Re: Re charged insulators

[Gary Karshner <karshner@STMARYTX.EDU>]

> Suppose a properly selected plastic insulator is volume-electrified as
> above and allowed to solidify. You will have a permanantely charged object
> with interesting properties. For example, a positive "pith ball" of 0.001 C
> and a negative one ...  And not only for classroom demos. A patentable
> project anyone?
Ludwik,
        You just re-invented the electret! A permanently charged capacitor,
unfortunately it was patented many years ago. They were used in some early
TV sets to generate high voltage, and more recently in electrostatic or
condenser microphones to supply a fixed bias voltage. Sound hitting the
electrified diaphragm of these microphones varies their capacitance causing
charges to flow.

Gary

Gary Karshner

St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU