Re: electrostatic shielding

[Leigh Palmer <palmer@SFU.CA>]

> 1) Let me add the obvious; the value of G changes
> gradually from 1/(2*Pi) to 1/(4*Pi*) when the distance
> is increasing. The first value is for a very large flat
> metallic disk, where sigma=Q/(2*Pi*R^2). The second
> is for a point charge (the disk seen from "infinity").

That is certainly not obvious to me. The value of G cannot be
as large as 1/(2*pi) because the charge on the disk will flow
preferentially to the edge; the surface charge density at the
center must be less than Q/(2*pi)R^2

> 2) The formula for S(r) is intuitively acceptable but
> how do you justify it formally, Leigh? There may be
> many even functions with a minimum at r=0.

This is a perfectly general function having the correct
symmetry property.

> The
> sharpness of the disk edges will probably play a
> very significant role in the S(r) distribution.

I think that is not the case if the disc is thin (thickness t
of disc is much less than the radius R).

Leigh