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Re: Chabay/Sherwood



I'm always interested in such discussions. I'm not familiar with
"Electric & Magnetic Interactions" of Chabay and Sherwood however.



At 9:45 AM -0500 on 2/15/02, Ludwik Kowalski wrote
Pedagogy aside, "Electric & Magnetic Interactions" of Chabay
and Sherwood is conceptually very unusual textbook. The idea
of static charges on the surfaces of wires with currents is worth
discussing. Was this discussed on Phys-L before? If so then
by whom and under what subject name?

I keep having questions as I read. For example, "is it OK to
assume that surface charges create electric fields both inside
and outside the wires when the current is flowing?" But then
I realize that not everybody has this textbook, or wants to
discuss surface charges as this time.

Therefore, UNLESS AT LEAST TWO OR THREE OTHERS
EXPRESS INTEREST, perhaps those who want to help me
should reply in private. <kowalskil@mail.montclair.edu>

Ludwik Kowalski wrote:

I started reading "Electric & Magnetic Interactions" of Chabay
and Sherwood. I need some help.

1) ON PAGE 208 (Section 6.2.1) THEY SAY:

Now consider a circuit consisting of our mechanical "battery"
[Van de Graaff] and a nichrome wire that has some twists and
turns in it. You know from your own experiments that such
twists and turns do not seem to affect the amount of steady-
state current, which seems odd.

WHY SHOULD IT SEEM ODD?

2) REFERRING TO THE FIGURE ON PAGE 208
(PAGE 240 SHOWS IT AGAIN WITH MORE DETAILS)
THEY WRITE:

Good greef! We've got the electron current running upstream
through part of the wire!

I SUPPOSE THAT FOR ELECTRONS THE WORD
"UPSTEAM" MEANS "IN THE DIRECTION OF E."
WHICH "PART OF THE WIRE" IS IT?

3) REFERRING TO THE "LEFT BEND" ON THE SAME
FIGURE THEY WRITE:

Take a look at the left bend of the wire. If the only charges
were on the plates ["battery" terminals ?] electron current
would flow toward the bend from both neighboring sections.

I HAVE NO IDEA WHY WOULD ELECTRONS CONVERGE
ON THE LEFT BEND FROM BOTH SIDES DUE TO THE
CHARGES ON THE PLATES. I WOULD EXPECT ELECTRONS
TO ENTER THE LEFT BEND FROM ABOVE AND LEAVE IT
FROM BELOW. CHARGES ON THE PLATES CREATE A
> FIELD "PUSHING ELECTRONS". WHAT AM I MISSING
> IN THEIR EXPLANATIONS?
> Ludwik Kowalskil

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