Does Kirchhoff's Law Hold? Disagreeing with a Master
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- Опубликовано: 4 ноя 2018
- This might be more of a lesson on proper probing than anything! There would be much less confusion if you have reliable results.
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Dr. Walter Lewin’s videos on Kirchhoff’s Voltage Law:
• 8.02x - Lect 16 - Elec...
• Kirchhoff's Loop Rule ...
• Believing and Science ...
• ha ha ha 5 + 3 - 8 = 0
By: Mehdi Sadaghdar
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#Kirchhoff #KVL #KCL #ElectroBOOM 
Наука
Hello team RECTIFIER! Make sure to watch the next video on the topic: ruclips.net/video/Q9LuVBfwvzA/видео.html
ElectroBOOM ok
Stop looking at the camera it feels like your looking deep into my soul.
I agree
I like how you challenge the norm, fight for the truth even if you have to oppose the majority! I hope you're indeed correct and get to have your own claim on humanity's understanding of all things electric!
HMM... there is no common earth, thus its unfair. - i bet your anomaly disappears. if you common eath the scope, too a fixed point on the input induction bolt coil.. for both tests.
You can tell he's serious because he doesn't shock himself in this video.
haha! +1
Well, I didn't understand anything but the fact that he still shocked some scientists out there
@@angelomartino4667 hehehe.
Also the altitude of his Eyebrow~s~
lol
"I couldn't be happier to be wrong and learn something new." -an important moral fiber rare these days.
So true. It's something that bothers me in almost every discussion I (try) to have with people, the rare exceptions excluded of course.
Yet it's so great to be wrong! Because now you now know better and have become a better person for it. What's not to love? :D
Yep
I literally read this the same time Mehdi said it
Are you Illuminati?
@@dimitriss.7954 I am working on it my friend.
"These days"
Nah that's a universal human bias
Bad probing is almost always the number one source of error in electronics experiments. Kudos Mehdi
My thoughts exactly! Thanks for saving me from having to comment this.
@@MikeDonaldson-eh2ru I've watched several of Lewin videos, the guy knows his stuff but often doesn't bother to explain....must be an MIT thing, gifted students expected to figure it out on their own.
If you don't understand anything, it's fine. He is not explaining it you, he is explaining it to Walter Lewin XD
This is the comment I was longing to hear....though I could grasp it up , still I didn't feel like I completely got everything he said
hahahahaha
You are just the alibi for the RUclips revenue
@@mskaroly6356 truth hurts man, but truth is truth
It's high school physics
Very well done and diplomatic ;)
And the civil engineer shows up trying to play around with the electricals.
@@Token_Nerd You shouldn't anger a civil engineer. They usually design civil structures in a way that they can hide bodies inside.
@@_aullik As a Civil Engineer, no comment >;)
And civil engineers are experts in civility!
@@89rafa Very subtle pun.
I am surprised that Dr. Lewin did not consider the mutual coupling of the coils with each other in his experiments. In his test moving the probing wires around should change his results. I could not find anything wrong with your analysis. Dr. Lewin seems to verify his hypothesis through the demonstrated experiment which appears to be flawed in how it is setup and yields an incorrect result. First step would be to correct the setup before we even discuss the issue at hand.
God has spoken.
I think this is more an EE/Physics communication barrier. The physics view is that the EMF is not strictly a property of the circuit (and which points you choose), but of the full path enclosed by the probe wires and whichever part of the circuit forms the rest of the loop. Time-varying magnetic flux changes the situation from being a conservative potential (safely path-independent) to one where the loop integral is path-dependent.
When @ElectroBOOM talks about "bad probing" or "good probing" it essentially is defined as "arranging your probes to avoid encountering the effects of flux in the path segment outside the circuit. I.e., suppressing exactly the difference Levin is talking about. When he introduces a transformer into the model, it is incorporating the probe wires into the circuit as the secondary.
The controversy is about how one classifies these issues of measuring the voltage and whether they are included in the meaning of KVL or not.
he's reading a 1 turn coild with some wires that act exactly like a 1/2 turn antiparallel coil. Of course it's gonna negate half the reading, and you dont even need to flip it. Moving the wires most change the reading because he is litteraly adding 1 and substracting 0.5
I also think this is an EE/Physics communication barrier. Faraday's Law is very clear. The voltage in a closed loop is equal to the time derivative of the magnetic flux. If there is a time varying magnetic flux present, the voltage in a closed loop is not zero and Kirchhoff's Law doesn't hold.
@@ricardonunes6724 "If there is a time varying magnetic flux present, the voltage in a closed loop is not zero and Kirchhoff's Law doesn't hold."
no, that is simply false. It holds true for dynamic systems just as well.
Teacher: The test isn't complicated
The test:
Teacher: predicts result,
Teacher: conducts experiment
Measurement: agrees with predictions
Former engineer: Nooooooo! You can't hit me!
Can i just say that watching both this and your follow up video, i think the best lesson to be learned here is how to handle a disagreement like an adult. You found someone who had reached a conclusion that you disagreed with, and were still respectful of their findings and knowledge, while showing the reasoning that lead you to disagree. If more people could handle their disputes like this the world would be a happier place. Best wishes to you.
Couldn't agree more
He did everything he could to be tactful and respectful and still got gruff. You can really tell no one has disagreed with Lewin in at least 30 years. He handled it so poorly.
@@pearz420 I kind of can see where prof. coming from. When people bother you with stupid questions and provide their demonstrations that doesn't make sense then after a while you just decide to stop going into any discussions. Maybe he had enough as educator. Of course he could have handled it better. I mean ElectroBoom certainly makes not only entertaining but also educational videos. And it would certainly benefit both of them to make a constructive argument.
"my mom thinks I'm mostly ok." 😂
r e l a t a b l e .
lol - yeah, I was glad to hear that too.
So I'm not the only one who has received that statement before 😂😂😂
the rectifierrr
Yeah my mom thinks I’m ok kinda.
Mostly lmao
"My mom thinks I'm mostly ok."
It's ok Mehdi. We're all in that boat together. Love you man. Keep up the great work!
My mom doesnt know what to do with me anymore.
