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Re: ORIGINAL simple magnets question

On Mon, 28 Jun 1999, Clarence Bennett wrote:

Bill,

I have hot-glued a round fridge magnet, well centered, to a plastic rod.

I hope to chuck it in a reversible drill and clamp the drill near a Crooks
tube, (if they haven't all been confiscated), or the Welsch transparent
oscilloscope.

Would you care to predict whether the beam deflection will differ according
to the rate and direction of spin?
Or is this not somewhat equivalent to your original proposal?

That's the right experiment in theory. However, I think the "motional
e-field" will be far too small to measurably deflect the beam. I've heard
that the electrons in a typical oscilloscope are moving at a good fraction
of light speed. The motions of a spinning fridge magnet will seem
insignificant from their reference frame. Or, another way to look at it
is that the strength of the "motional e-field" is going to be far below a
volt/cm even at the surface of the magnet, to say nothing of several cm
away, so the field is far too weak to cause noticable deflection of the
beam.

A second big problem: if we put an e-field outside an oscilloscope tube,
the electron beam will not be deflected. I think it was Thompson who
figured out the trick of putting the electrodes inside the tube. The tube
itself behaves as a shield because the vacuum is full of mobile charges.
The spinning magnet would have to be in a vacuum chamber, and spinning so
fast that the rim of the magnet is moving at a fraction of c. Either
that, or somehow slow down the electrons so they are going at a few
meter/second. That's a very low temperature in terms of thermal velocity.




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