct but I bet the most outside the “field” visualize it that way. BTW why has his video clip gotten so much reactions? (The question is more in general, not to this specific post). :)
“Derek is correct” But the reactions point to “bloody murder!!”. Not specifically a comment on this specific video or channel (actually this clip was pretty balanced and good by me). But where is all the reactions coming from? Seems like people haven’t had a shit in two weeks and finally find a toilet.. ;)
Yep! 99% of the public probably think that (myself included) - which is who Dereks videos are intended for. He's not trying to teach an electrical engineer something they most likely should already know.
I am an industrial electrician specializing in industrial automation. The examples he gives and the lump theory that he explains he thought is what electricians are tought in trade school. It's borderline amazing to me, as an electrician I feel like what I was taught in trade school is an incredibly simplified version of electrical theory to help get the masses out I'm the field pulling wire. I have increased my knowledge considerably since trade school but most electrician don't. Infact most electricians don't know what would be considered fundamental knowledge by most electrician engineers.
My biggest issue with Veritasium's video is that he makes it sound like the electron movement is essentially an inconsequential side effect of the energy flow outside of the wire. The battery isn't a magical device that contains vectors waiting to escape. The energy from his lead acid battery depends on the movement of electrons. Without it, the negative plate quickly builds up excess electrons which repels the negatively charged HSO4 ions and stops the reaction. The movement of those electrons is absolutely required.
@@KLRJUNE But one can't happen without the other.
@@KLRJUNE What carries charges in a wire? Electrons. The repulsive force between electrons will cause an increase of electrons per unit of volume on one end to propagate down and show up as an increase of electrons per unit of volume (and therefore increased charge) on the other end. This is why we don't have to think about drift velocity of electrons in electronics but can just think of the movement of electrons.
It's analogous to the air ejected from your mouth when you speak - it doesn't move very fast, but the local change in pressure propagates outwards at the speed of sound. Veritasium's argument comes across to me as "people think that they're hearing the molecules of air you exhale but really it's not air you exhale but the sound waves traveling through the air!" It's a pedantic point, and you can model sound just fine using the movement of air without keeping in mind that zero of the air molecules from the audio source may arrive at the detector.
@@KLRJUNE Yes, but he said it better (which usually means a few more words are transmitted).
@@KLRJUNE what you said sounds like you don’t need electrons what he said is that you need but they are not what Carrie’s charge huge difference hence no one got your point at first
@@KLRJUNE you said that the waves matter not the movement of electrons,
all iam saying is that the majority of people including myself reading it think you mean electron do not matter only the waves.
the dude above you explained it clearer, even if you meant the same thing we didn't get it. so iam glad he explained it in a longer way.
Derek did not give all the details of the wire used (other than "no resistance"), but for what it is worth -- one can model a parallel transmission line to develop the characteristics that may be usable in a circuit simulator. For example, if we assume the wire is 10 gauge and is separated by 1 meter (center to center), the characteristic impedance (Zo) of this transmission line is about 798 Ohms. The capacitance is about 0.04 pf/cm and the inductance is about 26.6 nH/cm (all assuming a dielectric constance of 1.0 -- free space).
When the switch is closed, the current that flows will be based on this surge impedance (x2) -- ignoring any lamp impedance -- until the sytems reaches steady state DC conditions. It is not going to be much current during this transient period: 12 Volts / (2 x 798 Ohms) = 7.5 mA ..... Doubt this is enought to light the bulb "instantaneously".
Boom, this is EXACTLY what I was looking for - thank you! The author of the original video conflates steady-state analysis of power with the dynamic step-response of the signal. Before the steady-state is achieved, the initial power delivery is only 90 mW. That would be
@@DeadCatX2 I think the power in the bulb would be even more minute because the cold resistance of the filament is about 10 times less than its resistance when lit. So the Veritasium video is wrong. The bulb will not light until the wave travels to the ends, sees the short circuit and reflects back to the bulb. He should have used an LED as that would light with 12V through 1.6K.
Yep, at this time a lot of people figured it out, that there will be current on bulb, but only small. Lets imagine, you have to have a substantial part of current of your sorce on a bulb to light, lets say, 10% of a source, and your light bulb would not light up on a AC coupling only in this case. And video makers keep ignoring this point of view, concentrating attention that we will have potential difference on a bulb.
This is a great analysis. I had imagined the two wires coming from the battery as an electric dipole and the two wires from the light bulb as another dipole, so it is (for short times) two coupled electric dipoles. Your analysis is a great back ofthe envelope calculation.
So at 0.04 pf/cm it is the equivalent of having two 12,000 uF caps in series with the light (ignoring resistance and before the current gets all the way around and it reaches steady state)
As an "IoT engineering" student I can say that you are wrong in saying "every engineer knows that". My course never mentioned that and It felt so weird to watch this video about something I thought I knew well.
Plenty of graduate students carry around this mental image, 100 %. You still can abstract it away because you just learn the idioms of... whatever you're doing, but getting rid of how you visualize already super out-there things (if you think of electrons, do you assign a color to them mentally and what do they even look like? Does anyone not have a picture of black holes popping when we're talking about electron holes? What about doping?) is really, really difficult - and possibly not even that interesting.
You just map your general understanding of a small problem to a unique visual (or sensory) landscape and that's how, say, "electricity" looks to you. It's almost a matter of language, as is so often the case - someone mentioned Mehdi's Kirchhoff battle I vaguely remember and as so often, it boils down to how you phrase a question, definitely something Derek touched on too and many other RUclipsrs. Most professional engineers and scientists are severely limited in terms of conceptualizing different aspects in novel ways, and we all can sympathize with the notion of just having learned one tool properly - why would I invest 5 more years learning another DAW when the one I used for the better part of my life is almost part of my brain at this point?
Elka?
Can confirm this. As an Embedded Systems Engineer, in college our focus was mainly on digital systems and software. Our electronics class pretty much peaked at calculating capacitor and inductor phase shifts using complex numbers. Saying "every engineer knows this" is a bit unnecessary, because not every engineer is concerned about this aspect of electronics, or electronics at all.
@@Bllinker No proste że tak
@@smolus0512 Przyps xd
Thanks Dave for letting us hear your insight on information videos, always appriciated!
I quite literally design transmission lines, and the whole time I was watching Vertiasiums video I was thinking to myself "yes but....." Generally, it's not really a useful way to frame things and it's clearly just for the 'wow' factor that it gives a general audience.
As a physicist, I agree with you that this is not at all useful for day to day work, but it is cool. Typical of what we do in physics to simply the problem until it is beautiful - Oh and we got to the beers long before the engineers! (Although if I had to solve it I would treat it as a transmission line!)
like all veritasiums videos.... 🙄
@@morethan4mph finally a physicist, thank God
Why doea it happen faster than the speed of light? I mean, wth, the information that the switch is closed shouldn't be capped at the speed of light to travel across the wire (or around)? Like, current, EM field, gravitational field waves, ain't *everything* capped at c?
@@mildlifeisatrisk5727 it happens at the speed of light.
