Poles on Toroidal Magnets?
Most recent answer: 10/22/2007
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, youve represented a toroidal (donut-shaped) magnet. At each head, theres also a tail, so no point is more N-like or S-like. Therefore a toroidal magnet has no poles. Theres 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 dont 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)
(published on 10/22/2007)
Follow-Up #1: donut-shaped magnets
- Razin Shaikh (age 16)
Navsari, Gujarat, India
This is closely related to an old question: . This donut magnet has no poles.
We should slightly correct the old answer. In an ideal donut-shaped (toroidal) magnet, the field outside the donut is zero. In that sense, it doesn't behave like the horseshoe magnet, which can pick things up via the field outside the magnet. The domains (again in this ideal case) join up to form one domain (as they would also do for an ideal horseshoe), but now with the field axis looping around the donut hole in circles.
Here's a site with some nice pictures of the field:
(published on 09/24/2015)