Re: EM Induction - A conceptual question

["Carl E. Mungan" <mungan@USNA.EDU>]

Chuck wrote:

> I'm not familiar with this symmetry argument for 1/2 strength at the ends.
> Would you elucidate it please?

Consider an infinitely long solenoid. The field at some interior
point is B (=u0*n*I as usual). Say the point is on the axis. Slice
the solenoid in half at that point. By symmetry, both the left
semi-infinite half and the right semi-infinite half must make equal
contributions to B. Hence, the field on the axis at the end of a
semi-infinite tightly-wound solenoid is B/2.

Note that this argument only gives the longitudinal component of B if
you go off-axis because the diverging field lines (as the field
"sprays out" near the end) imply there is also a radial component.
Carl
--
Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
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