@@morethan4mph oh, thank you for responding! :)
But wait, if it happens at the speed of light, and the wire is one light-second long (or the half of it we'ee calculating on) shouldn't it take at least one second? 🤔💭
(Supposing everything is ideal, super disclosable, don't oscilate a bit to establish, etc)
It's all about models. If you want to derive the ideal gas equation, your atoms or molecules are tiny billiard balls. If you want to explain the Rutherford experiment your atoms have a positive nucleus and negative electrons. If you want to explain the Chadwick experiment then the nucleus has neutral particles as well as positive ones. And so on. In electrical theory, electric current flowing in wires like water in pipes is a perfectly adequate model for explaining what's going on. You choose your model to fit your purpose.
Also, Dave, thank you for mentioning the Feynman lectures on physics, that being available for free online made my day! I foresee many hours spent by me reading that stuff.
The youtuber "AlphaPhoenix" decided to actually do a physical test of the thought experiment in their video "I bought 1000 meters of wire to settle a physics debate". AlphaPhoenix also did a follow up video expanding on further questions "Why does WATER change the speed of electricity?"
What a fascinating 45 minute rant. As an engineer, I love it because I can so much relate to it. (However as a mechanical engineer, I deal with different misconceptions)
I'm glad you cut the wires off at the ends in your little example.
They were always just bait to make things messy and confusing and him putting them there just rubbed me the wrong way.
Your explanation with no bullshit (although you didn't really say anything particularly new to me either) was very nice and clean.
I guess everyone needs to define what 'on' means. For Derrick's answer, 'on' is any minute power dissipation in the lamp (and his answer is correct for that definition), but my first reaction is that 'on' is the full power dissipation allowed by the impedance of the lamp, and the power source. This version of 'on' is not reached until the EM propagation is allowed to travel through one half of the circuit. Before t=0, another assumption can be made that circuit is in state with the switch closed, meaning that the entire circuit is at the same charge between the left side of the switch, and the same charge on the right side of the switch. That EM charge is unfolded at the speed of light after t=0 and the light goes to full 'on' once there is a positive charge on both sides of the lamp (ie c times half the circuit length).
This is what confused me at first too, especially after he had all these EE guys talking his claims up. The lightbulb is probably already "on" just from random background charges moving: no power source needed! His explanation is not really what most people think of when they think of "on".
Perfect observation. You should be a Mathematician (if you’re one not already) or a good philosopher that seeks Truth above all else. 👍👍🤜🤛
Exactly! The whole topic is ill-defined. It is basically impossible to do any useful lighting (even if ignoring all the effort to make the element inside the bulb to start to glow) before 1 second.
This is the first explanation that makes any sense. In a pedantic and nitpicky sense, the moment the switch is closed, changing electric and magnetic fields propagate from the battery terminals and its adjacent wires, to the bulb and its adjacent wires; but this power transfer is incredibly weak, and may not even cause a single photon of light to be emitted. Derek assumes that one photon DOES get released immediately after the switch is closed, calls this the "ON" state, and drops his mic.
There's got to be a better way of teaching Poynting Vectors and EM power flow to kids, without causing this level of confusion, which is based on an impractical technicality. Maybe replace the DC battery with high frequency AC source, and have the target bulb be something that can be usefully energized by that source. I'm thinking of something along the lines of the "fluorescent bulb lights up by itself near high voltage AC lines" demos have been around since forever.
Thank you for this video. I am not an engineer, but an electronics and ham radio hobbyist for about 45 years (and biologist). I like how you explain the different perspectives of engineer and physicist, and allow for the differences due to intended audiences. Usually it is not required that analogies be totally faithful and descriptive of reality, if they provide some increased understanding! I will keep studying the physics, and the transmission line theory, but I will also keep building stuff like 9:1 unun to allow me to use non-resonant wires for my antenna systems. I am often having fun with other people's designs. In our radio groups are some retired electrical engineers and I am always so amazed at how they build stuff based on their OWN designs. Wow! Keep having fun learning, and (if you are so inclined) building stuff! Both can be VERY fun. Dave WA4NID
I have to point out the comment where it was said that “everyone knows this,” when referring to EEs. I can’t speak to physicists, but I can tell you that if I asked my colleagues at work what drift velocity was, even just at a high level, they would scratch their heads in confusion. Some might say “oh, I believe we learned that in General Physics in undergrad.”
Well it depends on the field of study and working environment obviously. I'm studying mechatronic engineering and we do see quite in the details the physics behind semiconductors in various courses about design of electrical control for motors for example, but we've done drift velocity during the introduction to "electronic & electrical motors"
This. 99% of the population probably has never heard of any of this and at best thinks magic electricity (maybe electrons) is being pumped through hoses (wires) in to the end device. Among engineers: would bet an EE knows this, but probably not an ME (short of some elective class they barely remember). Physicist: same thing, depends on the type. Virtually any other major is probably shocked to hear the answer.
@@wileecoyoti Drift velocity is basic undergrad physics every physicist takes.
@@whuzzzup if you dont use it, you forget it and it is berried in the void :)
i agree. i asked some engineers and physicist. the physicist knew the drift velocity speed roughly but didn't really understand the answer to Derek's question.
the electrical engineers didn't know the drift speed and when presented with the answer to dericks question was "Sure if you say so"
i certainly was not taught propagation speed or drift speed in my formal education. I worked out the propagation was roughly speed of light when i started working with transient situations and always assumed electrons moved very quickly but less than speed of light. that was interesting to find out but frankly arbitrary
You said all I'd have liked to say. Well explained! He implies the bulb turns on, as in "it turns on normally (100% power), and remains on" and that is clearly not the case! But yeah... the physics are ok.
Yeah, I didn't go into the wave and reflection response as the video was already long enough.
@@EEVblog You definitely should) Need a few seconds of bulb brightness simulated and graphed under this model
Yea, Not including dimensions is really irritating and potentially blocks people from understanding. Nerd click bait, lol
The physics is totally wrong as he assume the bubble start emitting light instantly as the electric energy is fed to it. Sory it's wrong, that bubble first need the switch mode converter to stabilize then the decoupling cap to charge up before the LED start glowing !
And if you want to get picky about what happens in terms of reflexion in the line, although that will only account for a super tiny irrelevant fraction of the turning on time, then you must acknowledge that the damn PSU in those modern bulb is by no mean a "nice" resistive load as used in the calculation we made at EE university (That's why for more powerfull unit you need a prefiltering stage before the actual AC/DC converter so you don't mess up too much with the cos(phi) of the power line). Fact is understanding things at this level would be a mathematical nightmare and once again it doesn't matter as in the real world that switch to light time depends probably as much on that than on the noise.
So yes "assuming a perfect world that doesn't exist where everything would go according to the equation i want to demonstrate then the physic is right". To me that's an oxymore to say it's wrong.
Magic light bulb, the transient will be over long before the filament heats. I thought for a incandescent bulb on time is defined as 90% filament heat. If using a LED will it even get to forward voltage?
18:45 is honestly the most important part between actually useful content and garbage.
19:42 is actually the part I find worse... Since it is a video targeting popular science. It is generally missinformative even if it is technically correct if one accounts for the intentionally left out information. (36:50 I like to remind you Dave that the video is for the Regular Joe, not engineers nor physicists.)