My mom disowned me :c
Jk shes the best mom ever.
that ws sad
My mom does not have the same feeling about me Infact it's the complete opposite 😁
Your regular, humour-filled videos with shocking situations that make you want to go Ohm, are nice and I love them, but this video was really refreshing. Seeing you explain a confusing topic and simplifying it down so those of us, not too familiar with electronics yet can understand...dude, I need more of this. I think that is a legitimate sign of intelligence.
4:48 "I have a coil or solenoid"... Me: This is going to explode.
4:57 "The resistor limit the current to 10-12 Amps"... Me: This is going to explode.
5:30 "Now I'll measure across these two points..." Me: This time for sure.
not today my friend, not today.... he had to be serious when refuting against a distinguished professor
Whenever you see him use a capacitor and plug something into a power supply it's a done deal
That is true i though the same way 😂! I am not used to this kind of video from him !
Don't worry, the pulse is short.
And this is why science is based not on authority, but on peer review.
Or facts born out of evidence? You could argue that a bunch of professors could claim something erroneous and it would still be peer review (collective delusion or even collective error in methodology). But they cannot dispute facts.
@@youtubasoarus Be careful saying that. Anti-vaxxers and flat-earthers dispute facts all the time.
Consistently reproducible results i'd say.
"What if i test your theory this way" which is exactly what mehdi is doing and coming up with a different result. Hence, theory needs adjusting.
But then it isn't really is it? Never really has been, there's probably more politics in the scientific world than in the White House. Science is dead like in around the world in 80 days, it's all about theory and what theory is popular.
@@fordman7479 110% agree
Interesting to see you challenging Dr Lewin. Science drama is so much better than typical RUclips drama. And this is science drama _on_ RUclips! A new paradigm!
Id enjoy drama a lot more if all of it was like this!
I come to this video from time to time hoping I can understand all the concepts explained here a lot better. Out of all Mehdi's videos, this one does even more hard science than Mehdi usually does.
That being said, I have learned quite a bit from this great dude, and I do appreciate the fact that he shocks himself a lot just for the laughs and to enhance the learning experience.
One of my subscribers just turned me onto your videos. Absolutely magnificent stuff your brilliant! Going through most of your videos now it's going to take me awhile, but I'm having a blast. Thanks for sharing
Always express you thaughts. Just because he wrote 15 science books doesn't mean he Is right, or that he Is smarter than you.
Yes!
And if it is a teacher it also doesn't matter
Matija Lekovic there is no point of saying who's smarter or right, his point of view differ to that of ElectroBOOM, that's all. No matter who's correct in the end as you learn everyday, either of them will learn the truth that will change their perceptive positively 👍.
Tako je
We are taught the periodic table of elements when it's a world of isotopes, neither idea or the science is wrong, but it's complicated.
He is more Knowledgeable than Him, not smarter. Dr. Walter may be right, just like what Mehdi says.
Maybe he was trying to challenge some unknown genius to step forward and call him out??
wish that was the case, but no. Watch my next video on this... hey did you call me a genius?!
@@ElectroBOOM Good catch! I saw the next video, too. You have inspired me, after binge watching all of your videos in one week, to finally start my new channel I have been thinking about for about a year (and to do some of your builds starting with the rolled capacitor). I may not agree with all of your politics, but I still think you are a genius :)
@@ElectroBOOM CAN YOU PLEASE GIVE ME A MULTIMETER OR RØDE MICROPHONE PLEASE I BEG YOU !! PLEASE !!!
@@arshuarshaq5043 FO Beggar
@@Akarsh- mind your words ! And he is a teacher to me !
What I got (reinforced) from this is that even the wire is a circuit component. Since the sense wire folds back on itself and follows about the same path back around, it induces nearly equal but opposite current from the wire that it's adjacent to, cancelling itself out. So you only read the effects of current through the opposite resistor. At least, that's what appears to be happening. He touched on that near the end when he drew in the hidden transformer.
From another Electrical Engineer- you got my vote👍
I've got an awesome relatively easy invention in electronics. would you be interested in a collab for improving the design, etc? maybe even patenting?
my vote too
As ways Mehdi>pedophiles
I am really glad you did this video, not just cause I agree with you. It can be scary to challenge the findings of someone you respect but I think he would respect that challenge because we'll science.
Unfortunately dogma is big in science as well. Look at the oil drop fiasco.
Can anyone show me where the professor says that Kirchhoff should be changed because it is not correct, and where exactly is the experiment that he did and that he says shows this. Why are people pretending that the professor is attacking Kirchhoff. It is clear that what he is doing is showing his students that when you make an experiment where you don't take into considerations the very well known limitations of Kirchhoff, you will get the wrong results. Not probing in such a way as to make Kirchhoff work was the whole point of the experiment. It was to show that not adjusting for the effects caused by the limitations will produce bad results. I am absolutely dumfounded that people legitimately thing that the professor doesn't know how to probe a circuit, instead of thinking that he is doing so intentionally in order to show his students the dangers of not fully understanding Kirchhoff laws and their limitations.
The first serious video in this channel 😂
A lot of love to Elctro Boooom
Came across your channel by accident, it took a couple of videos but ya grew on me lol.
Love the honesty, if ya don't know or not sure you say so.
Great job dude
You were totally respectful and very educational with this video. The net result is more people learning about electronics, so I think this is a wonderful video.
Agree! I've studied EE and I've come across this particular subject. I just assumed the lecturer was right at the time, but Electroboom got my gears grinding again, which is probably his goal.
Hi, I'm a theoretical physicist. I don't think Prof. Lewin was completely wrong, but I don't think your reasoning is wrong either. I agree with your calculations, but I think you are not applying Kirchhoff's law as is usually understood from the physicist's point of view. One may argue that Prof. Lewin is also wrong for the same matter when he says that Kirchhoff's law is sometimes wrong. It is never wrong: it's just that it does not apply on certain systems. In the end the problem, as I perceive it, is a semantic and not a physics one.
What I am certain, though, is that Lewin proved himself to act rude and arrogant in that comment box. Your objection was completely legit and he had no right to call you an uneducated.
As a mechanical engineer and amateur electrician, I was here for type a comment like this one literally. I totally agree with you. Dr. Lewin may right about KVL is not applicable on some circuits but that doesn't make the law "wrong" because it is not a theory. It is a "Law". Even if Mehdi is not right at all, it is not ethical to call him "uneducated".
