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Name: Mike S.
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 2000-2001

I think I understand the basics of a homopolar generator. A disc is spun in front of a magnet and an electrical current flows in the disc. my question is, Can the disc be attached to the magnet (insulated and glued) and have both spun together and have an electrical current formed on the disc? The reason I ask is that there seems to be conflicting information about it and I cannot seem to find any "reliable" information on it. Thank you.

No, that does not work. You have a question on one of the most subtle parts of physics. A charged particle moving through a stationary magnetic field feels a magnetic force. However, if that field is moving with the particle, though the field may be of the same strength as in the previous case, the particle feels no force!

It can, perhaps, best be explained by realizing that the force is really between the (moving) charged particle producing the field and the (moving) charged particle acted on by the field. The field is a construct which (sometimes) simplifies the thinking about magnetic forces (and sometimes complicates the thinking).

The physics is even more subtle. Two positive charged particles at rest repel each other. If they move at the same speed parallel to each other, there is an attractive magnetic force. Newtonian relativity says that if you run with the moving charges, the physics must be the same. However, that eliminates the magnetic force for the running observer!

In fact, this problem was a main impetus for Lorenz and Einstein to develop the theory of special relativity. If you watch the particles flying by, Einstein says their clocks slow down and they are repelled more slowly, which is another way of saying the magnetic attraction slows their motion apart induced by the electrostatic repulsion.

I hope this is clear. It is NOT simple. Let me know if you'd like me to try again. Best, Dick...

Richard J. Plano

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