35:30 yes if the circuit were a circle, then it is the diameter of the circle divided by C seconds,
But the thing that annoys me with videos like this is that they don't actually explain things properly. Leaving the viewer with 1 answer that is only applicable for the ONE example scenario. While not providing the viewer the answer to Why that answer is correct in that scenario.
So I will dread having to deal with people who from now on thinks it takes 1/Cs for any electrical connection to be established. Though, depending on the material between the wires, it can take a lot lot longer than 1m/Cs unless we do the setup in perfect vacuum. The speed of an EM wave in a material after all isn't C (it is dependent on the relative permittivity, also known as the dielectric constant), but that weren't even mentioned, despite being a major spec of most transmission lines. (Though, doesn't stop even experienced network technicians from believing that their fiber optic cables goes at 300 000 km/s, even if they typically only go at 60-75% of that. The dielectric constant of glass is fairly high.)
wtf there was no info left out. He literally shows the bulb & the battery 1 m apart
"While not providing the viewer the answer to Why that answer is correct in that scenario." he literally spent the whole video explaining why it is 1/c s
btw 1m/Cs is bad form for 4 reasons
1) 1m = mixing variables with units = confusion. If you want to write 1 metre it is 1 m
2) Never put units on the left hand side. It is a waste of time & it's mixing variable with units
3) it is not big C it is small c
4) cs is wrong. The correct form is number space unit e.g. 5 s not 5s
& c s not cs
& 1/c s not 1/cs
I'm sure others have pointed this out but a quick point about the 1/c thing, if you do unit (dimensional) analysis on 1 m / c = 1 m / 3*10^8 m/s, so unit analysis the fraction we get is m / (m /s) = s. So it is 1/3*10^8 second not 1 m / c second or whatever.
Ideally if we had a standard math function like absolute value but that was unitless value that turned a quantity in some units into a unitless coefficient you could use that. I'm not aware of such a function but taking a cue from absolute value function if |x| is the absolute value of x, let >x< be the unitless value of x. So >c< = 3*10^8 [where c is specified in meters per second].
So using that the answer d) should have been given as either:
1/>c< s
or
>(1 m /c)< s
or if your willing to let the reader do one's own unit analysis etc.
1 m / c [in meters per second]
or if you want to have a bunch of ugly number hanging about
1/3*10^8 s
Obviously unit analysis gets more of an emphasis in chemistry or solid state physics (personally I only passed stat mech by looking at a problem looking at the equations I had access to and figuring out how to Rube Goldberg myself from the set of units specified in the problem to that required in the solution), but it can trips us up almost anywhere.
There was a lot of missleading things in Derek's video, and it took me days to finally figure it out. I never had the same definition of "turning on" as he did. Sure the initial change is at 1m/c s due to capacitive coupling between the wires, but the lamp won't see significant power until it reaches steady state, 1s later. As Dave said, make the circuit a circle, or just seperate the two wires further apart and it changes everything. Derek's video should have been more about capactive coupling between two wires instead of focusing on EM fields. The topic had nothing to do with the quesion/answer. Very missleading.
"switching on" instead of "turn on" would have already made it a little clearer. Very missleading, since the lightbul won't be glowing at 1m/c s.
Even in a classical sense the light bulb would light up in 1m/c seconds because as Power = Voltage x Current. The voltage would as explained in this video propagate at the speed of light and the current starts immediately after the switch is closed so yeah it’s still 1m/c.
Glowing and being on are not the same thing, that's an interpretation problem (i.e. you), not an issue with the video.
@@parryhotter3456 'the light bulb would light up in 1m/c seconds ' You guys realize the lightbulb would really never light up due to power sources not being able to drive 300,000KM of line and deliver power to the bulb, etc..
By focusing on one variable and pretending the others are infinite and infinitely efficient, etc, the whole idea is like any other fake 1=0 proof. You're roughly accomplishing a multiply by infinity or divide by zero by calculating on the 300,000 KM lines when the reality is none of that stuff would be driven that way when you start taking the other variables into account..
IOW a 'Reductio ad absurdum' type failure, or really probably the opposite of that. Reduced to the point it still seems to hold up, but actually the failure has been hidden in the reduction of variables..
Start calculating all of this out with real 1 m loop numbers and real 300,000km loop numbers and it'll become a lot more obvious that reality isn't going to work this way..
You are exactly correct, the question is meaningless because of the assumptions that are made. The first being you can have a 0 ohm wire. The second being that we define the bulb as being ON when ANY electrons pass through the "bulb". Does some current flow through the bulb in 3.3ns, sure! Is it enough current to be significant, hell no! My hunch is that you would actually get way more current just moving the wire 1 cm/s through the earths magnetic field. And Derek's video either fails to point out, or he didn't realize that the bulb would turn off again almost instantly as the transmission line locally meets steady state, and would only turn on again once the electrical field has populated through the wire.
@@Kindo1085 If you had cared to read through the slides provided by Derek under his video, or if you had considered carefully Dave's lumped element model that places a capacitor every certain distance along the wire until half a light-second away, you would realize that the light bulb will not turn off almost instantaneously. The thought experiment is very meaningful to me. The assumptions help keep the video short and keep me focused: I was inspired by the fact that Maxwell's equation, the transmission line theory, and the Poynting theorem could all lead to the same answer!
Very interesting video even for a non engineer like me (I have a chemistry background).
I also think your point of the different mindset is true in every field. I routinely work with electronic density (computational chemist), while I have experimentalist collegues who don't give a crap about the nature of the electrons and deal with reactants and products. We all work within some approximation, otherwise it would take forever to do anything meaningful. It's important to know what's behind the approximation and realize when the approximation break down, but we can ignore it most of the time.
As a chemist i worked with plasma physicists and totally agree with ur points
At last a sensible understanding.
my wife is a german shepherd (i am hungarian and thats legal)
I've watched a few of Veritasium's videos and on the ones I know something about he always seems to leave out important information as well as being for people who don't know anything about what he is talking. If you know anything about the subject you probably already know most, if not all, of what he is talking about. And the answers he comes to aren't necessarily the best answers since they are ignoring vital bits.
If you go back and watch his other videos.
You will find some videos that deliberately ask questions and then don't answer them.
Guess where the answers are? Next video.
More views!! baby!!
I hated that kind video so much that I stopped watching a long time ago.
But lately he's been fishing really hard for viewing count.
Even though I clicked not interested, youtube kept pushing it to my feed.
So I clicked [don't recommend his channel]
I couldn't bear to watch the original Veritasium video. As an electronic engineer I baulked at the title. Thank you for sparing me. Your analysis was well done and saved me from that tedium.
Veritasium walks a fine line between thought provoking ideas and unbearable smugness. Ok maybe they don’t walk a fine line, they stagger from one to the other like a drunken scientist.
This reminds me to Ferreira's power loss models for conductors (used for estimating power losses in the windings of transformers analytically). There's a chapter in one of his books explaining how energy is transferred inside transformers and the problems to calculate the poynting vector in a real component analytically (as well as why the rest of the book is technically wrong but provides correct results). Definitely one of the most amazing engineering books I've ever read
Edit: I hadn’t noticed that the autocorrector had changed poynting to pointing
What's the book's title?