As an asshole. you were all wrong.
@@tealiedie So Mr. Asshole. What is the truth? I am looking forward to.
@sudan suwal Mr. Suwal, please could you explain which argument that I posted above wrong? I am really wondering it. Actually not intend to kidding. I just want to know if I misunderstood something in electrical circuits. I'll be wait for your response. Good day.
You are completely right.
The professor is making the mistake that measurement of an experiment has to be the same regardless of the probes.
The fact that you get different results measuring the same thing means that something is wrong with the experiment,
automatically any conclusion is wrong.
Testing Kirchhoff's law in the professor ‘s experiment is the first mistake.
The conclusion is a ridiculous mistake.
I’m a professor so I can say what ever I want that is no mistake.
That is a fact.
Oh, I worked in that field - years ago. The KVL is derived from "E = -grad( phi )" and the corresponding integration theorem.
If there is an time varying magnetic field, the true electric field is "E = - grad(phi) - (dA/dt)" . I.e. the KVL holds in the electro-quasistatic approximation assumption, that dA/dt is approximately 0. The KVL is false otherwise.
It's very brave of you to challenge someone like that. Keep it up
Great scientists admit when they are wrong and let everybody learn from their mistakes; those other scientists get their ego punctured.
Indeed. Science is about the continually challenging and testing ideas and theories. Peer review is a cornerstone.
If you refuse to permit your claims to be challenged then you're a religion!
It doesnt necessarily have to be ego, but it can be very deeply rooted ways of understanding the principle. Especially for someone who does nothing but this for decades, you cant just step back and view it anew.
Nope. Walter Lewin is a great scientist, but great scientists are still human beings and still get caught up on personal bugbears that don't hold up to scrutiny.
This is a risk one encounters when delving outside of ones field of expertise. By ignoring the transformer created in his model, Lewin made a mistake that you clearly identify. Well done!
Electrical Engineering is Applied Physics but I get your point
I came to the same conclusion before even watching this video:
Spooky phantom transformer
In true internet popcorn fashion, I'm trying to find out who's winning the argument here but I'm not reaching a quick answer. For example, I'm not certain Lewin ignores the transformer issue. See freepdfhosting.com/d5fc27ec92.pdf for the notes accompanying that lecture 16, check out Test 1 and Test 2.
@@jimmoriarty6964 but the dude's field of expertise is astronomy
@@clusterfork
I think where this came from is that Dr. Lewin forgot to also include the transformer coupling to the wires that go to his oscilloscope. He sort of assumed that his oscilloscope is directly observing the voltage at those points.
Or it could be that be knows what is wrong perfectly well and uses this as a way of finding the really bright students that figure out why this happens.
Kvl is a simplified form of Maxwell's equation obtained by lumped matter discipline in which we assumed dphi/dt = 0 I.e zero change in flux.
Electrical engineers compensate dphi/dt change by taking into account inductance/emf on equivalent schematic. dPhi/dt exists as voltage induced in the coil/wire. So electricans actually use... Maxwell equation with dphi/dt "hidden" as emf and everything works perfectly. So... they both wrong?
Very well described! I work with small signals from microphones and phono cartridges and your video explains extremely well what happens in low inductance and low resistance loops and induced currents. Well done!
I was working on this same experiment for a Book. And I couldn't find a Simple way of explaining this. You did it in just 15 minutes which is awesome.
This is very well done and quite diplomatic I must say.
Well he works in electronics & has an MS in it.
Do you really think that his explanation is right??
Not to be rude, but maybe you should wait with your book until you know what you're writing about. Mehdi is completely wrong, and what he is proposing is in direct contradiction with maxwell's third law. Kirchoff's voltage law does not hold under varying magnetic fields and has never in history been thought to. As a matter of fact, if it did hold generally we could not have engines, generators or electromagnetic waves. If you believe in the existence of those things I suggest you take another look at the theory.
What mehdi did was to 100% verify the effects and then without much of a reason just dismissed them as "probing errors". They were not probing errors, they were vital parts of the experiment. If only it was this easy to disprove electromagnetism. I bet he would "disprove" gravity by showing a falling ball and saying that if only the gravitation didn't cause a probing error it would just float there.
I like how your comment says "very well done and diplomatic" almost exactly the same way that other guy's comment says, and he posted his comment a day before you... COMPLIMENT THIEF AHA
You're stupid
Great discoveries are made by those who question the leaders of the field
@LonerWolf Patriot That's the most ridiculous thing I've read today. Theories are never against reality. That kind of thinking bottlenecks our progress in science.
@@nullbeyondo No theory describes reality perfectly, it is pretty obvious he talks about science's continuous ability to find better and more precise theories by challenging its previous ones all the time.
@E it's not about being right or not, it's about testing, challenging and learning, that's the entire point of science. And most of the things ever tried don't work, but when they do, then we move forward, slowly but one step at a time.
Any good teacher knows this.
@E I think he is, tbh. Old people become so bonheaded that they refuse to listen to younger people.
And for Dr.Lewin to call him uneducated when his arguments are valid is immoral and i don't like him for that reason...
It's like trying to tell an old mechanic that what he is saying is wrong, they will just scoff and say "i have been doing this all my life so you can´t teach me anything"
@@PonaHD ElectroBOOM said some things right and other things wrong.
Here’s one example, said at least two times:
10:54 Nope, the voltage across two points in the presence of a time-varying magnetic field is not unique. Theoretically (if you’re computing the induced voltage), the induced voltage depends on the path taken to compute the line integral of the electric field. Practically, it depends on how you position the cables of the probes, as Lewin and EB showed in their respective videos.
You may say “it’s bad probing”, but I’d reply the following. As was demonstrated in the videos by Lewin and EB, voltage depends on the two points as well as the path. Now I ask you: “what’s considered the correct path to measure an open-circuit voltage, and why?”. I think the answer is: there’s no wrong path, all paths are correct.
11:48 Wrong. There was *always* two different voltages across the two points. Again, voltage depends on the path taken when computing the line integral of the E field. What you claim to be "the only voltage between two points" is actually the voltage assuming a particular path; assume another path and you'll get a different voltage.
