Re: simple magnets question

[William Beaty <billb@ESKIMO.COM>]

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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