Does Kirchhoff's Law Hold? Disagreeing Walter Lewin demonstrates moment 2 months ago   13:21

ElectroBOOM
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:
https://up-tube.com/upvideo/aTDoN2wjxJV
https://up-tube.com/upvideo/YmG_LM0kPSL
https://up-tube.com/upvideo/jm_TdB-Hex4
https://up-tube.com/upvideo/s3-FsmrchCf

By: Mehdi Sadaghdar

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#Kirchhoff #KVL #KCL #ElectroBOOM

Comments 3818 Comments

ElectroBOOM
Hello team RECTIFIER! Make sure to watch the next video on the topic: https://up-tube.com/upvideo/D9YhIOsjimN
M Ismail
You are hilarious, wish I discovered your channel during collage. you would have saved me alot of time
Nonononono Ohno
My translation of the *ORIGINAL WORK BY KIRCHHOFF FROM 1845:*

"(...) it becomes easy to find the requirement, which [voltage] u must fulfill, so that the electrical condition on the [metal] disk can be a stationary one. When we look at a closed loop in [the disk], inside of which *no electricity is being fed into* [the disk], then the sum of all amounts of electricity which flows through this loop must = 0, which means it must be: *Integral of (ds dot du/dN) = 0* ... when this integral covers the whole loop."

The original text can be found at google books in the following link, book pages 497-514: https://books.google.de/books?id=Ig8t8yIz20UC

*Very obviously Kirchhoff had been aware of the prerequisite for his "loop rule", i.e. that d_phi(t)/dt must be equal to zero!*
tristan ginod
What he does not just put the probe wires in parallel to the magnetic field, to make a null vectorial product? And to avoid noises, just use low impedance coaxial cable, with shield connected to the ground?
David James
If you measure a voltage across a circuit that you think should be 0, but it is not, just recalibrate your voltmeter to show 0. Problem solved.
KSN's Tech Topics
You are absolutely correct, the discrepancy is due to the induced voltages in the connections to the 'scope. Kirchhoff's Law is not violated.
Gianluca Caliendo
where do you make your explanations?
DavidFMayerPhD
Re-learn Maxwell's equations. What Dr Lewin is saying is that Maxwell's equations are CORRECT. You are stating that Maxwell was wrong. Sorry, YOU are wrong.

Consider the simplest possible case. A closed loop of wire. No resistors. No capacitors. Just a closed loop of ordinary copper wire. If you then create a magnetic field in the loop, you will find that a CIRCULAR current forms in the wire so long as the field is CHANGING. This is the principle of the transformer. It is easy to detect this current using the usual clamp ammeter. Since each small piece of wire is carrying a current, and since the wire has resistance, there MUST be a voltage along the wire. That voltage does NOT amount to zero, because then the current would amount to zero. The relevant Maxwell Law is:

Integral Form:
https://wikimedia.org/api/rest_v1/media/math/render/svg/4323d83e3457e4a6b340b626d167b864884f38aa

Differential Form:
https://wikimedia.org/api/rest_v1/media/math/render/svg/2eb118e22c941e34f5537dbbdcaa3d7ba23603e0

The circulation of the electric field around a loop equals minus the change in the magnet field inside the loop.

Apologize to the Professor.
grpagobo
maybe you both will arrive at the same conclusion if you take into consideration relativistic effect and quantum mechanics hahaha.
Guillermo Sempron
You are correct. Lewin measuring is wrong.
Davidian Music
I would say your conclusion is correct from the start. I’m surprised that induction on the probes wasn’t considered earlier. And, is Dr Lewin wearing a licorice all sorts neclace?
Subhadeep Bej
Added to watch later!
John J
I now realize I'm retarded... Thanks
Amir Mahmoudi
Oh i knew you are iranian😂 happy to hear it here in this video😃 مرسی که هستی کلی ازت آموزش گرفتم😁
Rafał Kwiatkowski
In this case induced electric field has rotation that doesnt not equal zero therfore you are not allowed to use Kirchoff's law - Please educate yourself.
Hand Solo
Dr Lewin seems to be ignoring the "in a closed system" component of the law he's attempting to debunk.
Rickard Zakrisson
What about open systems, can one of the node have magic free energy be harvested then?
Twenty_juan 2
Sorry, i didn’t get that can you go over it again
Claude Abraham
If we add a voltage source to the loop representing induced emf, then, yes, KVL is upheld.
Otherwise, it is not.
Dr. Lewin is correct. What you just demonstrated is already very well known.

Claude Abraham
40 year EE
PhD student EE
Nagy Andras
i don't think you are right. you did not get a shocking experience so there was no voltage present.
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Walter Lewin demonstrates moment Does Kirchhoff's Law Hold? Disagreeing 2 months ago   13:58

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