Keith Nagel wrote:
Hi Stephen,
I learned this out of a relativity textbook so my view of E&M is a
little cockeyed, I'm afraid, but I don't recall anything about
violations of CoE...
Its tempting to bring out the big guns, but lets start with
something most of the people on this list can intuitively
understand. If the amperian model is true, then it implies
a continous flow of current in the ferromagnetic material.
How does this happen outside of a superconductor? How
does that electron keep spinning on itself to generate
the field without any dissipation?
Dissipation? Hmmm...
I can't give a proper quantum-mechanical answer to what's going on
inside a "domain" in the iron (where a single "domain" is a tiny piece
of an iron crystal which acts as a permanent magnet), but in really
simple terms my understanding is that it is indeed a first cousin to a
superconductor. It's just a very _limited_ superconductor: Each
magnetic domain in the iron comes "from the factory" equiped with a
permanent current loop.
Absent quantum mechanics, we could think of the iron atoms as having
electrons "orbiting" around them. If we did that, and if we could get
the orbits to line up in parallel planes, then voila, we would have a
magnet -- the currents in the interior of the domain would cancel (in
their effects) and the result would be as though there were a single
current running around the outer surface.
There's nothing inherently contradictory here. Unless there's some
resistance present, which would cause the electrons to slow and
eventually fall into the nuclei :-), such a magnet should be "permanent"
as long as the orbits stay lined up.
Now, obviously the "orbit" model is incorrect. But it's QM that says
it's wrong, and presumably somewhere buried in QM there's also an
explanation of how the iron simulates current loops. Regardless,
though, there's no violation of CoE, unless one cares to go back to
Aristotle and say that objects subjected to no external force must come
to a halt.
