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Name: Mohamad
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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.

Vince Calder


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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