Re: Capacitor problem, a new question

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

Once again a message I posted did not come back to me. And two days ago
I got a message with a wrong header. It was sent to me by somebody who 
has nothing to do with phys-L but the header was saying it is from phys-L.
I also noticed that occasionally corrections made by phys-L authors do not 
correspond to messages I received. Nothing is perfect .... In any case let 
me reposte the file. I appologize to those who might have received it last 
night; a comment on "educated guessing" was referring to what is below.
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Here is a quote from today's statement:

> ... Ludwik's modification is certainly easily explained in terms of a time 
> evolving system as well. He should lose those gratuitous caveats about 
> fringing, however. Fringing exists; it can't be ignored *a priori*. It 
> must be shown to be ignorable in any particular instance in which that 
> assumption is made.

OK, replace the "no fringe effect" by "a situation in which the areas of 
plates are very large in comparison with the distance between them". 

It is certainly not easy for me to answer the new question in a quantitative 
way. I do not know how to calculate the fraction of the LOST electrostatic 
energy which becomes heat (rather than e.m. waves) when the rate of expansion 
is given. I visualize expanding plates as sliding recangles, controled by 
thin nylon strings and rods. Here is an example of a particular instance.

t=0        --->  Plate areas are  5 m^2,   d=1 mm,   |Q1|=|Q2|=10 microC
t=1/10 s   --->  Plate areas are 10 m^2,   d=1 mm,   |Q1|=|Q2|=10 microC

These assumptions imply that V1=226 volts while V2=113 volts. Thus 565 
micro-joules of electostatic energy is lost in one tenth of a second. How 
many micro-joules of e.m. waves is emitted? My intuition tells me it is 
much less than one percent (nearly all becomes heat), but this is only a 
guess.
  ...................................................................
  : Gedanken-ing is not enough; physics is an experimental science! :
  :    Inspired by thinking about phys-L messages on capacitors     :
  :                         Ludwik Kowalski                         :
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kowalskiL@alpha.montclair.edu   http://www.csam.montclair.edu/~kowalski
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