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Re: simple magnets question



Here's another thought-experiment which illustrates some of the problems
which arise when thinking about Faraday's Disk.

Suppose a copper ring is moving through a uniform magnetic field. Since
the flux within the ring is unchanging, there should be zero EMF around
the ring, and zero induced current. I think we all agree on this.

However, what do the individual electrons in the copper ring do? Well,
since they are moving through a magnetic field, they should experience a
perpendicular e-field. Depending on how the ring is oriented, this should
drive them to one region of the ring, and as a result, a static charge
separation should appear across the ring. The free electrons would only
move until the e-field caused by their new distribution was balanced by
the e-field created by the ring's uniform motion through the magnetic
field. There is always a zero current around the ring, but the uniform
motion of the ring does have an effect on the individual charges.

To think about:

If the ring was accelerated in a straight line back and forth through
the uniform magnetic field, there would still be zero current around the
ring. However, wouldn't we see an alternating current as the electrons
all rush from one side of the ring to the other? Will a hunk of metal
get hot if we wiggle it in a straight-line motion in a uniform magnetic
field?


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