@@alpardal I think it was Electromagnetic modelling of
power electronic converters
@@dhombios thanks 👍
pointing vector is such a great inadvertent tautological pun XD
@@mycosys Sorry, autocorrector had changed poynting to pointing
This actually helped me better understand his video. Especially because the battery was DC and I wasn't exactly sure what was going on. The instant I saw your lumped element model I got it.
Thanks Dave!
The counter-intuitive workings of electromagnetic fields was actually what pushed me over to computer science from electronics. I had so many unanswered questions about why we were using the notion of current being a flow of electrons when it seemed flat out wrong after learning about electromagnetic fields. Turns out that it was just an abstraction (albeit a useful one), but I never "got it" back then. Still puzzled that my teachers couldn't explain this in a better. Mind you this was still at high school level (three year service electronics path), but in the end I felt that I was missing so many pieces of the puzzle that I just changed over to computer science instead when starting college. Very informative video, thank you very much.
when did you change majors? I dropped out of Chem before transferring to New Media. I was looking at a geology course' curriculum and like... I want to go back because it looks like they filled in a lot of holes.
@@illygah that's weird, I would think filling in the holes would make it harder to do geology
Interesting! Your understanding of the word abstraction has probably changed so much due to your CS education, you may not have liked that answer any more as a high schooler
A major difference in the way we electrical engineers deal with the practical aspects of electrical engineering is recognizing that a true STEADY STATE d.c. circuit ( no time-variant current/voltage changes ) there is no reactance, only resistance. There is no electromagnetic radiation from conductors in a true steady-state d.c. circuit.
Derek's video made it clear as mud... 🤔
The transmission line model makes lot more sense to me. Your videos are highly informative and fun to watch. Learned a lot from you. Thanks man!
It was SUPPOSED to be clear as mud. The objective of this video was not to teach anything, but to show how clever Derek is. He left out a lot that could have made it clear, I would say deliberately. He's trying to set up another bet, like the one he made with a physicist about the wind-powered car that could out-run the wind. And he's trying to get more viewers than he would just by explaining how this works. I've lost some respect for him because of his video.
@@BrightBlueJim He also done shillings for Waymo like it would solve traffic and reduces parking. But the solution is public transport.
Dave made me a EE! I am thankull for that! And see him talk about my area of work is just wonderful!
Thanks for the video and the analysis. Here are some comments:
1) You don't need to add 'second' to the answer when you say 1 m / c. C already has units, so the answer should simply say 1 m / c.
2) In your simulation, you simply assume a capacitance and an inductance for the transmission line and the simulation doesn't take into account the finite value of the speed of light. It seems to me that the simplifying assumption of the circuit is that the transient effects in the circuit are fast enough that the finite speed of light won't affect the result so you can simulate your circuit at 'infinite' light speed.
3) I think the initial transient pulse that the light bulb sees can be more easily understood in terms of radiated waves when you initially turn on the circuit. If I attach two short wires to a battery to form a dipole antenna, at the moment both wires connect to the battery, the wires would emit electromagnetic waves due to the square wave pulse. This can be then received by the same kind of setup with two wires forming a dipole antenna and a light bulb replacing the battery. The received signal would create a non zero voltage difference between the terminals of the light bulb. This doesn't prove that in the steady state, the power is transmitted through the air and not through the wires. The transient signal doesn't have anything to do with the steady state flow.
4) Since we are assuming any non zero voltage is enough to turn on a light bulb, when I do this little experiment I basically turn on all the light bulbs everywhere around the world. :)
I think he used "c" to represent _just the value_ so that answer would've been written as 1m/(c) m/s, which simplifies to 1/c s.
@@spidaxtreme That wouldn't be a common notation in physics since c is already defined with a unit.
@@couplingconstant it is in relativity theory; since c is used all the time, units are dumped out the window, and you see a 1/c appear in a temporal coordinate all the time.
@@takix2007 I'm not sure what you mean by that. Yes, factors of c or 1/c appear and they have proper units. Position four-vector is (ct, x,y,z) and all components have units of length, or four-momentum is (E/c, px, py, pz) and all components have units of momentum. In particle physics you often use natural units where you set c to 1 and change the definition of meter and second. Then you completely drop all the c factors from your formulas since you set it to 1. But that's not what we are discussing here.
@@couplingconstant indeed, that was exactly what I was referring to. And indeed it has little to no bearing to the discussion at point.
BTW, you surely meant to say that all components of the four-vector have the *dimensions* of lengths (which can be expressed in units of lengths, i.e, meters in SI) ? 😜
This is a deceptively simple problem with lots of rabbit holes to pursue, but Dave clears up this problem nicely. One of the most interesting classes I took in college was transmission lines in my senior year (BSEE curriculum). In that class the professor very clearly showed that electricity is really light, at least in terms of behavior, but I think even at a fundamental level. Even though this wasn't a class in optics, theories of refraction (lenses) , reflection (mirrors) and other topics were compared to transmission line equations and sure enough the parallels are amazing. Even a radar dish on a jumbo jet behind an "opaque" cone appears transparent at radar frequencies. The cone material is specifically chosen so the impedance is matched. If the wrong material were used the radar would be reflected back into the plane. Light is a coaxial circuit from source (eg an LED) to observer or destination (eg our eyes or a camera sensor). Our existence is a complex matrix of coaxial circuits that we take for granted every day.
I've looked at the two "expert" references in Veritasium's video, they are both useless. The first one produces a waveform with no timescale but is actually the short transient pulse as shown in Dave's simulation. It doesn't show when the actual dc power arrives. The second one does the opposite his analysis only shows the arrival of the 12V at the lamp and the reflections that result from an unmatched transmission line. He only shows the voltage at the lamp and so doesn't show the initial delay at all. It's easy to see how Veritasiuim has been misled by these analyses.
I agree with your observation as well.
"misled", or mastering clickbait
As someone that is not an engineer, it is definitely something very new.
Before Veritasium video, then your video and other video, I always thought that electricity is about stream of electrons moving, flowing from the power source to devices.
I thought the same about the flow of electrons being the cause of electricity, and I had to take a digital circuits course in college and took an electricity course as an elective.
I think one of the things I have trouble with is that the electromagnetic fields can't exist without the flow of electrons, and of course the flow of electrons can't exist without the electromagnetic force.
The thing about electricity in the real word is we have accepted equations, for example Watts (power) is equal to the Voltage times Amperage, and Amperage is a function of the number of electrons in the transmission medium. Voltage is equal to the current times the resistance. It seems to me that you can't have electricity as we define it, without a combination of the electrons and the waves.
I wonder if this is just arguing semantics, because in the original video Derrick says that electrons don't carry energy, but doesn't anything in motion carry kinetic energy? It almost seems like the argument is more about the fact that the electromagnetic field is the transmission medium for electricity, but we generate the field by moving electrons.
I I were dropping a rock from the top of a building, isn't the rock delivering the energy when it hits something, even though it is gravity that is the cause of that energy?
In the end though, it seems like movung electrons will always be required to make use of the electromagnetic field.
