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Hi there!

I'm a first year student and found quite interesting the MIT on-line video lectures on electromagnetism.

http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/index.htm

In one these lectures given by Dr. Walter Lewin it is explained how all college books and teachers wrogly use Kirchhoff's 2md law in order to calculate the current through a RL circuit.

That is emf-IR-L (dI/dt)=0. Dr.Lewin says that this is the right answer but physically the procedure is not. In his lecture he states that Faraday's law is misinterpreted and not taken into account. He thinks that everybody knows that that's the differential equation, and just because they see a zero automatically we are using Kirchoff's law.

Lewin follows saying that Kirchoff tells us that the sum of V through a closed loop is 0, but how can it be zero if we have a change in magnetic flux. and therefore the closed integral of E.dl =-dflux/dt.

I couldn't convince my teacher. I am totally confused and don't know what to think.

What do you guys think? Is Lewin right? How can I convince my teacher?

Yours,

Santiago

P.S.: here's the lecture in PDF

http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/LectureNotes/index.htm

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# Kirchhoff's 2nd law wrongly used or not? Lewin vs all college books

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