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Spherical Magnet
Name: Mohamad
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Are there any sphere magnets? Could we make a magnet
which its inside is - pole and outside is + pole?
Replies:
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.
Vince Calder
Mohamad-
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
field.
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
self-demagnetization.
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
no keeper,
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
wide direction.
Your sphere is the worst: a finite equivalent to an infinite plane plate.
Jim Swenson
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Update: June 2012
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