Are there any sphere magnets? Could we make a magnet
which its inside is - pole and outside is + pole?
Yes there are spherical magnets, but the poles are not concentric. I do
not think that "inside /outside" geometry is possible. If you search the
term "magnets for sale" or similar term you will find numerous magnets in
all shapes, sizes, and strengths. One note of caution: Some magnets are
very powerful, so keep them away from your computer, cell phone, watches --
electronic devices in general.
A spherical metal shell magnetized N or (+) inside and S or (-) outside:
- could exist, no problem
- could not be "made" while in spherical form
(one would need to magnetize small wedge-shaped pieces end-to-end,
then assemble many into a shell)
- could not be used for anything known while in that form
(field lines go from (+) to (-) through empty space, in most of our uses,
but in a shell there's no way out and no lines in the interior space" zero
I wonder, would the magnetic potential inside be higher or lower than that of
the space outside?
Magnetic potential is usually a vector quantity, hence not very useful,
unlike the understandable scalar quantity of electrostatic potential.
But in this spherical configuration I think there might be a scalar value to
the magnetic potential.
So if you had a bunch of cold,stable magnetic monopole particles that can pass
through solids freely,
they might find this sphere a welcoming container.
Too bad monopoles are figments of scientific imagination so far.
When field lines cannot reach around a permanent magnet
they are pretty much forced to double-back within the magnet material itself.
This is the opposite of using a passive iron "keeper" on the magnet:
it maximizes the stress the magnetization causes, towards partial
Neodymium magnets would not care much,
but Alnico might well be weakened by keeping in that configuration.
However it is not much worse than a large, wide magnet plate alone in air with
which is a very common configuration for Nd magnets but disfavored for Alnico.
Materials which are polarized strongly enough to challenge their coercivity
do much better if magnetized in a long-thin direction instead of a short and
Your sphere is the worst: a finite equivalent to an infinite plane plate.
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Update: June 2012