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Re: induced emf again



Ludwik Kowalski Asked:

I am puzzled by motional emf (v*B*L) produced
when a metal rod of length L slides with the speed
v along the rigid wire frame perpendicular to the
uniform magnetic field B. The v*B*L formula
can be derived in two ways: (a) from Faraday's
law of induction and (b) from balancing two
forces. The second derivation bothers me it goes
like this:


If I recall correctly Einstein said that this was
a question that also perplexed him when he was a
student.

Anyway, doesn't relativity resolve the question?
It seems to depend on which reference frame
the observations are being made from. I believe
that from the reference frame of the sliding wire,
the B field is seen completely as an E field.

Ed Schweber