I thought Derek's video was the equivalent of a bright kid teasing another by poking them over and over while chanting, "I'm not touching you! I'm not touching you! Technically it's only the repulsion between the electrons in the atoms of our skin that's occurring, nothing is actually touching!"
Sure, it's correct, but also deliberately misleading. It feels like Derek's video was made to appeal to those who want to have knowledge to be more correct than others, rather than to be able to use it usefully. I was left more confused after watching it, and I don't know how much educational value it would have to someone even less familiar with electricity fundamentals than me. (I assume Dave's talking specifically about electrical engineers when you say "all engineers know this." It definitely wasn't covered in the single circuit fundamentals course we got in mech eng.)
Thanks, Dave, for actually explaining the concepts and increasing my understanding!
Precisely. It was just Derek reminding us that he is so much more intelligent than the rest of us mere mortals.
I remember some kid played that game with me in grade school, the I'm not touching you game.... I smashed that kids head through a desk. Then I said... "Oops, I win."
As Rush Limbaugh once said "Words mean things" Things are actually touching. They are fields. They touch by exchanging photons. If you,ve ever been hit with a snowball you will understand the analogy. There is no action at a distance. A theory can be based on incorrect assumptions and still make corrections as accurate as the current state of measuring devices. Epicycles was one such theory.
Yeah, it's like asking "is a human made mostly of water, vacuum, or something else?" and then mocking someone for whatever answer they pick.
"No, it's mostly water, that's the most abundant molecule in the body!"
"No, it's mostly vacuum! By volume, all atoms are over 99% vacuum!"
"No, it's mostly baryons! Over 99% of your mass is in baryons!"
I mean, he went on about how power lines work, then used an experiment that works entirely differently to get that initial spike, which would still go through even if the lightbulb and battery weren't connected. I don't know why this angers me, but I had to vent. Maybe it's because flat earth proponents use the same sort of equivocation. It's maddening.
I think Derek is trying to inspire people to learn more about stuff he has videos about. It seems to me that none of his videos are supposed to cover the video subject fully but just give a glimpse and raise additional questions.
@@MikkoRantalainen At last, someone who "gets it". Thank you! The derisive comments above are typical of a certain mindset, they can't see beyond the end of their nose. All of Derek's videos are designed to make you think, to challenge what initially seems "obvious" and to inspire people to learn more. The fact that in doing so, he angers a few narrow minded people shouldn't stop the majority of people watching and learning.
Electroboom, I'm a retired electrical engineer. I love your video. I wanted to say, importantly, the word is impedance NOT impotence!!! Yours is the third of three videos I've watched on this. First was Veritasiums, then Dave at EEVblog, then yours. Dave said that we engineers think about things differently. That we have tools to analyze things and validly track physics and the rules of science. You fellows have collectively reminded me of much of the complexity we were trained to understand and analyze and calculate. I've much forgotten what I was trained and educated to deal with. I've been so browbeaten by the mindless politics and public chaos of people and the media news etc. I've forgotten the promises of my youth and education. RUclips, multimedia and Internet is a terrible way to waste a capable mind. You've helped to retrieve my past capabilities. Thank you. Amind is a terrible thing to waste, and you've given me a wake-up call.
Wrong place bud 😅
A more interesting question might be ”how much time does it take to switch off the light” with a massive transmission line & a resistive load (probably arbitrary & unmatched)? With all that capacitance & an unmatched resistive load, it could take longer to turn off. Same issue as the first undersea cables encountered. It distorts the sharp rising & falling edges of the signal.
well, those cheap chinese led bulbs are the answer I guess. :P
And how long does the light in the question glow with the small current if the wires are open at the end? Is it a flash of next to 0 time? Is it a flash 1m/c in duration? Does it stay on until the light speed feelers reach out to the ends of the wires to discover its open? Does it stay on forever because the bulb is infinitely sensitive and the fields will never completely stop?
I had another thought. The circuit should have a time constant if it’s a capacitive & resistive line. The time is t=RC (in its most simple form) but didn’t Derick say the resistance was assumed to be zero?! If that’s the case, by his own constraints, the t should be t=0 x C. Anything multiplied by zero is zero so the answer should be d because the resistance of the wires is zero so t also = zero not 1m/c m/s. Just a diverse thought :) ;).
The thing is, the distance does matter for the interpretation of your simulation. The capacitance of two wires 1m apart is more in the range of 10^-15 F. That leads to a much shorter voltage peak. The energy transferred in a peak that short is not enough to "switch the light bulb on" in any conventional meaning.
theoretically, the voltage peak would be the same height, voltage can't change across any capacitor instantaneously. if dave used more accurate & smaller values for the capacitance, the transient spike would decrease faster, but he specified that he didn't care about that for this simulation
Ehh... for an incandescent bulb, sure. But if it's an LED bulb, you'll at least get a few photons at the LED's design wavelength out!
@@MikeU128 hence "in any conventional meaning". You can't see a few photons.
@@stulora3172 The thought experiment is not about generating light in a bulb or LED but about the moment current starts flowing in the resistance of the load no matter how small it is.
@@ZeroInDaHouse Yes. Don't get me wrong, the simulation was very helpful and overall, Dave's approach helped me understand what happens better. No criticism. I just wanted to do the next step by evaluating what this means for the actual thought experiment. And as we are talking about "switching on" the light bulb, I wanted to point out that we would not get any perceivable light from this path of energy transfer.
Whilst we all treat ac and dc circuits differently for practical reasons, everything that applies to ac circuits must apply to steady state circuits otherwise our understanding of physics is shaky. Essentially a steady state circuit is just one with an infinitely long wavelength (relative to the length of the circuit), so all the relevant terms drop to (near) zero and can be ignored. When Derek started talking about undersea cables, I instantly thought "yeah, because it's now a transmission line where the length of the cable is relevant given the frequencies you are sending along it". But his video wasn't aimed at engineers - and like you said, if it sparks an interest in science/engineering, that's great news!
It might be well known to you and any electric engineer, but to us ordinary people, it is new and really interesting!
Pure sophisme
The simplistic visualization that I've come to love is the one of the Newton's Cradle. Imagine electrons in a circuit as being like the beads in a Newton's Cradle. The beads/electrons themselves aren't energy; they're just transferring it between each other eerily efficiently. And through this same visualization you can also begin to imagine how there can be factors that affect that efficiency.
That visualisation is no more correct than the naive "electrons are like water" interpretation though. The electrons themselves never carry energy. The power also doesn't come from them pushing on each other. The electrons are simply worked by the electric field, are induced to propagate changes in the electric field into the magnetic field, and by doing so create a favourable combined electromagnetic field that power can flow through.
They never carry energy or power, they are little links in a chainmail of energy transfer.
@@Gyzome I have always been taught that electrons are the cause of the magnetic field. If they didn't exist, then we couldn't use wires to generate the magnetic field that powers electronics if this is true.
It is very possible that the courses in electronics just don't provide the physics behind this, though it really seems that electricity needs electrons and magnetic forces to exist.
It is hard for me to reconcile the reality that larger diameter wire is capable of carrying more current if electron movement plays no role in carrying electricity.
