Can The Faraday Paradox Be Solved?
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- Опубликовано: 28 фев 2024
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Here is a good paper about the paradox and additional experiments where they spin the closing circuit as well. www.nature.com/articles/s4159... 
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what happens when magnet rotates opposite direction, does voltage increase?
Anyone remember when we used to have to pause the cd player to roll the passenger window down cuz we didnt want anyone to miss the lyrics.
It's got electrolytes!
Did you really have the same idea as me recently. Which kind of tells me there is a zeitgeist that is communicating with our subconscious. I think that's why a lot of inventions or discoveries are invented or discovered at the same time.!
I should note that Faraday's disk itself is an exception to Faraday's law. When the disc rotates there is an emf from v×B, but with no change in the linked flux.There are a few others as well, like when two metal plates with slightly curved edges are rocked in a uniform magnetic field, there can be a large change in the flux linkage without the generation of an emf. Also, another interesting point. Notice how when I moved the whole contraption with the multimeter and the red wire on the magnet, there was no induced voltage. That is because everything is moving, even the measurement reference frame. If I only moved the red wire and the magnet together but left the other wires on the table then I would still get a voltage. That means that when I set the magnet on the moving disk, if the measurement device were rotating with the disk then there would be no voltage induced. Here is a great paper that actually tests out spinning the closing circuit. www.nature.com/articles/s41598-022-21155-x. And a lot of people are getting upset about magnetic field lines in the comments. I didn't make up the concept of magnetic field lines, nor Faraday's paradox. This concept and Faraday's paradox have been discussed for over 200 years, lol.
My Problem with this paradox comes with the fact that if you would have a very long, thin but conductive, axis on which to spin the disc&magnet system on and take the measure from the far end of the axis, far away and thus shielded from the rotating magnet, one would still measure the Voltage, wouldn't you?
Change the orientation of the wires to perpendicular to the rotating disk.
maybe it's got something to do with a magnetic field oscillating
1:35 An alternative set up to that image is in my head with this 3:51 principle, and I don't know how to explain it :'(
just do one more experiment for me with this setup. you have your 2 probes, one on the disk, one on its shaft allright ? now, rotate the magnet over the disk, you supposedly do not get any voltage reading. now, rotate the contact probes too. while you rotate the magnet. and you will highly likely see a voltage. disk it self stays stationary.
Spinning the magnet and the disc together still produces a voltage because OTHER parts of the circuit are stationary. There is still relative motion between the magnet and the circuit, just not between the magnet and the disc specifically. If you put the entire apparatus on a turntable, then you will get no voltage, as expected.
As for why the spinning magnet doesn't produce a voltage, actually it does -- but it produces the SAME voltage on both sides of the circuit. If you connected two multimeters to the circuit, one on each side, with a ground connection in the middle, you would see identical voltage readouts on both multimeters.
I hadn't figured out the second part yet,.. and it still might take a second for the understanding to soak in,.. but yes the first part is exactly what I was going to say,.. if he can remember when he drew a dotted line explaining that the circuit went up one brush across the radius of the disc contacting the second brush,.. The circuit will stay in that radius between the two brushes regardless of the position of the disc,.. which I do believe was the entire purpose of using a disc,..
what if we dont spin anything but merely connect 100 wires around the perimeter and switch them electronically to a single wire one after the other?
exactly
I don't get it. Why when magnet and the disc spinning together it's not "it produces the SAME voltage on both sides of the circuit"? As I understand only difference is speed of the disc and circuit is exactly same.
@@user-oe9cw3fj8h the disc works as a moving wire between the contacts, other parts of the disc do nothing.
Here's the next experiment you need to do: The same spinning disk but your closing wires run parallel to the magnetic field (i.e. Straight up and down), so they don't cut through the field lines.
I think the description that magnetic field lines is just a construct make the most sense to me. An electromagnetic field is literally just described with the polarity and strength of a section of the field, and any "lines" just outline areas where the strength is the same, kind of like a pressure or temperature map.
This makes a lot of sense. Do I understand you to mean that it is like thinking that a topographical map indicates actual lines on the earth rather than a continuously changing elevation?
yeah, the magnets are just concentrating what is already there, so of course when you spin one, it has no effect. (my guess)
Not sure if when general relativity is accounted for if the field lines rotate with the dragging of the frame.
i mean yeah, that is literally the definition of "field" (in the physics sense).
Yup, when you think about what "lines" actually are, usually it's iron filings (which basically become small temporary bar magnets, of course they're going to make lines) or similar small ferrous substance that'll do the same. Sure you might get field lines that are in consistent places but that's likely due to the size of the iron filings.