---
Here's another example:
8:41 In the circuits being studied at this timestamp, certainly the RL circuit with the switch and battery acts as one winding of a transformer, and the circuit with the two resistors only acts as another winding of the transformer, so EB's explanation is correct here. But what if instead of creating the time-varying magnetic field with the RL circuit we instead create it with a moving permanent magnet? I wouldn't consider the magnet as a primary winding of a transformer, would you? So in this case we can no longer consider the circuit with the two resistors as the secondary winding of a transformer. So EB's explanation is no longer valid.
This video illustrates why I subscribe to your channel. While the majority of your videos have an important entertainment value, they're based on scientific principles. I appreciate the level of critical thinking you are able to apply to the many scientific laws of electricity. Thank you for the work you put into your videos.
Sadly, he missed the point of the proffessor. By definition KVL wall is not akways true, BUT you can fix that in practice. From scientific point of view the proffesor is rigth, from practical point of view it does not matter or almost
I agree. I'm an OLD electronic tech/engineer and have seen this sort of thing come up as a problem in a industrial installation.
I like how respectful this video was towards one of the greatest minds in out current time. Its not bad to disagree with someone and politely explain why. This is a great science video with awesome explanation AND a great guide to social communication. Good for you EB!
"Current time" !!!!
Smart guy yes, but one of the greatest minds of our time? Hmm. Hardly Stephen Hawking.
He is fuckin' smart, but far from the greatest minds.
@@88werwolfhun88 that why I said "ONE OF the greatest minds". Otherwise I would have said THE greatest mind.
If Lewin was so smart he wouldn't have been stripped of his emeritus professorship for sexually harassing students.
Arguing about incomparable achievements is pointless. So is the fetishization of hands-on knowledge. Takes all sorts to make the world go round.
would it be possible for you to start a lecture series about circuit analysis? i believe you are the best teacher i know. theory combined with actual applications/experimentations is the best way to learn.
i haven't been bored in any of your videos. you're so good! more voltage times current to you sir!
That would be great...
Bring this to the top, people! We need more Electro101 videos!
My god..... How about you stop writing cheesy comments and go and force times distance.
I'll support this ❤️
Ramon Cristopher Calam this would be highly appreciated!!!!!
This is a very good point, though several times before when I watched the video but didn't realize how important it is. The matter of this question is how to model the real physics system: we can model the magnetic field by inductances and transformers as electrical engineering, while physicists may look at PDEs and have less emphasis on lumped circuits. As for the probing, that's another vital lesson I have learnt, because I was lucky enough that I didn't burn the scope with ground circulation with two passive probe at a region of high di/dt, quite similar as here.
I am a law student who desperately wanted to study physics. I've searched for law stuffs, and RUclips suggested me this. Thanks to RUclips for realising my heartaches.
Ouch, love of physics is really strong
So did you quit law to study physics?
May I suggest an alternative test for probing this circuit:
Rather than having the probe wires in the same plane as the resistor loop, instead have the wires perpendicular to the plane of the loop (parallel to the changing magnetic field). Thus, no EMF would be introduced into them until they are sufficiently far away to make the effects negligible.
good girl
The alternative would be to use a real transformer and a AC supply...but clearly electrical engineers already know how transformers work.
also suggested that way, then prob won't affect by EMF
I will try this later this week
The probes in walter lewin's experiment are not affected by the changing magnetic field already, because in the external loops there's not much going on, there you can safely apply kirchhoff's loop rule and that's why you can measure Vr1 and Vr2, because the same voltage is applied on the scope
You are correct I have experienced different measurement around the loop while performing some practical in my university even my professor were stoked to see that, but I realized later that I had bad probing.
Well explained Keep the videos coming and always express it good to see what other people think.
try probing shitty solder joints with a scope......you can get readings from 0 to 150V on a 5V circuit.....
90% of people who liked this comment saw just some smart words and liked even without reading
@@tarike5613 You sound like a stupid person who can't read. This person's comment is clear.
@@laharl2k yes
@@SpaceTimeBeing_ i though the comment was pretty clear to,weird.
Two truly good and decent men struggling to teach the next generation!.. they should be proud of each other!.. Im proud of you ElectroBOOM!
Amazing video, and bad youtube algorithm, even tho i been watching your videos for ages (and subscribed) this good quality video was never in my feed... found it by mistake, and i was like “this must be new upload- just to see it’s 2 years old”
This and the follow-up part 2 video are my two very favorite videos of yours! Your passion is for the science itself...finding the truth...This is the same passion, Faraday, Maxwell, Feynman, and the other greats all shared...You're in good company! Thank you for this series and for the inks to the counter-arguments by Lewin...
"My mom thinks I'm mostly OK" Words to live by brother.
Hi, I think that what you are missing is that is not always possible to consider an inductance to modem the changing magnetic field. For example you could consider a magnet moving near your circuit.
From a mathematical point of view maxwell’s law says that the integral of E in a closed loop (which in electrostatic is the ddp) is zero if and only if the flux of the magnetic field is constant through the surface enclosed by the loop.
Anyway very interesting video thanks!
YES! I saw the transformer, too. The sense lines are part of the circuit! (I was just an ME, not an EE, although I am a licensed ham for what that's worth.)
I will watch this in front of my family, so they will think I'm smart
😂😂
@@animeshpathak3921 Really? Come on there is no need for that, Apologize.
Ok.
😂😂i think that i am the only one
Clever man😂😂😂😂😂
Being an accomplished physicist does not preclude him from being wrong.
But he happens to be right. Its not hard to see that inducing current round a loop means the voltage also goes up round the loop one-way, so can never sum to zero.
Being a youtuber does not mean you know how to teach. The professor was giving a lecture to students, and showing them how not knowing the limitations of Kirchhoff, will produce wrong results. He made an experiment... he did not take the limitations into consideration (he did not correct the result by use of clever probing)... he obtained the wrong result... he showed his students this fact... his students now remember that the limitations need to be taken into consideration and do correct measurements or whatever. That is all. All these people on youtube showing how the experiment should have been done, are completely missing the point of the experiment.
WoW ! - I feel like I'm watching two gods fighting each other on mount Olympus and I have a BSEE degree.....
Studying electrical engineering and watching your videos is the best combination
I love this about a person of science. Challenge even the most established idea. Your humble nature shows, and is really appreciated. Good vid, as you demonstrate how the exact positioning of sensory wires makes a massive difference.
