"Jim Kelley" wrote in message
...
Dave wrote:

"Art Unwin" wrote in message
...

( I am assuming that skin depthg is not limitless.)

of course it is limitless, it is an exponential function so it never goes
to zero. the so called 'skin depth' is only the point where the current
has dropped to 1/e or about 37% of the surface value, still a significant
current.

The plots at the link Frank provided show current going rather abruptly to
zero - even negative ("contrary"?) in some cases. I wouldn't presume to
know whether it is modeled correctly.

ac6xg

the 'contrary' current makes sense because of 2 different effects. the main
one is the phase delay of propagation through the conductor. the velocity
of propagation of the wave within the wire is MUCH slower than through space
outside the wire. this produces a phase delay such that when you take a
snapshot, as those plots most likely are, you can get opposing currents. if
you were to take a time average or peak value you would get the plain
exponential as predicted by the simple equations that are normally taught.
The other confounding factor on those examples is the discontinuity between
the copper and steel, again the velocity changes across that boundary
shifting the phase in a step.