It's the same with electric fields, something moves because the electric field preferentially goes through it, of course similar substances will go to where the field gets concentrated (which is through the substance that's being affected by the electric field, so you get lines).
"Field lines" are just a by product of the testing method, which happen to be useful to describe the field.
Now gravity though, that doesn't have field lines but it's still a field
Your disc magnet has north / south poles on it's faces, and the field lines are concentrated around the edge by the steel cup it's mounted in. When the aluminum disc is rotating under it. it's cutting through the field as it passes by the edge of the magnet. When the magnet is rotating, the edge field is equal all around, so it's not cutting through the conductor, and not generating voltage. If you had a magnet disc with north and south poles alternating around one face, it would work.
That is my thinking as well. A disk magnet with a single pole facing the aluminum disk can spin but will not produce magnetic field changes UNLESS the magnet is not completely uniform and/or not spinning exactly centered. in the case of spinning a magnet over the meter probes, they were about 90 degrees out of spin phase and a better display instrument would be an oscilloscope showing an alternating current as the strongest part of the magnetic field passed over one probe then over the other probe.
Without knowing precisely the magnetic forces on that refrigerator magnet one must guess at what is happening and why.
The Faraday generator still works even if the magnetic field is symmetric around the axis of rotation.
Exactly, I believe the same
Finally, the right answer.
not sure what u mean by work. u would get AC output in that case, not DC
The shot you use that shows the scientists talking about something was very helpful to illustrate the concept of scientists discussing science.
Only 60 seconds in and already understand how generators/motors work. 🎉 Phenomenal
REALLY Really need more such videos, As a high school student, it's fascinating for me because I Have learnt about these topics in school and now I'm applying these concepts in this paradoxes which is very cool
Yes me too I studied while prep for jee
*Dr Stone fans already knowing this information:* 🤓
I remember him building one with two big copper discs
Most shows I skip to the fights. With dr stone I only skip the fights. lol
Yep 👍
It's amazing how much the anime got right and wrong at the same time but it made it extremely entertaining the way they played out the story
Yeah, schoolers also familiar with this phenomenon
The science guy was holding the ipad upside down at 8mins 22secs!
When magnet and wire are spinning together does the rotating magnet not induce a current across the brushes, negating the effect of the wire?
And when one is stationary, the wire will disrupt the magnetic field thereby disturbing flow across the brushes because the wire becomes a second magnet.
Just a thought!
Thanks for the vid - very interesting!
Thank you for making this video. Please make more such videos on other paradoxes in physics.
I've been watching your videos for over fives years. It's wonderful to see the production value rising recently but the style staying the same: informative and somewhat entertaining.
nice, I just got here
I think "cutting field lines" is a red herring. What induces a voltage is a change in flux through a closed circuit, whether the magnet producing that flux is rotating or not is irrelevant. Consider a single wire rotating from the axis. As it rotates past the brushes the enclosed area changes, and flux being field * area this results in the induced voltage. But this requires a finite width brush. In the limit of infinite wires and an infinitely thin brush you will still get a voltage but generate no current. To generate current you require a finite width brush.
If that were true, doubling the width of the brushes should give twice the voltage from the rotating disk, because it doubles the change in area. But that's not what happens.
@@gcewingNo it doesn't. The loop is the disk *and* the wires. The induced EMF here is from the Hall effect. Ordinarily, induced EMF is produced by a changing magnetic field producing a nonconservative electric field. When the wire is moved instead, the actual driver is the Lorentz force, not a nonconservative electric field
I wonder if you can recreate this by taking a magnet to the north or south pool to use the earth's magnetic field as part of the circuit. Infinite energy perhaps?
@@fabledarchon176Why would you need to take a magnet to the north or south pole if you’re going to the north or south pole?
This should, however, imply that with the correct ways to amplify the signal, we can generate electricity from our own bodies. In fact, even if we didn’t generate usable energy, it’s entirely possible that this principle is the reason any electrical signals can propagate through our or any other organism’s bodies at all.
