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Q & A: is there current in a bar magnet?

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Most recent answer: 05/02/2015
Q:
Is there a current in a bar magnet, and if not, where does the magnetic field of that bar magnet come from?
- alex (age 15)
Manchester MA USA
A:

Almost all the magnetism in a typical bar magnet does not come from currents. It comes from the intrinsic spin magnetism of electrons. Electrons have that spin magnetism even when they aren't going anywhere.

 You can actually measure how much of the magnetism is spin vs. how much is from currents ("orbital")  by measuring the amount of magnetism per amount of angular momentum. The ratio for spin magnetism is twice a big as the ratio for orbital magnetism. The first version of this experiment was done by Einstein and deHaas, the only experiment that Einstein ever directly participated in.

Mike W.


(published on 05/02/2015)

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