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Re: FUN: high-speed electrostatic air-threads



Bill Beatty wrote:

Then I'm confused about the origins of pinch effect. Take an
electron beam in a vacuum for example. You're essentially saying
that there is some value of current which, if exceeded, leads the
electrons to ATTRACT? I don't understand how this could occur.

You always have the electrostatic repulsion. However, there is also
a magnetic force (from the v x B term in the Lorentz force), which is
inward on the column. The B is the B produced by the current column.
The v is the velocity of the moving charges.

For large currents, this magnetic force can be very important. In
any case, a steady-state diameter of the current column will be
achieved when you have a balance between radially inward forces and
radially outward forces.

I hope this helps,

Regards,
Steven




Steven T. Ratliff
Associate Professor of Physics
Northwestern College
3003 Snelling Av. N.
Saint Paul, MN 55113-1598

Internet: stratliff@nwc.edu (or str@nwc.edu)