My understanding of a permanent magnet is that it has the potential to do work. This would seem to me to imply it has a kind of magnetic charge similar to how a battery is charged with energy. Does this imply that that using the magnet to do work will expend this charge causing the magnet to become less magnetized with each use? If not how can this be explained given conservation of energy?

  • $\begingroup$ The work done by a field is by virtue of its position in space (potential energy). The sun doesn't lose mass just because it attacts earth. $\endgroup$ – Sam Jan 20 at 6:01

The reason one does not use permanent magnets alone for electromechanical devises, is because permanent magnets would rapidly lose their magnetization if energy is taken from them. The law of conservation of energy is always at work, and the potential energy turning into kinetic energy will deplete the magnetization of the permanent magnet.

Permanent magnets can be demagnetized on purpose. The answer to this question may help.

  • $\begingroup$ This seems to contradict the answer above. $\endgroup$ – Derek Seabrooke Jan 20 at 16:58
  • $\begingroup$ if you mean niels' answer with the "directly"depends what "directly"means. , consider mine as a clarification and extension. I have given links. $\endgroup$ – anna v Jan 20 at 17:25

The magnet may perform work while attracting another magnet or a piece of iron, but all that work is reversed when you take the two magnets and pry them loose from one another and separate them again. Energy is conserved in this process.

To make a chunk of iron into a permanent magnet requires you to perform work upon it, so as to align most of the magnetic domains in the iron in the same direction. Using the resulting magnet to attract other pieces of iron does not directly destroy the alignment of the magnetic domains within the magnetized chunk of iron (which process also requires work), but there are other processes that can do this- like subjecting the magnetized iron to a rapidly alternating magnetic field, or heating it up above a certain critical temperature whereupon the domain alignments get thermally jiggled into randomness.


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