The E field on the axis of a uniformly charged disk is given by
E = (2k*pi*sigma)(1-[1+(R/x)^2]^-0.5) (Tipler 4e, p694)
where R is the radius of the disk. Taking the limit as the ratio R/x
approaches infinity gives the field for an infinite uniformly charged disk.
This field is given by
E = 2k*pi*sigma
A plot of E versus x for second equation (infinite disk) is a straight line
with zero slope. However, a plot of E versus x for the first equation
(finite disk) gives a curve whose slope does not appear to approach zero for
x << R. My question is, why not? It seems to me it should.
If someone can shed some light on this I would appreciate it.
Gene
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* Eugene P. Mosca *
* 301 Constitution Blvd. *
* Kutztown, PA 19530 *
* (610) 683-3597 home *
* emosca@ptd.net *
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