Does Kirchhoff's Law Hold? Disagreeing Professor Beats Student 2 months ago   13:21

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:

By: Mehdi Sadaghdar

#Kirchhoff #KVL #KCL #ElectroBOOM

Comments 3901 Comments

Hello team RECTIFIER! Make sure to watch the next video on the topic:
CLLLICK! subscribed :)
Vijay Kumar
Hi ElectroBoom, Please make your opinion after watching this video
Erik Olander
Dr. Walter Lewin is trying to say weird thing happens with magnetic fields. But he uses bad way of explaining physics. He uses a definition of voltage that changes when probed in different ways. This is confusing. He should either make a more advanced explanation with vector potentials, or a simpler one like ElectroBOOM.
I have no idea whats going on right now. Guess I need to watch more videos on kirchoffs law to understand
Michał Borkowski
"My mom thinks I'm mostly okay" I think you're okay too
Ed Fallon
You just hurt me with knowledge. Thank you, it was excellent.
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:

*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?
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:

Differential Form:

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

Apologize to the Professor.
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😁
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Professor Beats Student Does Kirchhoff's Law Hold? Disagreeing 2 months ago   02:43

Professor Walter Lewin of MIT beats student in science demonstration.