∇⃗ ⨯ E⃗ = -∂B⃗/∂t
thats, whats going on, not the explanation in the video. There ist a magnetic field B⃗ (flux density) in up-down-direction. If the density of this field varies, an electric field is generated clockwise, or counterclockwise rotating. Due to the material Al, this electric field generates a current in the same, rotating direction:
j⃗ = σ E⃗
This current generates an magnetic field, that is directed in the opposit direction to the change in B⃗ it results from
∇⃗ ⨯ H⃗ = j⃗ + ∂D⃗/∂t (with D⃗=0)
B⃗ = μ H⃗
so as a result, we are not talking about induction, not about faraday's law, but instead about the full set of maxwell equations. Because it's not the magnetic field of the magnet that generates the effect, but a secondary magnetic field, produced by the magnet a first magnetic field. While the first magnetic field ist independent from radius, the second one is not (eddy current). And that's what can be measured.
there's no paradox (as readily described in the *first sentence* of the wikipedia article even), your model of allegedly actually existing fieldlines is simply "too coarse". in the case of the spinning disk, you're spinning the electrons rapidly through a magnetic field, while in the case of the spinning magnet you're spinning a magnet that still produces a uniform field. so in the first case the individual electrons experience a locally changing magnetic field, by being physically pushed into/out of it *and* into/out of the wires/brushes. which also therefore explains your 3rd case of "both moving together": think van-der-graaf generator but made out of "electrons stuck in magnetic field" instead of "stuck as charge on insulating surface". because if the electrons wanted to avoid going along your "loop" bit of the plate, they'd have to move relative to the magnetic field, which as we know requires additional energy. so the lower energy solution is to simply flow through your circuit. there's no such thing as a "moving field", there's just a "moving area in the universal field of magnetic force that we currently claim kinda belongs to this magnet somehow". there's only change in magnetic flux (and of course electric potentials, like that nice low-resistance path through your brushes) to the individual electron.
and your "one other point" is plainly wrong, if you spin a bar magnet you very much induce a current, that's literally the whole point of eddys.
That's why I said there is not paradox in the video. Also the concept of field lines is not "my model", lol. Also for the bar magnet it doesn't induce a current in this setup because the same amount of magnetic flux is always in the loop. You should try it and see for yourself. Spin a bar magnet over a portion of a closed loop (north or south pole facing down over the wire) of wire so that the same pole is always facing towards the wire and there is not current induced.
ah hiding dissenting *facts*, i see.
The way i think of this is regarding the fact that this specific magnet has a rotating symmetry, if you rotate it, the magnetic field wouldn't change. The voltage is generated by a relative motion between the field and the wire, not the magnet itself and the wire. Its not that the magnetic field is stationary, its that rotating it doesnt change it. To change the magnetic field you need to either translate it relative to the wire disc, or rotate it into a non symetric axis. I think this confusion is made because of how people usualy describe the magnetic field visually, with single lines going from the center around the object, giving the impression that rotating the object also rotate those "lines", but the fact is that the magnetic field is homogenous around an specific radius distance ring, it doesnt have any "lines", nor any phisical phenomena that "rotates" with it, because magnetic field is an interaction force, and not a physical object
The plane of rotation is orthogonal to the field. When the metal is rotating, it is moving at right angles to the field, whether the magnet rotates of not.
The experiment has violated Faraday's law, but it has not violated Lorentz's theorem.
It's neat that the part where you move a wire over the magnet to create charge is basically how electric guitar pickups work. Never thought of it at a larger scale for some reason.
Its how car alternators work also. Just stronger magnets, and a lot more wire
I tried this in college with two toroidal magnets out of speakers (same as you had with your drill) but I machined a brass disk mounted to a brass axle such that the two toroidal magnets were placed on either side of the disk and because the disk was only about an eighth of an inch thick, the natural magnetic attraction of the two magnets clamped and rotated with the disk. I then put a multimeter from a brush on the outside edge of the disk and the axle and noted that in either case (whether magnet was held stationary or allowed to spin with the disk) a voltage was developed. I asked my physics professor and we never figured out what was going on. He referenced a very old book where the author claimed that the resolution lie in something to do with relativity (not around during Faraday). But I honestly never understood it sufficiently. I do remember the author claiming that if two equally charged particles a distance x apart were stationary then the force of repulsion was purely electrostatic. But if you as the observer were moving relative to the two particles, then the observed force between them was then a combination of electrostatic and magnetic because the motion gave rise to magnetic field around the charged particles.
I found your description excellent. Now subscribed.
my name is Barry McGrath of Graniteville SC. Here is your answer and my suggested "law". Bipolar magnetic feilds, like water seeking its own level, "seek" their own or regulate their own volume according to their own strength. So you see the spin of the outside object has no power of disrupting said volume shape because it is not displacing any aspect of the magnetic feild. When the magnet spins, that feild is being displaced itself through the twisting of the volume and therefore creating voltage. You are welcome. I love your videos, you are awesome.
is this a bit like the difference between rotating a cup filled with water and the water not moving vs putting a spoon in the cup?
