Re: induced emf again

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Wed, 1 May 2002, Ludwik Kowalski wrote:

> ... I can IMAGINE a "flexible circle" wire loop whose radius
> changes to create an induced emf. The symmetry argument could
> be used to argue against any charge density gradient.

Of course, because, as you have noted, a charge density gradient
(along the circumference) is precluded by symmetry.

> If no gradient is needed in a circular loop then its presence in
> a rectangular loop can be questioned.

You are certainly *free* to question the presence of a charge
density gradient in an asymmetric situation whether or not you can
point to its absence in a symmetric situation, but I don't see why
you would.  Is there any other way to explain why the same current
flows in each of the four straight legs in the "moving rod on a
rigid frame" problem?

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm