Re: charged insulators

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

> Date: Tue, 07 Jul 1998 19:13:30 -0500
> From: brian whatcott <inet@intellisys.net>
> Subject: Re: Re charged insulators
>
> Such a device is called an electret microphone. (Similar at least - 
> the electret material is simply subjected to a high electric field 
> before solidification)

Many many years I ago tried (just once) to allow parafin to solidify in an 
electric field of about 500 V/cm. No measurable dipole moment was generated. 
Probably because the experiment was not well designed or parafin was not 
pure, or the E field not strong enough, or who knows what.

Anyhow, as pointed out by John Gasineau, a permanant dipole moment is not
the same thing as permanant electric charge (uniform distribution within
the volume). An electret is electrically neutral while the suggested 
material would have a net + or - charge.

Do you know if electrets were cut by somebody to produce net + and - 
"pith balls" for classroom demonstrations of Coulomb's law? Or for any
other purpose. My guess is that this is not possible at the macroscopic
level. The conceptual model of an electret (from the days of playing with 
parafin) is a bunch of more or less parallel strings of short molecular 
dipoles. Each molecular layer is electrically neutral, like in a 
capacitor.
                                                     Ludwik Kowalski