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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#Kirchhoff #KVL #KCL #ElectroBOOM

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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

"(...) 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!*

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.

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