Kirchhoff's Loop Rule Is For The Birds

[anon]

Kirchoff: What's the altitude of Mt.Everest?
Faraday: Going up the north face? Or the south face?

[ThePontifical]

Professor Lewin, Thank you for your lectures, you are the feynman of this time. You teach physics as an art, and there's beauty in that. You have made me understand physics in such a beautiful way. Thank you for everything !!

[RakibulIslam-yzgn]

I can not explain in words how much I love your lectures Mr. Lewin!!! I just love it!! THANK YOU for all the intuitive ideas and all! You will always be my favourite physics teacher! Love & Respect! :-)

[paulsebring]

Even with my lowly AA Engineering Science I understand this instructor did not apply Kirchoff’s laws properly. The magnetic field is a current source that was not represented as a lumped element in the circuit.

[pacrii]

I'm so glad this guy is still around. I despised physics before him and Feynman.

[PHYSICSSIRJEE]

This result never ceases to amaze me, it's like reading a suspense novel again and again, knowing the climax but still getting 'goosebumps' at the final reveal at the end 🙂❤️

[mohammedridahasansaeed]

I learned somthing…… even after 30 years of teaching this to my student

[neu]

Sir I had a doubt if we define KVL to be the closed loop integral of Econservative.dl and set that equal to 0 then what's the problem in using it?

[scatteringer]

This is obvious, in fact we use lumped parameters (thus kvl) only when there are some particular conditions, otherwise we use distributed parameters (thus Maxwell).
Fortunately for a lot of simple pratical cases we can use kvl. But obviously not for all.
You can also modify the lumped topology in order to have some kind of approximation of the effect of the external field, for example adding a transformer, there is a lot of literature in the EMC sector about how to approximate these kind of effects using lumped parameters.

[ChancellorWiggins]

Great video, Professor Lewin. Thank you for all the time you've spent teaching!

[ramonchan]

Hello professor Lewin, I am a Chinese living in Australia. I first heard about you and saw you on Brian Greene's documentary "The elegant Universe". Since then, I have been seeing you from time to time on other science documentary programs, so I went to search about you and saw your amazing lectures that you posted on youtube. I was so impressed with your pendulum demonstration. You really did inspire a lot of students and made them love Science. Therefore, I decided to buy your book "For the love of Physics". Thank you for your contribution to science education.

[RajatBisht]

29:44 Hey anyone please tell that why is it don't want my concepts to be wrong and My JEE mains is near. Please reply
I didn't find Jason anywhere!!

[jeetz]

Hey there, Walter Lewin sir . I am in std 12, in INDIA we have kirchhoff law in our physics and I interested to know more about this law deeply and now I understand this law very nicely . So thanks a lot, you fulfill my interest on kirchhoff law. Thankyou.

[lecturesbywalterlewin.they]

*There are people who object religiously to the correctness of the mind-boggling demo that I do at the end of lecture 16 of 8.02. They all conveniently overlook that this demo showed PRECISELY what was predicted by my derivations. Two identical voltmeters are attached to the exact same 2 points in my circuit. The Curl(E)=-dB/dt caused an induced time variable emf in the circuit and consequently at any moment in time (my time resolution was 0.1 msec) voltmeter #2 showed values 9 times larger than voltmeter 1 and the two voltages had reversed polarities. END OF STORY!*
*Therefore, all comments and objections are meaningless and without merit; they are wrong at best. It's well known to all people with a decent background in Physics that in the case of induced emfs potential differences between 2 points in a circuit are not uniquely determined; they depend on the path. This is also the case in the closed loops of the secondary windings of ALL TRANSFORMERS! My demo can therefore easily be repeated using an AC power supply and a transformer (see website below). The ratio of the resistors in the transformer demo was a factor of 20 (in my case a factor of 9). Notice that the difference in readings of the voltmeter in the transformer demo was a factor of 20 (depending on the location of the voltmeter) as dictated by Maxwell's eqs. Unfortunately the reversal in polarity cannot be demonstrated with the transformer demo as it uses AC current. That's the reason why I decided to use an electromagnet (DC current); it shows the polarity reversal beautifully. I too, in my early days at MIT, used only 1 voltmeter which I moved from one side to the other as is done in the transformer demo. But two voltmeters simultaneously used in my lecture #16 with a time resolution of 0.1 msec is more impressive as students can then see the results (including the polarity reversal) of both voltmeters simultaneously.*

Transformer demo

Lect 16, 8.02

Believing and Science are very Different

[sujalkarnwal]

I am very thankful to you sir. Actually I am preparing for jee mains in India and your lectures helps me too much, once again thank you

[mikeballer]

I love your lectures so much as an EE. I recently took my professional engineering exam and your voice saying the closed loop integral of E dot dL is not zero played in my head when I was writing out the equation. 😂

[carlossoto]

Dr Lewin would the Poynting vector S considerations be consistent, that is with E and B appearing everywhere in the circuit ?

[rodrigoqueijo]

Im an industrial engineer student at Uruguay, and never ever was a proffesor able to explain this in a way like you did. Im really happy to come across with this video. Its clear that not many proffesors trully understund, or, if they do, the dont have the hability to teach in such a simple way the physic that explain this phenomena. Thank you.

[weejiechai]

KLR only applies for steady B field. Maxwell law of electromagnetic induction is more general and more powerful.


That is why in the 4 governing equations for electrodynamics....u see Maxwell law of EMI, not some KLR.


Prof Walter Lewin is correct.

[anuragmundargi]

thank you professor your lectures made by concepts stronger and helped me in iit preparations thank you so much u are the best