Re: Question 07/02 CURRENT IN A WIRE

[Michael Burns-Kaurin <mburns-k@SPELMAN.EDU>]

Looking at the situation of two parallel charged beams in the lab frame
(the particles are moving):
we would see a magnetic attraction between the beams, but we would also see
electrostatic repulsion.  Both will depend on the charge density of the
beams and on the inverse of the distance between them, but the magnetic
attraction will be smaller by a factor of (v/c)^2, if I did the math right.
So, the lab frame sees a net repulsion.

In the particle frame:
There is only an electrostatic repulsion.  It will have a magnitude
depending on the charge density in this frame, which is less than the
charge density in the lab frame (length contraction).  Again, net
repulsion.

Michael Burns-Kaurin
Spelman College





                      Hugh Haskell
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At 20:52 +0100 11/19/02, Mark Sylvester wrote:
> But Hugh, just last week I was demonstrating to my class the mutual
> attraction of two conductors carrying parallel currents!
No problem there. The magnetic fields are real, and there is plenty
of relative motion to account for it. But imagine two beams of
identically charged particles in a vacuum, traveling parallel to each
other (and in the same direction) and with the same velocity. Other
than some random thermal motion which should cancel out, there is no
relative motion of the charges in one beam with respect to the
charges in the other beam, so can there be a magnetic interaction
between these beams? I can't see how, but I am open to arguments that
refute my claim.

Hugh
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Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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This posting is the position of the writer, not that of SUNY-BSC, NAU or
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This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.