Re: charged parallel plate capacitor

[Bob Sciamanda <trebor@VELOCITY.NET>]

Sorry, I guess I approximated air as "vacuum" in this question.  Mea
Culpa!

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Bernard Cleyet" <anngeorg@PACBELL.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, February 27, 2002 5:51 PM
Subject: Re: charged parallel plate capacitor


> I've never heard of a vacuum capacitor for a receiver; they're not
> inexpensive.
>
> bc  Who built his first "crystal set" in ca. 1946.
>
> P.s. Still not that uncommon (square law variable caps.), but mostly
replaced
> by varactor diodes, if not by digitally synthesized local oscillators.
>
> Bob Sciamanda wrote:
>
> > > Is there such a thing as a capacitor
> > > with a vacuum between the plates?
> >
> > Not just in transmitters!
> > I'm sure we are not all so young that no one remembers the variable
air
> > capacitor which was commonly used to tune consumer radios in ancient
days
> > (perhaps even as late as the fifties?  :)  One can still find them in
some
> > crystal radio kits for children.
> >
> > Bob Sciamanda (W3NLV)
> > Physics, Edinboro Univ of PA (em)
> > trebor@velocity.net
> > http://www.velocity.net/~trebor