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Where are the poles on a torus-shaped magnet? Or is every point on the magnet a pole?
You can picture a piece of a magnet as a small arrow, with the tail
the S pole and the head the N pole. Now if you make a loop of these
arrows, you've represented a toroidal (donut-shaped) magnet. At each
head, there's also a tail, so no point is more N-like or S-like.
Therefore a toroidal magnet has no poles. There's still a magnetic
field inside, but it falls off more quickly outside than does the field
from a magnet with poles. That can be very convenient if you don't want
the magnetic field inside the torus to affect stuff outside, and
vice-versa. Toroidal electromagnets are used to make transformers, and
also used as inductors in electronic circuits.
Mike w (and Tom)
(republished on 07/13/06)
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