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Re: AC electricity



At 09:45 AM 1/22/01 -0800, Leigh Palmer wrote:

I'm taking an analytically simple geometry here, an infinite, straight
wire of resistance per unit length r, carrying a DC current i*.

That's not a "circuit". Bizarre things happen in non-circuits.

You may
approach this situation as nearly as you wish in practice, say with wire
wrapped around the Earth's equator, or even more nearly with gedanken
materials.

It's not clear that such an "approach" is well-defined. The answer depends
on the details of the method of "approach". The field of a wire falls off
very slowly (logarithmically) so there are some integrals that are very
slow to converge. You can easily get tripped up by improper "interchange
of limits and integration".

I'm also taking the DC case, so of course the part about
predicting the future is nonsense, but the reification of the energy
flow is the most condemnable nonsense; that's my point.

Again the method and the conclusion are highly questionable. DC is the
limit of infinitely long timescales. But the "simple" geometry has an
infinitely long wire. Which infinity is bigger? How long did it take to
set up the distant part of the fields in the initial conditions?

David is correct in saying the flux does not extend to infinity in the
case of a finite circuit.

Right. I would recommend analyzing finite (!) circuits (!) only.