Oh, a warning about playing with glass & charge....

If you do decide to play with charges stored on glass plates wear eye
protection because every once in a while the mechanical stress is more than
the glass can take and it will shatter.

One way you can do this is to go to your local video arcade and purchase one
of the glass sheets they use to cover their pinball machines. Then carry
that glass plate by the edge in your hand as you scuff your feet across a
nylon pile carpet (again wear safety glasses). The result about 1 out of 100
times, or if you've got lots of patience and can afford hours to scuff feet
on carpet, is that the glass plate will shatter with a report about
equivalent to a .22. Anyone watching should also wear eye protection as the
shards can go 20ft. or moe. It's best if you do this on a cold dry day.


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At 1:38 PM -0800 11/21/98, Jim Choate wrote:
>If you do decide to play with charges stored on glass plates wear eye
>protection because every once in a while the mechanical stress is more than
>the glass can take and it will shatter.
>

And when you do your "...and then take away one of the copper plates"
experiment, you'll find that force is needed. Force times distance is
energy. The energy to pull one of the plates away equals the 0.5CV^2 energy
no longer stored in the capacitor.

The energy stored is not stored either on the plate or on the insulator. It
is in the electric field.

A free-standing single conductor can of course store a charge. And can of
course have an electric field.

Frankly, Jim, you no doubt have a lot of practical experience building
Tesla coils, Van de Graf generators, whatever.

But you also have what can only be described as "crankish" notions about
how electromagnetism works (pace last week's discussion of charges inside
conductors, a la Gauss), about prime numbers, and so on.

--Tim May

"I swear to tell the truth, the whole truth, just the way the President did."
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