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Q & A: magnetism and relativity

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Most recent answer: 01/11/2010
Q:
Hi, Is magnetism a relativistic effect? Or is it caused by angular momentum (spin) of electrons? Are these explanations "two sides of the same coin"? I've seen the mental experiment of two parallel cables and I'm almost convinced, but what about ferromagnetic materials? Can this also be explained using the principles of relativity? This thought process is melting my brain!!! It seems to me that a lot of other things can be better understood by getting a firm grasp of this concepts, but I'm having a hard time finding definitive answers...
- Jose (age 21)
Puerto Rico
A:
What excellent questions!
Yes, magnetism is a relativistic effect and it is for the most part caused by electron spins, and these are two sides of the same coin.

I recommend the book by my freshman physics teacher, Ed Purcell, for a beautiful introduction to the connection between magnetism and relativity. It turns out that in order for phenomena to follow the same laws in all reference frames, the electrical force has to be accompanied by a velocity-dependent force, which we call magnetism. The same reasoning applies to other forces, in particular the nuclear forces, but since they were discovered after the relativistic argument was understood, nobody made up special names for their velocity-dependent parts.

We have many other answers on ferromagnetism, so why not check those and get back to us if you still have questions on it.

Mike W.

(published on 01/11/2010)

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