Thank you for this. I'm a auto mechanic and I now have a better understanding on how hall effect sensors work. Keep up the awesome content I love learning!
How exactly did this help you understand how a Hall effect sensor works?
I think you have mixed up hall effect sensor with inductive sensor.
@@nowayjose596😂😂😂
another angle: the electrons try to move in a circle. See: particle beams and magnets
Very cool demonstration of an interesting effect! And as the professor said when the student complained that the result was counterintuitive, "When it comes to rotating invisible fields of force, you have no intuition"
Good one ^^
Reminds me of another one: "All models are wrong, but some are more usefull than others."
This blew my mind. I reasoned out that the full circuit mattered just about before you started explaining it. I wonder what sort of fun could one have with spinning semiconductors. A spinning silicon disk that's npn or pnp could act like a transistor that's spinning constantly. So the magnetic field is like a potential voltage when the base of the disk transistor has a voltage applied to it. I could picture a wild rube goldberg type analog/digital computer.
Maybe you get to dope the different layers in 2 dimensions now to create interesting oscillations... a NPN transistor could be swapped to a PNP one, or the values changed so that radially the transistor has different values depending on its rotation.
Interesting ideas just from your video.. I love it. Thank you for sharing!
Now I understand, thank you for the demo. The circuit drags, then jumps, then drags again.
When you spin magnet above starionary circuit nothing should happen. Magnet rotates yes but the magnet field doesnt change. So both are basicly stationary then how there should be voltage if both are stationary? ---- this happen also when magnet is attached to disc... the field is stationary but circuit under it rotates thefore there should be voltage --- nothing confusing therd.
@electroboom where you at? 👀
The hospital...
@@punknoodles0 🤣
Despite my other comment your channel is one of the best on Internet about Physics AND you gave motor and generator brushes a new literal meaning using real brushes.
And the movement of the wire across the magnet producing a charge is exactly how an electric guitar pickup works. When you pluck a metal string it moves back and forth over a copper-wound magnet which is grounded to the strings. The tiny electric charge is then amplified; the speed of the back and forth motion of the string electrically reproducing the pitch of the vibrating string.
I think you'll find that the mechanism at work is variable reluctance.; the string moving over the polepiece is altering the strength of the magnetic field impinging on the pickup coil. The strings are either steel or have a steel core and are magnetically suceptible. The strings themselves do not form a closed circuit; the tuning peg end of the strings is isolated electrically from all other parts of the guitar but even if they weren't, the magnetic variation near the pickup pole will persist.
Flying saucers are powered by the earth’s magnetic field confirmed 😊
WTF is magnetic viewing paper? Do a video on that!!
Compared to this video, that video would be 30 seconds long. Metal particles suspended in a medium inside a paper thin confinement. Magnet “viewing paper”
I have an answer now; the emf/voltage in the wire is generated by the electrons as we know. The electrons need to be moving in a magnetic field to cause them to side-deflect and the final voltage is the sum of all the deflection forces. Because of uniformity, the magnetic field of the disc is the same if it is moving or not.. this is like seeing a row of 11111 moving along and noticing no change. So when the disc magnet is rotated and the conductor(electron-carrying disc) is stationary, there will be no emf- as the electrons are not moving.
When both the magnet and disc are rotating there will be emf as the electrons are moving- as they see a uniform magnetic field- whether the magnet is rotating or not.
So if we now rotate the emf sensor with the rotating metal disc(as in my last month's comment) there will be an emf according to the above. The wires of the external circuit being stationary or not doesn't make a difference- contrary to what has been suggested by some books.
Thank you very much.
One thing I love about this channel is how unceremoniously the videos ends.
he said "see you next time", thats a ceremony
what if the closing wires are oriented differently and come from the bottum instead of from the side for example?
Im in the "theres nothing to rotate" club
An understanding of whether the field rotates or not delves deep into the relativistic origins of magnetic fields. Relativistic field transformation makes it so either the magnetic or electric field move the charges in either frame of reference, but you can also think of it like both fields being one and the same, a single field fulfilling the laws of special relativity
Excellent video as always, and props to the Tillamook shirt!
Wow. A paradox that is resolved yet unresolved!
😂
But it ceases to be a paradox if it's resolved. The fact it's still called a paradox says it all.
@@Biggles732I guess it would be a falsidical paradox in that case. The Monty Hall paradox is an example of a falsidical one.
like the paradox of how this narrator sounds like the honey badger guy in 2024
This is one of the most genuinely scientific Action Lab videos I've ever seen. Normally they're just magic tricks that are supposed to be analogous to real concepts.