I have always been taught that moving electrons will generate a magnetic waveform, and that a magnetic waveform will always move electrons (mostly this is from antenna theory). The implication to me seems to be the two are tied so closely together that it is effectively the same thing.
Maybe the issue I have understanding this is that a pure physics point of view, classifies energy using specific definitions that are outside the requirements of antenna theory.
My thoughts on the 1/c answer is that the battery side of the rectangle is acting like an antenna to broadcast an EM wave, and the light bulb side is acting as an antenna to relieve the EM wave. The movement of electrons sync up and move through the bulb to produce the output.
In the point of bulb output, the output of a bulb is the result of moving electrons through the filament. If the light were an LED, then the only way to get it to Emmitt light is through the movement of electrons. While the force that is moving the electrons is magnetic, I have a hard time believing that we could have electricity without movement of electrons. This is why I think people are having a hard time with this, I know it is the cause of my confusion.
@@Gyzome Not its right. Without electrons you don't have the field. The field happens as a consequence of what the electrons are doing. Not the other way around.
As everybody who's had to fight their way through differential equations knows way too well, there is a steady state solution, and a transient solution. Neither of these is right by itself, so ignoring the DC current (the steady state solution) is a fatal flaw in Derek's explanation.
Worse than that he used Maxwell's equations rather than Quantum Electro Chromodymanics.
especially because he uses a DC power source: a battery
I'm being a bit nitpicky, but steady-state and DC are not the same. Even in oscillating systems (AC) it is relevant to consider the steady-state and transients independently, as there will be some transient behaviour observed when flipping a switch to an AC supply, that will not be seen when the system is again observed long after.
@@jonathanbuzzard6648 I agree, I was waiting on someone to bring this to the quantum level ! 😅
Wrong! Derek’s explanation is also correct for DC steady state. Energy is transmitted to the load outside the wire through the field, even in DC steady state.
I was tripped up by the lack of units on option D, too.
I am a High School Science Teacher. So, I am glad you pointed out that Veritasium failed to put the Unit "Meters" after the 1 in 'Answer D'. Their original 'Answer D' was "1/c s". I am always telling Students: "Write Your Units! [or it's just wrong]". However, what you did not point out, is that having the "seconds" there in the answer is also incorrect. Since the Units of "c" [Speed of Light in a Vacuum] are already "m/s", when you divide your 1m by it, you get an answer already in Seconds. Then if you multiply that by Seconds again, you get an answer in "Seconds Squared". So actually, "D" becomes the worst answer, because of its incorrect units. And without putting in the meters, like they actually did in their video, it would be even worse... "Seconds Squared per Meter". Even if the other answers are not quantitatively correct, they are "better" because they at least have the units of "Seconds".
I'm a self learning PCB design engineer, haven't got around transmission line theory yet, vertiasium's video really confused the crap out of me, this video makes a whole lot more sense.
Look up and go watch some vids on transmission line theory. V's video was at best disingenuous for all the reasons that EEV talks about here. Take them slowly at first because you'll be dealing with everything E&M. But TL theory is the ultimate expression of EM theory and it rocks. And you don't have to understand the maths, just accept them as presented. TL theory is also the basis of waveguide operation, and both are essential at the high frequencies used these days on PCBs. Best wishes!
The video triggered me. I was like yes…what he says is true, but there is a trick here. Oh it’s a transmission line 300 million meters across and only one meter long. The old physics trick of assuming ideal conditions, and drawing the problem differently to throw us regular folks off. Thanks for the explanation, I needed the refresher…have not done drift velocity since 2nd year, and attempted maxwell equations since 3rd and 4th year of engineering school. Great video for us out of practice EEs
I am wondering thought, what does ideal conditions imply? Does it imply that the impedance is zero? Wouldn't that also mean that the capacitance and inductance of the wire must be zero?
Derek claimed that the light would come on after just nanoseconds. That means the length of the wires past the first few metres is irrelevant due to causality. So if he is correct, he is talking about a transmission line a few metres across and one metre long. Certainly not enough to turn on any bulb I'm aware of. And he directly implied in the video that this was directly testable with actual "power lines".
@@goodwillhart He did mention it is hypothetical unrealistic lamp that turn on right away.
I’ve never been convinced that Veritassium quite knows what he’s talking about. You explained it WAY better than he did. He just did not convey the thought as well as you did. Veritassium seems to sensationalize things, I think. I sometimes wonder if he understands as much of the subject as he thinks he does. Good work, Dave.
Derek basically did a video showing that if you don't 'sensationalize' your video somehow, it won't get clicks.
Yea I think he's more concerned with generating more comments and views than with explaining the concepts clearly and concisely. Which is too bad because I really believe Derek started his channel with the intent to help people learn, but now it's become all about pleasing the algorithm.
@@onjofilms well that kind of sensationalism surely works for easier to impress teens and novice adults but to me it's been a while since I've watched on of his videos just because it's more edutainment than properly educational.
a related video on veritasium ruclips.net/video/CM0aohBfUTc/видео.html
Ah, but you must keep in mind the over-riding objective: to get clicks and views so you can enjoy that "sweet youtube money." (Quote from ElectroBoom, the all-time champion of sensationalism, and who, incidentally, is also an electrical engineer.) Give credit where credit is due!
Saying “correct” is a little up one’s self.
Saying “I agree” places your knowledge and experiences in science ( challengeable)
I enjoy your channel and knowledge sharing, thx for the efforts.
As a total uneducated person, I appreciate your explanations.
Some of them really help me understand topics, while quite a few opened my eyes already.
Thank you for your understanding, which leads to our understanding, thank you a lot!
Electricity is really simple to pick up but bloody hard to master. You start of with comparing everything to water pipes. Valves are switches, water pressure is voltage and the volume equals current. And that simple comparison works for almost everything an electrician needs to know. The biggest difference between the run of the mill electrician and the layman is that the former is supposed to follow code. It only gets interesting once you go either really small or really large. When frequency and distance becomes an issue or electromagnetic fields get powerful enough to warp your conduits. That's were the fun stuff starts.
Agreed that EEs are taught about drift velocity but I remember this was in an 2nd year intro to device physics class which some EE's do not take.
Consider that many EE don't even learn the basics of transmission lines (my own undergrad experience).
The Poynting vector stuff was definitely not taught to most EE because that would probably be 3rd year advanced E&M and on the physics side of EE.
For me E&M was mandatory 3rd year. Every EE student at my university had to take it, and a lot of them failed because it was really hard. I still remember one of the questions on the midterm was just "Derive the Poynting vector." I studied my ass off and still got a C in that class.
Poynting vectors are definitely taught in EE undergraduate curricula. I think third year would be typical.
@@rsm3t -- It depends on your definition of the word "taught". I taught my pet goldfish calculus. He really couldn't sit still, but I'm sure he was a good listener.
@@poopytowncat Absolutely irrelevant to anything here, but you do you.
@@rsm3t -- "Absolutely irrelevant to anything here, but you do you." Perhaps more punctuation would make your sentence make more sense.
After watching Dave's video I now understand Veritasium's video...great explanation Dave...glad you covered this...
