Re: a question from a student

[inet@intellisys.net (brian whatcott)]

At 02:42 PM 4/7/97 EDT, LUDWIK KOWALSKI wrote:
> ... Why should the 
> neutrality of the source be taken for granted? Why should we assume that
> "what comes in" and "what comes out" of a battery must always be exactly
> equal? An assymetry of several hundreds of nC would not lead to an 
> explosive situation. 
>
> We need something else beside the law of conservation of Q. What is it? 
> Something specific inside each battery? A general law? Gauss's law can be 
> satisfied by unequal charges on the plates, and on the electrodes. Should 
> a desire to find an explanation be supported or should it be suppressed 
> with a comment like "do not ask silly questions"?
>
> By the way, Alex (or anybody else), where can I order supercaps with
> C larger than 1F. I have two students collecting data on deviations from 
> exponentiality in discharging; we want to see if deviations are more
> pronounced when C becomes larger. Several months ago you made us aware 
> that 50F capacitors are now commercially available....

My time for library research is not always  as much as I would want in the 
weekday evenings, or perhaps my motivation for these capacitor questions is 
not as high as it could be.

 Accordingly, I will offer suggestions as to the appropriate answers, without
offering the literature support that I would prefer.

1) I have seen forces of large magnitude computed for charge imbalances of 
small degree in conductors.

2) There was an early interest in the behavior of capacitors wrt  memory after
discharge from a constant voltage. They were showing some recovery.
Kelvin ( I think it was) showed that it was merely necessary to have two
dielectric layers of different permittivity, both of which had some modest 
level of conductivity or leakage, in order to obtain this effect....

3) Distilled water, if it can be maintained in its pristine state, has 
rather desirable values for resistivity and dielectric constant.  This would 
be one avenue to reasonably sized caps - obviously not so large as 
electrolytics can be made.

Regards
brian whatcott <inet@intellisys.net>
Altus OK