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Re: Batteries



The statement occurs in the new version on page 730. Your concern is
certainly well founded if you are considering an electron moving as the
result of a magnetic field only...it moves in a circle, the force is
perpendicular to the displacement and hence the work is zero...and no
surprise the speed is constant. This situation seems a bit more complex
since the v referred to is not the velocity of the electron, but rather
the velocity of the rod, and hence the velocity of the electron as
caused by the motion of the rod not the magnetic field. The resulting
magnetic force is in the direction of the electron current, so it seems
to me that work is being done.

What do you think?

joe

On Wed, 13 Feb 2002, RAUBER, JOEL wrote:

Joseph et. al.

Since you brought up Sherwood and Chabay's book, here's something I'd like
to hear opinion of the list regarding.

page 559 paragraph towards the bottom and I quote: they are discussing a
traditional motional emf problem of a conducting rod sliding on rails
immersed in a uniform magnetic field.

"The magnetic force evB is a non-Coulomb force (references to page 220 and
350). The work done by this force in moving an electron from one end of the
bar to the other is FNC L = evBL. . . ."

FNC = non-coulomb force.
evB is magnitude of (e v_vec cross B_vec)

IMO this is a blunder of a statement. magnetic forces of the ev X B variety
do no mechanical work! Do others read this the same way I do? Have more
recent printings changed the wording? I have first edition first printing.

Joel Rauber

-----Original Message-----
From: Joseph Bellina [mailto:jbellina@SAINTMARYS.EDU]
Sent: Wednesday, February 13, 2002 4:04 PM
To: PHYS-L@lists.nau.edu
Subject: Re: Batteries


This is
not original
with me...read Sherwood and Chabay.

I just don't think there is good evidence to support an electron
transfer model.

cheers,

joe




Joseph J. Bellina, Jr. 219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556