To my understanding of things... it is the path of the electrons inside the spinning disk that keep changing when the disk turn so it is considered as a moving wire compared to the magnet...
to test my theory, you need a bar of conductive material (a rule made of metal found in any good toolbox should do), 2 brushes (the ones used in this video should do) and a magnet (also, that one used in that video should do)...
place the steel rule flat on the table,
Place both brushes on the "0 in/0 mm" mark of the rule (one each side of the rule touching the rule but not touching each other)
tape the brushes in position to the table (both plugged to the multimeter as intended)
Place the magnet on top of the brushes (or near them) without it touching them
Then ... pull fast the rule without moving any other parts (make it slide in a way that the brushes will point at "12 in/300 mm")
Maby there will be a difference on how much voltage is generated... the disk have a single fix entry point for the electron and a exit that move fast but the blade have both entry and exit point moving at the same speed...
In the case when both disc and magnet rotates we can also say that due to the rotation of magnet a time varying magnetic field is produced which in turn produces an electric field which interacts with the wire beneath the disc producing current and generates voltage across wire
The magnetic field doesn't change in time (by approximation) because its rotationally symmetric. And even if it does because its not kept perfectly still the changes cause the E-field that doesn't induce a particular EMF.
It's not a paradox, rather it is a lack of understanding.
A.k.a a paradox
No a paradox is a thing that has no solution even with understanding, if it gets a solution, then it is not a paradox anymore but a problem.@@niallmcardle7
Nial, no
There is no paradox that is not just a lack of understanding
I think you lack understanding of what a paradox is
I want to see more experiments.
1) the wire at the bottom: make it perpendicular to the disk itself by extending the disk holder, thus eliminating half of the wire from equation.
2) rotate a magnet above a wire.
Think simpler than this. The Lorentz force acts orthogonally to the v x B product of the motion of a charged particle in a magnetic field. The electrons are present in the aluminum disc, and rotating the aluminum disc gives them a net velocity on the average (tangential to rotation of the disc). When you impose the magnetic field INTO the disc, you're setting up a classic situation that, locally, looks the same as a charged particle moving through a magnetic field. The Lorentz force is then radial, within the plane of the disc. This force "pushes" the electrons radially, creating a charge gradient in the disc, and thus a measurable voltage.
Rotating the magnet imparts no kinetic energy to the electrons in the disk. Rotating the disk does. So this is why the paradox evolves. It's not about relative motion between disc and physical magnet. It's about the motion of the disc itself.
The individual electron paths get tricky to work out, because there are going to be eddy effects as an actual radial electron current forms. So it's not quite so simple to work out what the output voltage is "under load" as you draw current. But the Lorentz force says this has to happen, and it does.
Have you tried spinning the magnet on the drill in reverse while the stationary disk spins in it direction? I wonder if that would generate more of a voltage because they are moving in different directions. Great content!
It seems that the magnet rotating doesn't create any voltage, so I'd assume that even if they were spinning in different directions, the voltage would stay the same, i.e. it'd be the same as in the experiment where the conductor was rotating but the magnet wasn't
This article seems super relavent to today's post and I hope you'd concider investigating/explaining the phenomenon. Please keep up the hard work.
Keep your feed wires at 90deg with the axle. This should eliminate, or close to it, any flux crossing due to the shape. You’ll need an isolated bit fr wire attached from the outer disk to the top axe brush. This wire will spin with the disk just insulated to maintain your potential differences from the inner and outer parts of the disk.
1:10 as you say here the circuit in the disk is just that one section from the middle to the edge.
this section contains electrons. these electrons need to move in relation to the magnetic field.
which they do when the disk is spinning regardless of the magnet spinning or not.
that means that the magnetic field is not changing with a perfectly round magnet.
please try it again with an asymmetric magnet to see if spinning that irregular magnetic field inducing a voltage.
also the wire/brush to the middle of the disk should be parallel to the rotational axis to isolate it from the problem.
Exactly, the magnet spinning doesn't matter as long as the magnet and its field is rotationally symmetric. The potential is caused by the free electrons moving through the wire experiencing a lorenz force causing them to move and induce a potential.
When the magnet is rotating the magnetic field is not rotating due to uniform shape and density of the magnet, it still goes from north to south of the ring that could be up to down (or vise versa) in this case. so it only induct current when disk (its atoms) are moving through this field.
But if the magnet was not uniform in shape or density or if you rotate the magnet in another axis then it inducts current.
Doesn't your magnet spin over the wire that's _under_ the disc, creating that voltage? So in other words, the disc is transferring the magnetic field through itself to that wire under it? Or would that only work if the disc were made of something with Fe in it?
I don't know if it is intentional or a coincidence, but the VW bus on your shirt is directly related to this video.
The speedometer in that bus (van, car) has a cable driven by the left front wheel, coming up to the back of the instrument panel where it turns a simple aluminum (important that it is a non-ferrous metal) circular disk. A thin air gap separates that from a circular magnet attached to a spring.
The relative angular velocity between the aluminum disk and magnetic disk through a similar mechanism related to this video's content, induces eddy currents in the aluminum disk and a resulting torque on the magnet (the speedometer side), which acts linearly against the spring which restores the speedometer needle to zero.
So there is a linear relationship between the bus velocity (left front wheel, specifically) and the angle of the speedometer needle. No electronics or wires involved. A purely mechanical system that relies on these magnetic effects. Even though I understand some physics, I was a little confused the first time I came across this in my old VW; I could not understand how the speedometer could possibly work.
yea right.. btw in order to generate electricity by messing up w the magnet, u will have to continuously change the intensity of the magnetic field..
Interesting!
I wonder what would happen if the connecting wire was just going straight down the middle so it cannot generate a voltage?
My first thought as to why the spinning magnet does not generate any voltage is that the magnetic field "lines" is just a field, without the "lines" that we use to visualize it, and therefore it's uniformly symmetric around the circle, so there's no change in magnetic field around the circle, so no voltage.
Please would you show us what happens when the wire to the centre of the disc goes straight down the rotation axis ?
It will happen the same, and you will see paradox is still unsolved!
It's wild to think about just how many devices/components rely on that principle. Speakers/microphones, motors/generators, transformers, inductors, capacitors, antennas, relays... and I'm sure there are more that I haven't thought of. All of them are based on electromagnetic induction.
4:55 this is because the electricity is moving between the two wires (left to right) in the video irrespective if the disc (bottom) is spinning or not. Right?
What we can deduce from the fact that both voltage events occur when the disc spins, is that the magnetic lines of a circular magnet don't inherently change with its spin as no polarity change occurs.
The rectangular magnet would not behave the same if spun as the polarity would move the magnetic lines.
The way to check this would be spinning the magnet in a gyroscope and seeing if tilting the magnet along its polarity would cause voltage to occur, I suspect it would.
Question. If the magnetic field lines are being cut, what if you had the magnet on the drill and rotated the plate field and magnet simultaneously at the same RPM? Thanks.
@TheActionLab, what would happen if you had a longer axel so the closing wire was outside of the magnetic field? Would it then generate voltage because the wire is not interacting with the magnetic field?
This video was very fun
Thankyou for making my day!
From what you're saying, to actually challenge this paradox. The cable touching the center of the metal plate would have to go perpendicular to it. Then the field of the magnet will not cut through it and thus create a current.
Very nicely designed experiments, to get perfect results.
So what happens if the circular magnet is bolted solidly to the spinning disc? Same result? Or is the drag from friction causing the change in magnetic field?
What if a magnet rotated with the drill and disc also rotated (with the same speed as of drill in its direction)does we can get any Volta?
Are we sure the electrons on the disk are still moving in a straight line during disc rotation? Is their movement influenced by the magnetic field and spin?
Perhaps with the magnet stationary it has time to emit its field lines, so with the disc spinning, the wire brushes and the aluminum disc catches the em field (voltage). When the magnet spins, it does not have enough time to emit its field lines (no voltage), so when they spin together they are relaying its field lines in sync (voltage).
I wonder if your metal brushes, stationary as they are, when your aluminum disk spins, are the brushes disrupting electrons in some manner so that when you drop your magnet on top the spinning disk so both spin together, the electron situation, if any would be caught in the magnets field and be the cause of the voltage readings.
Question: what happens if you make the circuit wires axisymmetric as well? I.e. you have a stationary disc and a spinning disc with ring brushes at the centre and rim.
at minute 5:25 with the 3 options (1st and last w voltage), for the 2nd option, what you have the middle axle wire/brush replaced by a perpendicular wire (a metal ball connected to the magnet ' screw and form there to voltmeter), and thus move the wire in a parallel plane w the magnetic flow, in a hope to remove the 2nd wire voltage cancellation, still you would not get a voltage of the edge brush?
