wrote:
Bill Hobba wrote:

"Tareq" wrote in message
groups.com...

There is a flaw in this page:
http://galileo.phys.virginia.edu/cla...el_el_mag.html

He assumed the wire to be neutral when negative charges were travelling
inside it. While it was more safe to assume that the wire is neutral
when it carries no current , this is what we are sure of. Accepting
that, we will find that the wire will carry a net negative charge when
negative charges are moving due to length contraction and the increase
of the density of negative charges.

Not quite true. Even if a wire has moving negative charges (by moving it is
meant relative to the wire) one can still find a frame where the positive
charges of the nuclei move at the same speed but in the opposite direction


I believe I u once said u tried for a bachelor in electricity (or
electronics)?

If so u would know protons(positive charges) do not move in a wire.

But the wire can move. What didn't you get about "find a frame of
reference where the positive charges of the nuclei move....?"



Only one terminal end has more electrons than the other end, and that
only electrons move and so called "holes" move in the opposite
direction in a wire.

I disagree with that concept, but then that's another argument altogether.



to the negative charges - in which case length contraction is symmetrical so
the wire is still neutral. In such discussions that is what is usually
meant by a neutral charge carrying wire.


no such thing, in terms of electricity and wires.

There is indeed no such a thing. Neutrality of a charge carrying wire is
frame dependent.
A wire with an excess charge in lab frame may very will be neutral wrt
some other frame. Bill's definition seems to include both charged and
uncharged wires, making it a bit redundant. "A wire is a nuetral wire",
IOW.


(in fact I thing I read that electrons can actually become MAGNETICALY
(NOT ELECTRICLY) attracted to each other if they are traveling in two
uninsulated neighboring wires but in opposite direction

You meant "same direction."

(although the
force of their electrical charge might cause a NET repulsion instead of
an attraction...or maybe not if the charges are considered neutral in
their travel).

Nevertheless it's simply not so. A magnetic field, in the classical
context, requires a counter flow of positive and negative charges. A
monopolar beam does not produce a classical magnetic field. This also
follows from Purcell's treatment. In his treatment two comoving point
charges of like sign will experience only the electrostatic repulsion
due to their electrostatic fields. When these charges are drifting
along within conductors then the attractive force that arises is due to
the motion of the electrons wrt the protons in the conductors. In this
my theory agrees with his, but only for test charges. For individual
electrons we must disagree; in my model comoving electrons would exert
no force upon each other of any sort or magnitude. Test charges differ
from individual electrons in that the former are composed of very many
electrons that are all in motion wrt each other on the microscopic
level. These cannot therefore actually comove with each other any frame,
while individual electrons can. Cooper pairs are one example. A coherent
electron beam is another.

Richard Perry



This will result in a net force on
a charge at rest outside the wire of the same order of magnitude as
magnetic forces !!!