So, the energy will reach the bulb through 1 meter of space, by the means of capacitive coupling, way before the far ends of the wires start conducting?
Correct. You can also model it as an electromagnetic wave over the same distance if you prefer. I just like the capacitor model.
The question is just how much energy. That really depends but it will not be a lot. Probably in the low single digits percentages.
@@nukularpictures Depends on your transmission line impedance. Or the easiest explanation: The closer the wire, the bigger the capacitance and the smaller the inductance so more power on the first transient. And by "the closer the wire" I mean that you keep the light bulb and battery 1m apart but just move the wires so they kinda look like an L shape.
For the first 1/2 second, the result must be the same as though the circuit was broken at the far ends, because there's no way for the Derek/switch/load system to know whether those wires are actually connected.
@@allesklarklaus147 shouldn't it also depend on the Switching Speed? A simple Click-Clack Katschunk switch should have enough contact resistance for a 12V Battery to have a smooth enough turn on ramp that you won't see anything at 1m distance. Not even thinking about the horrible response time of a lead-acid battery in high frequency application.
"Every engineer is taught this!" .. Yes, we are. This video is pointed at those who didn't go into engineering and only have high school understanding of how it works.
Which you said. So repeating it over and over doesn't help.
Not to mention I may have been taught it, but it sure doesn't mean I remember it, lol. Feels a little degrading to be repeatedly told "every electrical engineer knows this!" I didn't know/remember it, so I guess I'm not an EE. :( Should I tell my boss or have Dave do it?
Those who look for offense, will find it.
Nice overview, with a few "footnotes":
- "signal" and "power" transmission is no different. Even in a telegraph system, the S/N ratio is calculated by accounting for the "signal power" (meaning, there is no signal without power). Of course, some concessions may be made at 50Hz, as opposed to 2.4GHz; nevertheless, when crossing the Atlantic, even for 50Hz, the characteristic impedance of the cable plays a big role, and cannot be ignored.
- the CircuitLab sim does not account for inductive coupling between L7:L8-like pairs.
I had called-out the "dimension mismatch" on Derek's vid, btw :) Nevertheless, I think Dave overestimates "most engineers" :p
from what i understand there is a significant difference between signal and power transmission(even ac power transmission) as with power you will just have phase shift and power loss. but the signal will be completely distorted due to the different frequencies it contains(square wave). and when looking at dc power transmission it's completely different(but I don't think anybody would want to do power transmission over such a telegraph cable)
@@clemenswalter1984 Yeap there is a difference in the 50ohm and 75ohm cables, were 50ohm cables transfers more power, and 75ohm more voltage. Meaning one cable transmit and one for receiving.
@@clemenswalter1984 Distortion is a thing in power systems too though, for example higher frequencies different from the desired fundamental one.
32:00 "that capacitance at time 0 is a short circuit"
that was genius, this really drove the point home for me! finally i could understand this properly! if you analyze the problem very slowly at steps of nanoseconds this makes so much sense! thank you!!!!!
It is short because at t=0 you have a "infinite" derivative (a dirac delta) on the voltage between the capacitor terminals and therefore its admittance for that infinitesimal instance t=0 will be infinite. In simulation you see this effect discretized to the minimum time step that is 1us.
As a physicist, it's interesting the difference in how we care about the fundamental concepts while engineers only care about whether its practical or not. Lots of stuff are totally unimportant when it comes to building practical things, but are conceptually interesting and important to understand. I haven't had time to see the Veritasium video in detail yet. But generally his videos are not about practical engineering or trying to teach engineers something new they didn't know about. It's more about teaching the general public about interesting and sometimes fundamental concepts in how physics work. Sometimes these interesting effects have no important practical effect in the context discussed, yet those familiar contexts are often a good place to gain understanding about them.
(I have only skimmed these two videos, so excuse my ignorance if I've misunderstood something. I just found it interesting, from a physicists pov, that at the end of the EEVblog video above, I felt Dave was essentially saying that concepts that do not practical engineering value aren't worth mentioning. Which I totally get from an engineering perspective, but as a physicist we rather love these subtle unintuitive effects that are easy to miss since they have little practical value.)
I think you'll that with many fields in science/engineering. Many physicists don't really care about concepts in pure mathematics either (and misuses them... but hey it works :shrugs: )
@@Carnassial0915 That's definitely true about physics and math. To the annoyance of mathematicians.
Exactly. I find it irksome that this gentleman is harping on the fact Veritasium's video is not new science. Who ever thought it was? It's an explanation of known physics aimed at a general audience, and a rather enlightening one at that.
THANK YOU SO MUCH! I found his video on one side extremely detailed, and on the other side just ending in a dull statement without any real life explanation which effect causes "energy transmission" over the short distance. It starts with physics end ends with mysticism. Thank you so much for this video!
Physicists love spending time on debating the "correctness" of different interpretations that lead to the exact same end result. The current flows as a result of the fields and the fields induce the currents in the conductor. They are not mutually exclusive concepts, in fact, they are coupled and cannot be analyzed independently, therefore being both essential parts of the description of electromagnetism.
In addition, that circuit can, in fact, be described in terms of more conventional circuit theory, but the effects of propagation would be modeled by discrete components (inductors, capacitors) or, in a more complex approach, with a transmission line. Those models won't tell you the value of the current in every single point of the wire and, consequently, nor will they give you the value of the fields around them, but they can model the value of the current in the wires over time at some points of the wire (e.g. near the source and near the load).
"The current flows as a result of the fields and the fields induce the currents in the conductor. They are not mutually exclusive concepts"
@@interestedparty00 Yeah, it's basically a transformer until the circuit "knows" it's been completed, as far as I can tell
You'd get the same effect if the wires were infinitely long and disconnected from each other
They do and they also care about using the correct units. The answer is E and m^-1s^2 is not a measure of time.
@@interestedparty00 Couldn't agree more, completely misleading and confusing. The problem can be solved with the most basic laws of electromagnetism, but he makes it sound like some unknown physics concept that has many practical implications.
@@interestedparty00 you still don't get it, you need to rewatch veritasium's video and EEVblog , they both teach that , contrary to what you claim, most of the energy is traveling outside of the wires
My biggest issue with Derek's illustration is that he ignores the density of the fields. All his pointing vectors are the same magnitude and therefore the viewer is led to believe that the energy flowing through the air is just as big a contributor as around the wires. In reality, voltage applied to a wire induces an electrical pressure wave (E field) to the electronics spreading out at essentially the speed of light. As each electron reacts to this pressure wave, they are pushed or pulled. As each electron is accelerated, it induces what we refer to as a magnetic field, which is a model that shows the effect that the movement of that electron has on all the surrounding electrons. What frustrates me about Derek's explanation is that he seems to imply that the wire is inconsequential. This is absolutely not true as the wire houses all the electrons in a very mobile state that allows the E field to get them moving to allow the creation of a B field. In addition, field theory shows that the density of the B field is highest right at the electron moving and drops very quickly as you move away, therefore the pointing vectors should be very "thick" right on the wires and get much much less consequential as you move away from the wires. As Derek setup the problem, he is correct, the light will flicker 1/C s after you close the switch, but only due to the capacitive and then inductive coupling of the wires, full power will take much, much, much, much longer due to the transmission line Dave discusses taking a very long time to settle out.
