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Re: Chabay/Sherwood

I believe the book may be written to take into account
the probable viewpoint(s) of a student new to the
topic and to recognize the likely preconceptions he or
she is likely to have. For example, twists and turns
on a path force you to move more slowly than if it
were straight. I think it's very understandable that
many students would expect steady-state current in
wires to be similarly affected. Etc, etc. John Barrere
--- Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>
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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