Isn't the answer much simpler that you only get a current if the charges in the disc that are free to move will experience a force due to the 'stationary' magnetic field. The magnet is rotationally symmetric so there is no change in the B field in time. But the negative electrons in the conduction band of the metal experience a lorenz force when they are made to rotate through a stationary magnetic field so they experience a lateral force creating a potential across the circuit. All that matters is that the disc is rotating because that is where the free charges are that will be moved.
Surround the magnet with a mumetal shell so the field doesn't go beyond the spinning disk and see what happens. Like others have said, the magnet is inducting voltages in the wire/brushes themselves. Spinning it one top with a drill creates equal, opposing voltages on each side and thus the reading ends up at zero still (-1v + 1v = 0).
you should do the single slit experiment but using vantablack as the blocker to see if the absorption of the paint causes a different difraction pattern from the general experiment.
I did an experiment with ferrofluid as while back. I put the ferofluid over the magnet and rotated the manet. I expected to the the field lines rotate too, but they didn't.
Could you not use a wider ring magnet in the same orientation and have the lines of closure positioned vertically in the center of the axis of rotation?
cool to see the tillamook shirt, use to go every summer when going to the coast, only been there once since they sold out to a corporate company but its just how things go
The most exciting part is the advert for that product I would never buy and skipped over.
It's easy to check your hypothesis. Just connect this wire not from the side but from below. Such that magnetic lines do not cross it. And see what happens. I remember that you will still see the current (so the paradox remains).
Thanks! I have a PhD, in physics, but i did not see such a simple explanation of this experiment! Maybe if we used resistor underneath the rotating disk of the centrifuge as part of the circuit and measured the current in it by measuring the voltage drop on this resistor everything could be demonstrated more explicitly.
Can you explain a bit more about the scenario at 7:16, if the magnetic field is rotating why would induce a current in both wires including the closing wire?
The second one is easy to explain. The points at which you're attempting to pick up the current aren't changing. If they were rotating around the metal disc at the same speed as the magnet, you'd get a current.
And I agree with deusexaethrea for the last one. There are other areas of the circuit which are electrically conductive so you're introducing a moving magnetic field to them which is producing the current.
in the magnet spinning only , there is no virtual wire . the electrons are instead displaced by the magnetic field about the conducting disk as they get from the pos to the neg brush
I think it depends on the shape of the magnet.
If a bar magnet is rotating the tip of each poles definately disturb magnetic field, however if the shape is a ring then the field becomes stationary even you rotate this ring magnet.
when you place the magnet on the disk you expected no voltage... but there WAS a slight wobble because the magnet was not perfectly centered.
was that taken into consideration?
The paradox is easily resolved if you pay attention to the fact that there are electrons in the disk. When the disk rotates in a magnetic field, electrons begin to drift to the periphery according to Lorentz's law. This is how the potential difference appears, which we observe on the multimeter.
Електрони повинні дрейфувати, відносно чого? Тоді електричні контакти повинні щось тягнути за собою, створювати "вітер" в середині провідника...
I'm a little bit curious about the experimental set-up. Is the box that contains the motor/disc metallic ?
That really blagged my head when you showed 0 voltage, but then you explained it, and it made sense.
I would say that the magnetic fields exist, but when you speed the magnet up, they cancel each other out. I believe that if you run the same experiment with a much stronger and larger magenet at the same RPM, you will see a voltage.
Strong disk magnet being rotated on the axis you demonstrated surrounded by a cylindrical glass tube with another magnet being held to the side of the tube by the field of the center magnet. If the center magnet is spun, does the second magnet move around the outside of the tube? A lubricant may be required. A ring magnet surrounding the glass tube with a mark on it could also be used to test rotation. If either the standard magnet or ring magnet begin to match the rotation of the central magnet then the field is rotating.
Do you live in Oregon? Thanks for the great videos :)
Great demonstration! Should be demonstrated in the school and college!
Would be neat if that motor version of Faraday disc worked with superconductors. Superconducting junctions where contact points would be expected with a fluid bearing or air bearing and a initial current + a push. Would it keep running or would all the energy be lost to external forces.
Why not make that wire touching the center of the disc vertical and retest to solve the paradox?
The Faraday Paradox refers to a curious phenomenon in electromagnetism where Michael Faraday discovered that when a conducting loop is moved in a uniform magnetic field, there is no induced electromotive force (emf) in the loop if it is moving parallel to the magnetic field lines, despite the change in magnetic flux. However, when the loop is moved perpendicular to the magnetic field lines, an emf is induced.
This paradox can be understood by considering the forces acting on the charges in the wire. When the loop is moved parallel to the magnetic field lines, the charges experience no force due to their motion, resulting in no induced emf. However, when the loop is moved perpendicular to the magnetic field lines, the charges experience a force due to the magnetic field, resulting in an induced emf.
The resolution to the paradox lies in understanding that it's not just the motion of the loop that matters but the relative motion between the loop and the magnetic field. When the loop moves parallel to the field, there's no change in the flux through the loop, hence no induced emf. But when it moves perpendicular to the field, there's a change in flux, leading to an induced emf.
Faraday's law of electromagnetic induction explains this phenomenon mathematically, stating that the induced emf in a loop is equal to the rate of change of magnetic flux through the loop. So, there's no paradox, just a misunderstanding of the conditions required for electromagnetic induction to occur.
this problem seems to center on the magnet being a disc with axial magnetization. doesn't the flat side have a constant magnetic field relative to the disc/ wires? wouldn't this account for no induced current in the magnet spinning above the disc example?
i wonder what the result wold be spinning the flat side of a magnet with diametric magnetization?
i also noticed a wobble when the magnet was placed on the disc. would a perfectly centered magnet get the same results?
[Halfway through video:]
How is this a paradox? You have a pseudo-conductor in the disk, which is the path taken by electricity as it passes between the brushes. In an ideal homogeneous solid, this would be the shortest straight-line path through the disk between brush bristles.
When you rotate the disk but not the magnet, the flux lines from the magnet pass through a varying pseudo-conductor. The "virtual wire" is moving, because the brush contact locations are varying. So, we have flux across a varying wire and a voltage differential is observed. When the disk and magnet move together, the pseudo-conductor is still varying. So, we have flux across a varying wire and observe a voltage. However, when the magnet is rotated but *not* the disk, then the pseudo-conductor is stationary. So, we have flux across a stationary wire and observe no voltage.
I would hypothesize that the magnet is sufficiently uniform and homogeneous that the field doesn't change substantially when rotated. Flux lines are a useful construct to visualize field strength and gradient, like topo maps do for height. If the magnetic field is rotationally symmetric in intensity, or sufficiently so, then I would *expect* to observe no voltage in the moving-magnet-stationary-disk configuration. What might get interesting is if a highly non-uniform field were produced - for example, spin the two poles of a U-magnet across the face of the disk. If *that* still shows no voltage, while the flux through the pseudo-conductor is definitively varying, *then* we might have a paradox.
Edit: tldr; if the field is symmetric in the disk, then the only thing that changes in all three cases is whether you're moving the wire. If you're not, then you have neither changing field nor changing wire - and consequently no voltage. If you want to be rigorous, use a magnet with a non-symmetric field and verify with a numeric FEA software simulation that the field inside the disk is varying as you spin the magnet. If *either* the field is symmetric *or* the field spreads out in the dish and *becomes* symmetric, then no voltage should be observed.
[After finishing video:]
Yeah, field lines don't exist. If you had a perfectly symmetric homogeneous magnet, you would not be able to identify a "true" orientation from the field alone. There's nothing unique about field lines, so it's literally impossible to distinguish one from an infinitesimally-close neighbor with the same intensity. There is only ever a variation in the field intensity at a location in space. No variation, no change in flux.
Also, the closing wire hypothesis could be tested easily by using a central brush which is colinear with the disk-axis. Such a closing wire would not intersect the field lines and could therefore not contribute to the voltage differential. If the disk is sufficiently large, so that the outer brush is sufficiently far removed from the magnetic field, then its contribution would be similarly negligible.
Can we make discrete magnetic spots on a disk to do an integral or a limit equation too verify?
The field has to be stationary that's why when only the magnet rotates there is no voltage but when the disc rotates with /without the magnet the disc moves through stationary field making voltage.
The magnetic field depends on the speed of transfer. That is, the spinning of the magnet affects the field itself, which creates a type of magnetic drag, this field is likely then able to be manipulated with control of the rate of spin of the disk.
What would happen if you spin the magnet in the opposite direction of the spinning disk?
Would it produce the same current or more?
So what happens when you spin the disk magnet under that special paper you used with the bar magnet?
Is there any difference if the wires are located axially to the spinning apparatus?
Unplug cpu fans before blowing them out because they spin and may generate electricity send this back into the board. At least i always thought that.
So i unplug the cpu fan for example.
I also flip switch on the power supply and disconnect all power to the board before blowing that out.
For most fans i stop them moving with my finger when blowing dirt off components in that direction or off the fan. keep in mind im using an air compressor for roofing.