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Re: simple magnets question



On Thu, 24 Jun 1999, John Denker wrote:

Accordingly, we can rephrase the question: imagine that in the lab from an
electron is moving through a magnetic field. At any given point, it feels
a force transverse to its motion. So the question is, what happens in some
other reference frame, such as one comoving with the electron?

Answer: The electron sees an electric field. You can easily calculate the
details of this field by Lorentz transforming the electromagnetic field
tensor from the one frame to the other.

And getting back to the original "simple question"...

If a stationary electron is near the rim of a spinning disk-magnet, then
in the frame of a tiny observer who is riding along with the rim of the
disk-magnet, the electron is moving past a stationary magnet and hence the
electron feels a transverse force. And in the frame of the electron, the
field near the rim of the moving disk-magnet contains an e-field, and
hence the electron again feels a force. Correct?

And this brings us back to my original question: if a disk-magnet is made
to spin on axis, will clouds of nearby electrons feel an e-field which
either attracts them to the rim of the disk, or repels them from it,
depending on the direction of rotation?

Sketch the b-field of a disk-magnet. If the magnet rotates, it should
create an e-field which is radial at the surface of the disk. Farther
from the disk, this e-field points away from a line drawn through the axis
of the disk. It also points towards the rim of the disk, as if the rim
was charged.



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