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# Why is a magnetic field of a permanent magnet not considered energy?

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1 law cant create energy. ok but you can give energy to a ferromagnetic and magnetize it. then magnetize as many ferromagnetic material as you want, and not diminish the magnetic field of the 1st one you had. I dont understand how no loss and how that is not considered braking the 1st rule

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A magnetic field does contain magnetic (potential) energy.

Quoting from Wikipedia: The energy per unit volume in a region of space of permeability uo containing magnetic field B  is:

U = ½ B2/uo

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On 10/11/2020 at 10:34 AM, Vipera2006 said:

1 law cant create energy. ok but you can give energy to a ferromagnetic and magnetize it. then magnetize as many ferromagnetic material as you want, and not diminish the magnetic field of the 1st one you had. I dont understand how no loss and how that is not considered braking the 1st rule

Actually, I think there would be loss in the first one.

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10 hours ago, montgomery said:

Actually, I think there would be loss in the first one.

I agree. So-called permanent magnets do not have 100% retention of their magnetic fields, although they can retain their fields for a very long time. One estimate I have seen is that the permanent magnet will lose only 1% of its field strength in 100 years if left undisturbed on a shelf.

However, using the magnet to magnetize other objects is not quite leaving it undisturbed. That being said, even if there were no loss in the primary magnet, that would still not violate conservation of energy. The usual explanation for the source of energy, in magnetizing a secondary magnet using a permanent magnet, is the mechanical work done in passing the object through the magnetic field. But I question whether the magnetic energy acquired by the secondary magnet comes entirely from the mechanical work or from some combination of mechanical work plus some of the potential magnetic energy lost by the primary magnet.

It seems logical to me that at least some small part of the energy gained by the secondary magnet comes at the expense of some tiny lose in the strength of the primary magnet’s field strength. We know that mechanical shock or vibrations as well as heat can destroy some of the atom electron alignment in the permanent magnet, causing loss of field strength. But the loss of field strength caused by magnetizing a secondary magnet, if any, may be so tiny that it is simply ignored for practical purposes.

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