Re: how many volts ?

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

On March 25, 1997 Bob Sciamnda wrote:
> ............. The relation can obviously be turned into:
>
> |Q| = C*|V| , where the C_i,j are the "coefficients of capacitance".
                How can this be applied to our problem?

> These relations have gone out of fashion in most recent textbooks (only 
> the "capacitor" of two equally and oppositely charged conductors is 
> typically now treated). 

Finding a distribution of static charges is not trivial. Our introductory
texts simply impose distributions, nearly always uniform, and derive their
properties. In the case of very large metallic plates, facing each other, we
accept the uniform distribution and calculate E or C (adding that the fringe 
effect is negligible). As you know, the problem of two metallic spheres,
with a short gap between them, for example, is much more complicated.

I will try to demonstrate numerically (withot using calculus, as I must do
in what I teach) that the charge distribution on a single metallic disk is 
not uniform. This is usually accepted on the intuitive basis; "charges of 
the same kind mutually repel and try to stay away from each others".
                                           Ludwik Kowalski