I was recently reminded of something that's been bugging me. When an
electron moves at right angles to a uniform b-field in a vacuum, it
follows a circular path. What happens if we turn this situation
inside-out? Suppose we place an electron in the field of a thin
disk-shaped permanent magnet which has poles on the opposite faces of the
disk, and then we briefly rotate the disk on axis. Assume that everything
is stationary at the beginning, then reach out and give the disk-magnet a
twist. What does the electron do?
Or if the sudden change in motion is a problem, then instead what will
happen if an electron approaches a disk-magnet which is already spinning?