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Re: induction or hysteresis?



I wonder what the heating mechanism might be? A high-permeability
material with no hysterisis wouldn't have hysterisis losses. If the iron
is acting like a transformer core, then using a magnet and a piece of
copper wouldn't work, since a totally-saturated saturated magnet only
provides a static field, but does not act like a ferromagnet for AC
fields. (Maybe ceramic magnets tend not to be very saturated.)

Think of a transformer where the ends of the secondary are simply shorted
together. The induced emf will produce a large current that tries to
oppose the changing external field. With ferromagnets, the external field
is amplified, so the current is also increased. More current = more
"heat".

For a transformer, we think of the coils and the magnets as separate. For
the pans, the transformer (in the form a single turn of the bottom of the
pan) and the magnet are one and the same.

Or think about the "jumping ring" apparatus. If you hold the ring still,
it warms up. If you have an iron core, the force and the heating are both
larger.

Tim Folkerts
FHSU

P.S. It's possible to do "containerless melting" with this technique, and
it's cool to watch. With the right geometry for the "primary" it is
possible to levitate a piece of metal with a low current, melt it in
mid-air with a larger current, cool it with a small current while still
levitating, and then lower the resolidified piece back to the surface.