Re: Current in a wire

[William Beaty <billb@ESKIMO.COM>]

On Wed, 22 Mar 2000, Leigh Palmer wrote:

> At 2:03 PM -0800 3/22/00, John Denker wrote:
>
> > At high frequencies, it travels only near the surface.  Reason:  the
> > current is deflected by its own magnetic field.

Another way to say it: the metal of the wire acts as an electromagnetic
shield, and the external "shell" of the metal wire shields the interior of
the wire from fast-changing signals.  Since changes in current are caused
by EM waves and propagating regions of net surface charge, the changes
begin at the surface and can only work their way inwards over time.

I think there's another way to describe this too: the speed of light
through a metal is very very low, otherwise the changes in current could
propagate inwards much more quickly.  (Is this right?  Or is it more like
a resistor/inductor ladder network, where transient changes in
voltage-current can move along, but we cannot really call them
electromagnetic waves.)


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