Howwwwlyy Shhieeeett!!
When I heard "2 different Voltages across the same 2 points", I questioned my life and all circuits that I ever made ^^
Now that I saw the great explaination it all came together for me.
But I do agree with you. It does make a lot on sense when you think about it.
You're not alone.
i like this way of experimentally trying to prove someone wrong. It's a nice and a humble way to disagree with someone of such high caliber.
I know nothing about this yet i enjoyed it thoroughly :)
Yeah me tooo I don't understand either since I got my masters in maths but still is enjoying it
As a medical student I have no idea what I'm doing here lol
It’s the mystical power of his eyebrows 😂
you are not alone dude..hahaha
😆 well you did learn something!
Same.
When you have to use a defibrillator this might come in handy.
New to the channel (probably one of the best RUclips channels yet). Love the video! and as an EE student, this totally makes sense, and I couldn't agree more. Keep them coming!
I love you electroboom really love your video. Thank you
Absolutely agree with ElectroB! Thank you for the thorough analysis!
Dear Mehdi Mercury, I am (was) an electrical freshmen. After watching all your videos over the weekend, I decided to switch to Business & Management because I can no longer solder or plug in something to the outlet without imagining sparks.
Lol
Well that's a negative effect.
Don't worry, this panther will carry the EE torch.
Uh, if you get different readings, dependent an moving your scope/sense wires around, that might be the hint, that your sense wires and scope position are not just sensing wires, but part of the circuit you created.
Exactly. Needs a bigger model
yep， as long as there is an alternating magnetic field through those wires. there is going to be an issue. Try with shielded wires and that will work
Yeah, I don't get how Walter Lewin didn't see this. It's something you learn really early on in physics, and something that definitely shouldn't make you think that something like Kirchhoffs Law is broken.
Yip, pretty fundamental from an engineering prospective. Change the probing arrangement, get a different result, then you know for certain that your probing stinks. Don't understand how Walter considered the probe wire as miraculously independent of the main loop and that running it close to the main loop was all that was required to prevent pick up. As an engineer, even the small loop between ground and tip of the probe can give you all sorts of nefarious results, never mind a 2 X 2 inch wire tied to a loop, forming another loop with the other half of the main one!!!!! The problem Walter has is that the integral of E.dl gives the INDUCED EMF. Walter is arguing that this is the ONLY EMF present. Nope and nope. This is akin to a free energy device and we know how Mehdi loves those!!!
His simplified circuit and it's readings should be the final QED on the subject.
@@bleblo13 I love watching Walter and I'm going through 8.02, but just watched his lecture on ohm's law, which, interestingly, he gave the same treatment as KVL. His argument was because a light bulbs resistance changes with time, because of temperature, then it's not much of a law.????? I think he's got a bone with lumped model stuff, hence this and his KVL statement, even though KVL is based on the conservation of energy!
I’m sorry to say that Veratasium’s video on how electricity moves through wires and also your discussion with him on the topic, helped me immensely.
I am currently reviewing for my BSEE licensure exam. It leads me to this guy.
I fully agree that the model is missing an inductor. The ability for a wire to be able to have current induced from a changing magnetic field needs to be modelled in the circuit as an inductance. Just like the lumped element model for transmission lines.
Exactly.
Every wire with a length longer than zero has inductance, no matter how low its resistance is.
Had these been ideal wires with 0 inductance would mean they have to also have a length of 0, this would make the diameter of this circle also 0 giving it no magnetic loop area and making it impossible for a magnetic field to induce a voltage in it, hence voltage on all nodes would also be 0V. This then matches up with the circuit of two resistors, there is no component capable of creating a voltage.
But where does the inductance go in the circuit? It is distributed everywhere in the loop, including in the resistors. Lumping it in a specific place is not an accurate representation of what's going on.
@@Steve-du6ms Each resistor can be replaced by its resistance and a series inductor (ESL).
Each real life wire can be replaced by a resistor and a series inductor (ESR & ESL).
These elements are joined together with circuit diagram wires, which have no properties in real life.
@@@Steve-du6ms
Every length of wire in the physical circuit would be replaced by a inductor in the schematic with a value equal to the amount of total loop inductance it contributes.
Additionally all these inductors need to have a arrow drawn between them or a line along them to indicate they are coupled inductors that share the same magnetic field and each inductor should be given a dot at one end to indicate it going clockwise or counterclockwise to this field.
When the probe connections are moved around to the left or to the right of the circuit this causes them to flip from going clockwise to counterclockwise, this flips the dot on the inductor, indicating it will create a voltage in the opposite direction hence why the probes going to the left or to the right side produce a different result on the oscilloscope. Once you include all these inductors the sum of voltages equations you should get a pretty close match to what the oscilloscope is showing.
EDIT: Oh and you also need to include the inductor of the solenoid in the middle, it is also coupled to the common magnetic field and is connected to a voltage source. That is the voltage source that is powering this entire circuit.
@@berni8k The inductance needs to be added everywhere in the loop. This means that the voltage is induced everwhere in the loop, even within the physical resistors. So the model would include many, many mini-inductors, each with an induced voltage. The difficulty I have is that this cannot simply be lumped in a convenient place. So it is not obvious to me that the neat KVL circuit, with a source and lumped elements, emerges nicely from this situation.
Why do I watch this? I understand nothing.
I've asked myself that very question.
I'm as smart as a bag of rocks. All I hear is scientific gibberish
@@johnfarris6152 If you don't understand the terms you're learning nothing our minds are great but they're not magical
just learn 4Head
I’m trying to learn through osmosis.
lol
7:12 thats good one.
I don't want to take sides but Dr. Lewin's reasoning is sound. KVL as we know it from (lumped) circuit theory can be derived from Maxwell's equations as a particular instance. If the magnetic flux enclosed by the circuit (contour for the path integral) is negligible then the voltage produced by it is negligible and we get the known KVL for voltage. This is much better explained in Harrington's "Time harmonic elmag fileds" with a nice summary in Table 1-1.
You just invented Polite Roasting
He lives in Canada, eh? :D
Electric Blanketing, then?
That's been a staple of good science since forever..
Like a true Canadian!
1:20 everyone.
