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Re: charged parallel plate capacitor



"Farrell-Gray, Catherine" wrote:

If there were a vacuum between the plates would the charge leak or would the
capacitor be able to hold the charge? Is there such a thing as a capacitor
with a vacuum between the plates?

Ever hear of a vacuum tube?
http://www.mc-h.demon.co.uk/vtheory/vtheory.htm

Any capacitor will fail if it gets too hot and/or
the fields get too strong. But ordinary metal
plates in a vacuum make a very fine capacitor.

It's a simple barrier-penetration problem. An
electron in metal has a lower energy than an
electron in vacuum, by several volts. This is
the work function as we discussed a couple of
weeks ago.
http://www.monmouth.com/~jsd/physics/battery.htm

If you want to pull an electron out of a metal
by brute force, you need a field that will develop
several volts over a distance of a few angstroms;
otherwise the tunneling current _through_ the barrier
is negligible.

Or you can rely on temperature to hop a few of
them _over_ the barrier.