Re: simple magnets question

[William Beaty <billb@ESKIMO.COM>]

On Fri, 25 Jun 1999, Leigh Palmer wrote:

> Note that the "ring magnet" described above is not magnetized
> like Bill's spinning disk; it is more like the spinning
> horseshoe magnet someone else described. A similar "ring
> magnet" is to be found in a toy called "Top Mystery". The
> direction of magnetization is in the plane of the ring; the
> gross geometry is misleading. I expect you will find that
> your ring magnet is also polarized in a surprising manner.

If a spinning Faraday-disk magnet is held near a metal plate, there should
be a zero current (but perhaps there will be a brief, tiny radial current
when the plate is first brought close to the magnet.)

Separate topic: suppose that whenever we stop and start the rotation of an
axially-magnetized disk-magnet, it does produce a tiny radial current in a
nearby copper plate.  That heats the plate.  That takes work.  The magnet
should experience a small torque.  What equations govern such a thing????


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