Imagine this world if just more people had Mehdi's scientific and philosophical humbleness
@@therealb888 that's racist
Thank You Sir Engineer.
You kept me even more curious in electronic world.
I am so amazed with your videos.
I hope to master all the basics and to starts doing advance.
10:03 I love how he says " half-e-Vee" thats the Pinglish (Persian/English) translation of "half of V" . I love it because I do the same thing when I'm doing circuit analysis... add lots of farsi profanity.
I remember having a similar conversation with one of my instructors as well. He simply said, high tolerance applications, use Kirchhoff's Law. For low tolerance applications, use Faraday's Law. I doubt I would have caught this.
This clears up a lot for me.
Serious question: how is it possible that such a fundamental question doesn't yet have a solution that the scientific community agrees on? It looks very weird that nobody has encountered, and explained this before with some sort of peer review or it's just Lewin getting it wrong?
Yes
Seems like Lewin is the black sheep in this debate. As both Lewin himself and Mehdi note, the majority of literature suggests that KVL holds in general.
Makes sense then. Cheers
@@ElectroBOOM /r/inclusiveOr
@@ElectroBOOM regarding your video for the charged comb
No i don't think that current flows just because thecharge is moving .but the question is that if the current flows where would the charge flow to . there must be a circuit or path for the charges to flow and be considered current .for example take the case of me having a battery with me as i travel in a car the battery had charges and the car is moving that would not be current .
I'm really confused can someone explain me where I'm wrong
Thank you for contributing in the peer review process.
bro curl(E)=-B_t (where B_t is partial derivative of B with respect to t) is a maxwell eq. it is always valid. while applying kvl u assume that E is grad of some scalar function, if a vector field is grad of a scalar func, then it must be curl free. however we know that curl(E)=-B_t, thus kvl is not always valid, which assume curl(E)=0.
8:53 Dr. Lewin ended up not being a nice guy
@@outros5062 is it real
@@anantapadmanabhmyatagiri you have internet. Try look it up. As far as the time goes, it is real.
@LonerWolf Patriot your reply made me laugh so hard that my ribs are paining now.
He's a damn good physics teacher..... that's it! He's not a good person at all, just watch his interviews( search physics wallah walter lewin interview)
Damn, its like learning that Conway is a raging asshole who hates everyone and everything (especially the thing he is most famous for).
I had been wondering about Dr. Lewin´s experiment since the first time I saw it. I watched it several times and had come to a similar conclusion.
Since this is an air core transformer, any nearby wire is part of that transformer. Magnetic fields can have very complicated effects.
Basically I´m glad you adressed this.
Kirchhoff's law holds only in cases the circuit size is much smaller than the wave length that passes through the circuit from the source. This is called a Quasistatic approximation, wiki link below.
The simplest example is an antenna:
An antenna broadcasts an electromagnetic field to the environment by a changing current that runs inside it. If Kirchhoff's law was true, there would be no current running through the antenna (it is cut off by KCL KVL laws).
en.wikipedia.org/wiki/Quasistatic_approximation
@@noamgraham9006 no that is not true at least not fully. Also there is also the possibility of "short" antennas that are smaller than a quarter or half waverlength. but that is not what lewin is trying to show. here he is not working in HF areas
What a legend man, I only understood half of what you explained, but I could tell that you were serious about it!
Well, you very ably guarded the principles we(i say we for the viewers), have learnt in our science and engineering subjects. Keep up the good work! Would have loved to watch your videos growing up. Would have definitely helped to score better!
Why don't you churn out a thesis paper on this?
Because there is no dispute. All he did was replace the changing magnetic field with a transformer to make kirchoff's laws work because you can remove the magnetic field from the circuit. Thats nothing new
Some of the biggest idiots I know have doctoral degrees.
Because he isn't proving anything new, like he said most of science agrees with him but Dr. Lewin does not (but he didn't write a paper on it), so simply he's disagreeing with Dr. Lewin's disagreement with this law in physics.
that's all well and good but perfectly acceptable and _useful_ papers have been written on less.
Science needs rigor, and a paper isn't pointless just for confirming something widely believed to be true.
@@DrummerRF The argument is that there is a "hidden" inductor created through the measurement device, is it not? Which is why this is up for discussion in the first place. Proving that through math and experimentation surely could have a paper written on the results. Doesn't necessarily need to be a thesis paper.
It was an excellent demonstration of the importance of considering all the details in a scientific experiment. In the demonstration, the hypothesis is raised that the consecrated Kirchhoff's Law could be nonsense, depending on the side where the instrument that measures the same induced voltage is positioned - an obviously absurd hypothesis. If the measuring instrument (oscilloscope) is to the right or left of the same circuit, the voltage reading should be the same - but in the demonstration it did not occur. Thus, the hypothesis that the said Law would be flawed was proven. The layman certainly went unnoticed that in both measurements, right and left, the circuit was not the same. The circuit, in fact, is not only what the demonstrator draws, but also the wires, cables and the internal impedance of the oscilloscope should be considered. As it is electromagnetic induction, any opening between wires will have voltage induction by the variation of the magnetic flux that surrounds them. The measuring circuit, to be the same with the instrument on the right and left, should be what was drawn by the demonstrator at 12:04. Soon after, he shows in practice that he did not follow what he drew; leaving again a new half turn wire near to the experimental loop over the magnetic field generator. It was an excellent joke of illusion. Thus, the hypothesis of failure of Kirchhoff's Law can not be confirmed.
Hello sir, I’m not sure if I’ve understood your video but in my opinion what professor lewin is talking about is maxwell’s equations. One of maxwell’s equation says that in presence of changing magnetic fields, electric fields are no more conservative therefore the work you need to do to get from one point to another does depend on the path you take and potential difference is just the work you have to do divided by the charge you’re holding
Why am I finding my Physics Guru 8 years after I left my school. Absolutely brilliant demonstration man.
I watched that class a couple of years ago and I found it very weird. I assumed he was talking about some advanced definitions and that the model of the "imaginary" inductor as a voltage source was a way to make KVL work out for induction machines. Now I feel so much satisfied with your reasoning ♥. Also I like to imagine the straight wire as a collection of tiny inductors in series, even the resistor itself acting as one, so that is NOT ok to assume 0 voltage drop just because the resistance negligible
Mehdi is soo near to 2M...
