Re: All that glisters is not gold

[William Beaty <billb@ESKIMO.COM>]

On Wed, 10 Feb 1999, paul o johnson wrote:

> Brian (one of them) stated his opinion that "the energy does not go down the
> wire but through the space not the wire". I've always thought that the energy
> is in the field and the field is in the wire. It's what gives the electrons
> their drift velocity.

I'm not entirely certain that I've got this right, but inside the wire
isn't the E x B energy flow directed INTO the wire?  The b-field is
circles about the wire center.  The e-field is directed along the wire.
The poynting vector field points inwards.  I assumed that this was
identical to a model for a resistor being heated.  If the wire was a
perfect conductor, there would be no e-field inside it, and hence no E x B
energy flow pointing inwards.

In the space outside the wire, the e-field is almost perpendicular to the
metal, and the b-field is still in circles.  This gives a poynting vector
field which runs along the wire, from source to load (with a little bit of
it diving diagonally into the wire in order to supply that resistive
heating.)

However, I vaguely recall encountering papers that point out paradoxes in
the location of the energy of electric circuits, so I'm not confident that
the poynting vector field really gives an absolute location for the path
of EM energy flow.  Still, I find it satisfying to imagine that the
electrical energy is like an invisible sausage-shaped "stuff" that rushes
along in the space surrounding the wires, moving nearly at c, at the same
time that the charges in the copper are sitting in place and vibrating at
60Hz.  Sort of like sound waves flowing down a tube, while the air sits
still and vibrates.  Very odd sound waves though, where the propagating
energy is everywhere EXCEPT in the moving air.


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