Exactly. On one side, Derek was talking about magnetic field around the wire responsible for transmission of energy, and at the same time he was forgetting who is creating that magnetic field in the first place. As the Dave said, it is disingenuous to miss these details.
And he's a maudlin schlub.
When you say inductive and capacitive coupling of the wires, are you saying that one wire is a transmitting antenna and the other a receiving antenna? Because if that is the case then Derek's video seems like a pedantic waste of time and he seems like a snob since as this video points out, everyone who (needs to) know(s) about wires radiating EM waves already knows that the amount of energy transfer across the 1m space is not the full energy and might not even be enough to actually power the bulb. Also, the simplifying assumptions are ridiculous and do not match the conditions under which he turned on a real light.
This & Mandeep's comment get it right. The way he talks about power transmission (in real life) in the same video, implies the energy is carried by that electromagnetic field *between* the wires. In reality, it is carried by the electromagnetic field along the wire -- not over the air directly to the lamp.
In his example, the circuits with the switch and with the lamp would not need to be connected to get to the same result he did; that is, if you only care about the energy carried over between the wires through the air in 1 m/c.
@@sakaricajanus90 Very true. You have rightly pointed out & clarify the part which can otherwise create confusion in non-technical people.
"The light bulb has to turn on immediately current passes through it"
"That's fine"
No, it isn't fine. If you do the calculations, even roughly, there is less power going into the light bulb due to the antenna effect than a moth's fart. It definitely will not light up the bulb.
iirc the lightbulb is specified to light up at the tiniest current. If you don't like that, ramp up the voltage to some ridiculous number instead.
I totally agree with you that the induced flow of energy "due to antenna effect" in Veritasium's set up is so tiny due to the low voltage of the battery that it is not going to light up the light bulb shown in his video. However, if the wire is assumed to have zero electrical resistance, the light bulb would light up due to flow of electrons inside the filament (no matter how slow they flow) pumped by the battery but not due to tiny flow of electrons due to antenna effect. Besides, the battery provides DC. For the antenna effect to work continuously, the power source needs to be AC. Veritasium is not very smart to accuse people of lying when they say the light bulb lights up because of the flow of electrons when that is in fact the case.
It sounds like you're missing the actual point
@@chaklee435 Is it an "ideal" wire with no RLC - or are real world LC applicable? 300,000 km of wire with resultant massive inductance? Good luck when you open the contacts (back EMF)!
@@simon6071 Alright I'm bored, let's dissect your comment.
1.) of course the setup would not light up any real lightbulb. That's not the point. It's a physics thought experiment, not an exercise in engineering. Any current will do.
If you'd prefer, we can contrive a lightbulb that works to our specifications. We can arbitrarily define how much visible light is required to consider the lightbulb lit. Then we grab an incandescent and heat it up in an oven until we are exactly on the line of not being lit. Then any current will tip us over the line.
2.) How is it that you are able to imagine millions of miles of wire with no impedance, but not a lightbulb that lights at any non-zero current?
3.) Why do we care that whether the antenna effect works continuously? The question is when the bulb is lit, not when the bulb is lit continuously for some amount of time.
4.) I'm no electrical engineer, but it seems that the fields are able to explain more phenomena than electron flow. That's makes fields technically correct, the best kind of correct ;). It's not lying to correct people on mostly useless technical points.
5.) The point of the whole thought experiment is to engage your intuition, and show that it is incomplete. I presume you have watched at least 2 videos on this topic, and still decided that your intuition was right the first time. Please don't get into politics, thanks.
@10:30 "a piece of restive wire" and "the battery" are mixed up. Even with DC the poynting vector always points out of the battery, because the E-field around the battery is reversed compared the the E-field around a resistance, whereas the direction of current ist the same in both cases.
Love how you did a "I'm not worthy" when Derek introduces Maxwell. That guy was the real deal. And then, you did it again for Poynting who should really be in the popular pantheon but for some reason isn't. But I do have to add Dave that Derek's video is most certainly not aimed at 'Geers and hopefully no physicist "learned" anything from it except maybe how better to explain it!
You rock at explaining the stuff. As electric engineering student, I very appreciate your explanations. Very on point
If the energy flows in a field surrounding the copper atoms that make up the wire, then the wire must act as an inside-out conduit or guiding line. Energy can flow without wire (radio waves etc.) but the wire (conductor) acts as a facilitator or focusing agent. This brings to mind some questions about the physical aspects of the wire. If you compare the electrical qualities of a Kilo of copper in the form of an ingot or a pile of copper pennies or a line of copper wire or any other form you may imagine each different physical embodiment of one kilo of copper will have unique electrical qualities. This makes me think that wire may have been one of the world's greatest inventions.
You may not be able to touch that electron directly, but you're still moving that electron, and that moving electron is still the source of the 'energy'. Put some reversed magnets in a tube as a stand in for electrons. You can put energy in by crashing other magnet's fields into the ones in the tube. The momentum energy is IN THE MASS and momentum of the magnet, even though the way you get it there is indirectly through the field. The energy goes through the field and into the magnet, and comes back out through the field interactions. At no point is the energy just 'sitting' in the field somehow, that is merely the mechanism of interaction to get it into and out of the magnet.
You may get the energy into the electrons by way of their field and be able to do that both inside and slightly outside of the conductor, but the energy is very much in the momentum and voltage levels of the electrons. Those fields don't move themselves, they aren't an independent energy holder from the electrons.
Realize for electrons in a conductor the real 'energy' is in lifting the electron sea away from their preferred ground state. If you have trillions of electrons on a conductor, and add a billion you've raised the state of all the electrons. That's why you can connect a path anywhere along the conductor and the electrons will deliver energy into the load. While you can get energy in and out by way of the field, at no point is the energy stored 'in' the field, it's sourced and sinked into that electron sea energy level.
'Energy can flow without wire (radio waves etc.) but the wire (conductor) acts as a facilitator or focusing agent.'
Realize when you do this, you've done specific things to 'use' the energy in the wire to 'make' the radio energy. You've done a conversion process, it's not the 'same energy' just moved off the wire. In a way it is the same energy, in a way you've used one form and generated another.
If you use muscle power to raise water to the top of a hill, are you thinking of that potential energy stored in the raised water as the same 'muscle energy' that was in your arm? Similarly in a way it is, in a way it isn't.
But in both cases, it's not really just 'directly the energy you originally had' moved to a different place, there's a very specific conversion process required, not just 'energy went from here to there'..
And insulation with low K the jam to that toast.
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All about induction transmission
Watching this video and hearing "This is nothing new for engineers" leaves me disappointed with the professors that we had way back at the university.
These concepts was not discussed in this captivating manner. In opens up another view to see the world of circuits. I commend the comprehensiveness of your understanding on this topic.
It's like I found a missing piece on a jigsaw puzzle.
Oh snap... I wish everyone had the professors I had, this was 1st year stuff...
Field theory is the source of circuit theory.
Between Derrick's original video and this one, I really understand this so much better. Thanks for making this interesting.
I totally agree. :)