He is a electronics channel not chemistry how can he be near to 2 moles?!
@@alanwolf313 hahaha
And every single one of his subscribers is probably a uni student
@@alanwolf313 Lol, That's BRILLIANT!
@@alanwolf313 M actually refers to the concentraion c , M = Molarity
I think you nailed it. It would be cool if there were some kind of miniature surface mount circuits that you could insert around the loop that would transmit the value of the current instead of trying to probe it with leads. Instead of measuring the voltage what would happen if you measured the current around the loop instead with a tiny torrid with a winding on the torrid going to your scope?
The voltages indicated on the two voltmeters are the same irrespective of whether you measure directly across the resistor bodies or across the common connection nodes (where the differing measurements are disputed). In either case you get the ohmic or IxR voltage drop consistent with the adopted measurement path. The ongoing dispute about what is the "true" voltage difference between the common connection nodes relates to the matter of distinguishing between potential differences and transformer induced EMF'S. These two different quantities can only be separated by a suitable and unique arrangement of the measurement path connections between a voltmeter and the test points on the circuit loop. Strictly speaking if the resistor bodies occupy any non-zero portion of the loop path, the indication on a voltmeter connected directly across its terminals must be a combination of both electric potential difference and induced EMF. But the ohmic or IxR voltage drop is always indicated. What most people don't appreciate or understand is why electric potential difference (PD) and EMF are different and what are their distinctly different origins in the Lewin experiment. PD and EMF have the same unit [the Volt] but they are not the same thing.
Would there be any point in adding special sensors or toroidal current transformers? None that occurs to me, as such devices would add nothing further to our knowledge of the physical conditions in the circuit.
Yes, if one believes that one's probing wires aren't effected by magnetic fields, then one can fool oneself into perpetual motion fairly easily.
Your explanation in this video is correct and a fairly good demonstration of why too.
From Maxwells equations, the electric field E = minus grad V minus derivative of magnetic vector potential A. Obviously, mathematically, the sum of grad V around a loop is zero (~V2-V1+V1-V2). The question is, does the voltmeter measure grad V or E or something else in portions where A matters. It clearly doesn’t measure grad V, because the result depends on how you position its leads. The magnetic field affects the leads of the voltmeter and induces an additional E, thus current, inside them, which depends on how you position its leads in this magnetic field. The additional E is given by the rate of change of the total magnetic flux (magnetic field times area) through the closed loop formed by the meter leads connected to some circuit element. So, even if your leads follow the wires of the circuit, when you flip their position perfectly, grad V changes sign, while the additional E doesn’t flip sign. So, to eliminate it, the loop of your meter leads have to be parallel to the magnetic field (zero flux).
A schooling in Metrology101. Step1: Check stray inductance, capacitance & noise. Step2:
Marry me and give me scope.
Great video, and the best part for me was realizing you "forshadowed" the answer right at the begging when you explained why you twisted the wires of the scope....whether you meant to or not haha
I'm a little confused-how come there was current induced in the probe wires if they were twisted to prevent that?
You are so right... Thank you!
As someone uneducated in the field, I came to the same conclusion before you finished talking. I would love to learn why you would be wrong as I currently don't see it. Your arguments make perfect sense to me. The probe wires are part of this experiment when it is setup like this.
I'd go a step further and say that this is one of the cases where the fact that components are not, in fact, ideal, mathematical abstractions of components comes into effect. The wires have resistance and inductance.
I came to the same conclusion already when watching Dr. Lewins video.
A wire going trough a magnetic field can't just be assumed to have zero voltage. No matter how low its resistance is, it will always have some inductance that reacts to the field.
I could see however that looking at it from a theoretical point of view one could come to such an conclusion. In such theoretical examples you can never include all parasitic effects because the whole thing would just become a mess that literally takes weeks to calculate my hand. Its easy to miss a single significant parasitic effect and still have the math work out and seam logical. While on the other hand me being an engineer who deals with practical problems i know that a trace on my circuit board is not a perfect ideal connection between two nodes. I know from experience when a SPICE cirucit simulation behaves strangely that i need to model in some non ideal or parasitic effect. I have been bitten in the ass before by "simply ignore parasitics because they are so small they don't matter", my circuits didn't work how i wanted and every time it happened i learned how that particular parasitic effect is important and how to include it into my design process. You can't remove parasitics by simply ignoring them, you can only understand them and design them in as part of your product.
@@skonkfactory Even if the wires were ideal with zero resistance, there would still be a voltage across them. There isn't a voltage drop being measured across the wire. There is a voltage induced in the wire due to magnetic induction. If the wire were ideal, it would just give you a more accurate reading. The mistake that was made was not treating the circuit like a loop, but instead as separate parts. If you were to do the same with a transformer, you would conclude that KVL does not apply since the voltage applied is much higher or longer than the voltage read. But we know better since the change in voltage is found by measuring the coils.
@@megamixa Right, exactly- the wires have inductance (specifically, mutual inductance with the driving coil).
@@megamixa An ideal wire would have zero loop area and zero mutual inductance. It would literally be a circuit node of zero dimension.
"If you do not agree you need to be educated...This is very very basic physics and I never argue with people who think they know but who do not... The stunning demo at the end of my lecture..."
His attitude doesn't mean he's wrong about this particular thing, but it does mean he's not worth listening to.
His attitude also means I'm not at all surprised about this:
news.mit.edu/2014/lewin-courses-removed-1208
@@87knox meh... nowadays everything can be considered sexual harassment if one lady decides it is one.
This attitude is simply badge flashing. Which is sad for a scientist.
In this case it is at least 11 women he was found to have sexually harassed, and my quick skim through Inside Higher Ed's January 2015 article on the matter shows that MIT was provided plenty of evidence and did a thorough investigation into said evidence
@@666aron not when the claim has supporting proof,
Read this www.insidehighered.com/news/2015/01/23/complainant-unprecedented-walter-lewin-sexual-harassment-case-comes-forward
Your "noise" measurements are the inductance of the two wires in parallel and EMF induced into the circuit and the untwisted portions of your lead. Reason why it differs is they are in different positions one time closer, another time farther away, or other times not totally parallel with each other. In order for you to get an accurate reading you should use shielded leads from point to point or have your untwisted leads, 90 degrees from the measurement point. And if you really want to get picky, the probe itself will affect your measurement as it becomes part of the circuit. Because, depending on the frequency and voltages being measured, you can introduce capacitance or attenuation.
