Name: Mike S.
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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Update: June 2012