Re: induced emf again

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

OK, I should have said that, as far as the induced emf is
concerned, the charge density gradient is not essential. It
occurs at every corner, not only at the ends of the sliding
rod. This brings me to the initial concern. One derivation
of the emf formula makes us think that the separation of
static charges occurring at the ends of the rod is essential
while another makes us think that it is not essential.

The second derivation ignores static charges, the first
treats a rod as if it were a battery in which charges are
separated. That is why I asked if somebody knows of
an experimental verification of the emf=B*v*L formula
for an isolated rod crossing magnetic field lines.
Ludwik Kowalski

John Mallinckrodt wrote:

> 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