I see what the professor is saying... when a circuit is being effected by EMF due to the circuit component characters, wire and connection resistance, until the EMF finally peaks, the circuit will behave and measure differently in different spots and will not equal zero. Depending on the placement of the EMF and the measuring devices you can get, either a positive or negative peak. You can see it in your noise measurement, those ripples are the varying voltages until the circuit stabilizes. Due to each component characteristics and connecting wire length the circuit at times, the total voltages will not equal zero.
In addition, EMF waves are formed in the circuit which can be out of phase until the circuit "catches" up. And you also have angular velocity, field flux, stray field and cross lines to account for until the field stabilizes. Plus, just arbitrarily setting the circuit over the coil doesn't allow for accurate readings...
When the law was written, they did not understand I-V characteristics, nor could they measure it or the circuit accurately.
Plus you are measuring with a single scope... measure it will multiple scopes and compare the timeline of the voltages measured in the circuit and you will see.
I connect a voltmeter between two points on a circuit and think "I'm measuring the voltage between those two points". I'm not thinking clearly. The voltmeter is indicating a response to the total electric field which exists along the path occupied by the voltmeter and its test leads - i.e. between the points being probed. There may be both conservative Coulomb electric field components and non-conservative solenoidal field components which comprise the total electric field along that particular measurement path. In the case where there are definitely only Coulomb field components (e.g. in simple DC circuits) we can justifiably claim what the voltmeter indicates may be interpreted as the voltage difference or potential difference (PD) between the two points being probed. If there are induced solenoidal field components present along the measurement path, what we think we measure and what we actually "measure" may differ. This is what the Lewin experiment demonstrates quite clearly. Voltmeter indications in the Lewin experiment are ambiguous. Even if we closely align the measurement path with the actual path via the circuit between the probed points, the paradox remains unresolved - at least in the Lewin experiment case. There are always at least two possible paths between the probed points on a circuit. In more complex circuits the electric field conditions along the range of possible paths between the probed points will vary.
Where solenoidal fields are likely present we might try to circumvent any ambiguity by judiciously choosing a measurement path between the probed points which we assert includes only Coulomb fields. This may not always be practicable. We can measure the PD across the terminals of an inductor but we can only surmise what electric field conditions exist along the inductor winding & which give rise to that PD. It is physically possible to arrange the measurement path to probe what is claimed be the Coulomb field (scalar) PD between the two points on the Lewin experiment. However we are simply choosing another measurement path which is after all, one of a number (an infinity?) of possibilities - the majority of which give different results. Surely it's the electric field conditions along the circuit path itself that are important - irrespective of whether there is ambiguity in the voltmeter observations.
Dr. Lewin is displaying behavior far too common in the veterened engineering academics in that he clearly believes his knowledge and opinion is higher than anyone else. It is an unfortunate side effect of hubris in this field and I've personally experienced it in many professors. Simply in the way he responded to your comments, insisting that any argument is the result of no education and only his video and lectures can educate you, all the way to that last clip you showed where he reveals that every other author and professor disagree with him and yet they're the ones that are wrong? I recall a professor refusing to allow us to use Thevenin's equivalence when analyzing BJT circuits simply because she didn't like it. Every single online tutorial, university, and textbook insists on its use over 8 KVL equations but she didn't care because her opinion with gospel. Knowledge =/= education and that's incredibly important to keep in mind. You can have all the knowledge in the world but if you don't or can't question that knowledge then you're not well educated.
" insisting that any argument is the result of no education and only his video and lectures can educate you, all the way to that last clip you showed where he reveals that every other author and professor disagree with him and yet they're the ones that are wrong?"
Sadly sounds like the attitude you get from the likes of anti-vaxers and other conspiracy theorists. Even really intelligent people can fall into this trap.
Very good point. You can get a nobel prize (in STEM that is) but still end up talking nonsense.
Pretty insulting how he approaches Mehdi's request. Theres such a thing as confidence in science, but there is also blatant arrogance.
I was lucky. When I changed career (I got bored with electronics as a profession as it takes 2 hours to design something then 8 months to do the damn paperwork). Several of the lecturers who were international leading experts in their fields said roughly the same thing: "This is my educated opinion, there have been many other educated opinions over the years that have been ultimately proven to be wrong. Remember the same is true of my opinion - just because I have a PhD does not mean I cannot be proven wrong at some point in the future." Basically we got marked on how many differing opinions we engaged with and how we analysed the evidence. In my dissertation I even got my supervisor questioning parts of his own PhD thesis.
Reminds me of medical academia. Most doctors today keep treating patients with medication that just makes them worse. Diabetes, for example. Countles and countless of cases where it's reverted by change in diet but they refuse to even take a look at it. Makes you wonder if theres a big pharma mafia after all. Fortunately there are more and more doctors leaving their ego at the door and raising their voice.
The way you explain it, it seems so obvious, but I have a Master's in Civil Engineering, so what do I know? I studied water.
Solomon Parker There must be something wrong. I was under the impression that civil engineers studied only concrete and steel
Water flow is immensely more complex than this to me. Even as only a second year Electrical Engineering student, I look at Dr. Lewin's lecture and immediately sense something wrong, despite how experienced and knowledgeable he is.
However, if literally anyone told me anything about pipes and flowrate and stuff I'd probably believe it because fluid mechanics is a complete enigma to me despite having had to take it twice
@@smlgd There are four main disciplines in CE. Structural (what you speak of) Transportation (roads, pavements), geotechnical (soils, landfills, underground structures) and Environmental (water, wastewater, air treatment). Had to study them all, focused on the latter.
@@BonJoviBeatlesLedZep Water and electricity are very much analogous on the basic levels, until you get to things like EM fields and capacitance and the higher stuff.
Water is important too. Possibly more important.
hahahaha I really enjoy your videos, amazing analysis, keep on working, nice job.
Did saw the Prof. WL video, was shocked momentarily. Later felt convinced. With DC source direction of electric field outside and then within the battery is in opposite direction, however in the second case direction of non conservative electric field form a closed loop.