# Rotating Magnet

#### pmb

[SOLVED] Rotating Magnet

I had forgotten about a web page I made several months ago. It's regarding a rotating magnet. There are some cool physics in this page so take a look

www.geocities.com/physics_world/em/rotating_magnet.htm

Back in the early 60's Edward Purcell came out with an idea of how to look at the relativity of electric fields in terms of charge densities. It's not a widely know fact but under some circumstances you can have a zero charge density in one frame of referance and a non-zero charge density in another. If you want to go into the excrutiaing detail the see also

"Magnetism, Radiaton, and Relativity," Daniel V. Schroeder, Weber
State University --physics.weber.edu/schroeder/mrr/MRRnotes.pdf

Pete

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#### Tyger

An interesting page you have there.

I found out about the charge density variation when I was trying to understand superconductivity. It led to a model I call "big wave, little wave" where the big wave is the charge variation across the loop when it is turning and the little waves are the variations which couple the electron pairs to the vibrations of the crystal lattice.

#### pmb

Re: An interesting page you have there.

Originally posted by Tyger
I found out about the charge density variation when I was trying to understand superconductivity. It led to a model I call "big wave, little wave" where the big wave is the charge variation across the loop when it is turning and the little waves are the variations which couple the electron pairs to the vibrations of the crystal lattice.
If you're interested in the details see the Feynman lectures. If youd don't have them then I put the relevant section online

http://www.geocities.com/physics_world/feynman-1.jpg
http://www.geocities.com/physics_world/feynman-2.jpg
http://www.geocities.com/physics_world/feynman-3.jpg
http://www.geocities.com/physics_world/feynman-4.jpg
http://www.geocities.com/physics_world/feynman-5.jpg
http://www.geocities.com/physics_world/feynman-6.jpg

Pete

#### Tyger

I've got the Feynman Lectures

and would highly reccomend them to anyone who's serious about learning Physics. And they're a joy to read and study, he makes the ideas come alive. And the "big wave" idea came right out of Feynman, but I added the little waves to understand the Cooper Pair couplings in SC.

In a somewhat related question, I've always wondered about the legitimacy of treating charge density on the same footing as charge in QFT. Is it realy rigorous?

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