ORIGINAL simple magnets question

[William Beaty <billb@ESKIMO.COM>]

On Fri, 25 Jun 1999, Michael Edmiston wrote:

> I don't want to put words in William Beaty's mouth (or thoughts in his
> mind) but I would guess that his original problem

I still think we are having communication problems.  My "original problem"
was my prediction that a spinning disk-magnet would affect the trajectory
of an electron differently than a non-spinning magnet, even if the b-field
is not being varied by nonuniformities in the spinning magnet.  Is this
wrong?  If so, then I still haven't figured out why it should be wrong.
And I don't understand why a small portion of the b-field above the edge
of a very large disk-magnet should behave differently than the b-field
above one of the pole-pieces of a cyclotron. Spin the disk-magnet, and
points on the EDGE of the disk will move approximately in a straight line.
Move the cyclotron, and the pole pieces move in a straight line.  If the
observer travels along with the edge of the spinning disk, or travels
along with the moving cyclotron, that observer would see no local e-field
in either case, correct?  (Assume the disk is very large, so that
non-inertial effects near the rim can be ignored.  Or can they?)

> Regardless of whether some of us view this as simple, or intuitive (or
> both), I infer it was not intuitive to Bill.

It never seemed intuitive, but it all seems very familiar and sensible,
since I know that cyclotrons have a uniform field, yet they still can
deflect an electron in relative motion.  Everyone please read my messages
carefully.  Others here said that electrons can only be deflected if the
b-field is non-uniform.  I am arguing the opposite: that an electron
*will* be deflected if it moves relative to a cyclotron, but *won't* be
deflected if it travels along with a moving cyclotron.  If people want to
carefully prove to me that my assertions are correct, then I must conclude
that they didn't read my message closely, and they assumed that I was
saying the opposite of what I actually said.  If I say 2 plus 2 equals 4,
and everyone wants to patiently explain to me that 2+2 actually equals 4,
then I am confused!

I say:

  1. If an electron moves relative to a cyclotron's poles, it will
     experience a *net* transverse force.

  2. If an electron DOESN'T move relative to a cyclotron's poles, if the
     electron and the cyclotron fly past the observer together, then
     the electron WON'T experience a *net* transverse force.

These above two are my initial assumptions.  My arguement is that:

  3. If an electron is adjacent to the rim of a very large disk-magnet,
     and if the magnet is spinning on axis, and if the electron is NOT
     MOVING relative to the rim (the electron is momentarily following the
     rim as the rim goes along), then, in the frame of the electron, the
     electron WON'T experience a large e-field.

  4. If an electron is adjacent to the rim of a disk-magnet, and if the
     magnet is spinning on axis, and if the electron is MOVING relative to
     the rim (it is NOT following the rim as the rim goes along), then the
     electron WILL see a large e-field and experience a transverse force.

  5. As far as electrons are concerened, a spinning disk-magnet seems to
     be surrounded with a large e-field which is directed radially across
     the face of the disk, and a non-spinning disk-magnet apparantly
     doesn't have this field.  This field is very weird: sometimes the
     "lines of flux" end in space where no charges exist.

Are 3, 4 and 5 blatently wrong?  If so, why?  Why are they so different
than the situations in 1 and 2?

I've always been imagining that the disk-magnet is very large, that the
electron is near the rim, and therefor any centrifugal effects can be
neglected, but perhaps this is not a good tactic.  General Relativity
might rule the electrodynamics of a spinning magnet, and I'm nearly
clueless about such topics.


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