Re: Question 07/02 CURRENT IN A WIRE

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

At 11:10 -0500 11/19/02, Bob Sciamanda wrote:
> The laboratory observer sees moving charges which interact via magnetic
> forces, even though their relative velocity is zero.
They interact with each other via magnetic forces? How is this
possible? My understanding of this is that the only reason we see a
magnetic field around a moving charge is that it is moving *relative
to us.* The moving charges in a wire feel a magnetic field because
they see the opposite charges moving relative to them. In a plasma,
there is motion between the opposite charged particles (IIRC a plasma
is only a "plasma" if it is at least approximately neutrally charged,
with approximately equal numbers of both charges roughly uniformly
distributed throughout the region), so there would be a "pinch" due
to the presence of relatively moving opposite charges to create the
magnetic field. But in otherwise empty space, a beam of charged
particles will not sense a magnetic field due to the presence of
other charges in the beam, since there is (very little) relative
motion between them, and hence no pinch effect, only the defocusing
of the beam due to the mutual repulsion between the moving charges.

Am I missing something here?

Hugh
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Hugh Haskell
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