From where do magnets obtain their "energy"?

03 October 2010

Question

Why don't magnets ever "run out of power" to attract or repel?  Ferromagnets, in particular. I understand why electric current magnets keep working as long as there is a current, but ferromagnets don't use current, so why do they keep working? Isn't this a contradiction to entropy?

Answer

Dave - Okay. In order to create a magnet, you've actually got to put some energy in in the first place, including for a permanent magnet. You've got to align all the atomic magnets inside the piece of iron and rotate them so their individual magnetic fields all add together. That takes some energy to do initially, but once that state is in place, you don't require any more energy to maintain it. It's a bit like saying, "Why does the Earth keep attracting us forever with gravity?" They're just forces which exist forever.

The actual magnetism in a piece of iron or in a permanent magnet is actually caused essentially by electrons orbiting in one direction more than the other, and the electrons are going to keep on orbiting, as far as we know, indefinitely, unless something interrupts them. So the little atomic magnet is going to carry on forever. There's no reason why the magnet shouldn't carry on.

Chris - It's basically not burning off any energy to make the magnetic field, and it's something interacting with the field that actually makes an effect rather than the other way around.

Diana - But why is it then that some magnets get demagnetised over time?

Dave - Okay. The atomic magnets would stay magnetised, but, if you drop them, you can cause them to re-align a bit every time you drop them. Also, if they get very hot, they can get re-aligned as well. So, the atomic magnets are still there, but instead of all pointing the same direction they start to become more and more randomly organised, so the overall field is less and less, and less.

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