Re: Disectable Capacitor

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

I think that any simple device which demonstrates something
unusual has a pedagogical value. But a teacher must know
how to present it to promote thinking and learning.

Experimenting with dissectible capacitors (already described
here) convinced me that a simple textbook model is an enormous
oversimplification of what really happens. As pointed out by
others, the so-called "Volta's electrophorus" effect plays an
important role when electrodes are separated from an electrified
dielectric. The outcome irreproducibilities are probably due to
strong influence of local initial conditions (very difficult to
control in real experiments). I wish independend data could
be collected to confirm that a dissectible capacitor is a chaotic
device. Otherwise I must blaim my unabilities to control the
beast. See the P.S. note below.


Ludwik Kowalski

John P Lewis wrote:

> The owner's manual suggests that the CHARGE is stored in the dielectric
> between the conductors but I don't understand how this could be.

And BenJamin Franklin, in 1748, wanted to determine whether the seat of
electric "power" of a Leyden jar was in the metallic coating or on the glass.
And he constructed the first dissectible capacitor to answer this question.
It was a glass plate between two smaller plates of lead. He charged the
capacitor from the electrostatic machine, discharged it, removed the lead
plates and examined the glass for the presence of electrization. He found
that the plate was strongly electrized, and that, if it was once again placed
between the lead plates, a strong spark could be extracted from the lead
plates while shorting them with a conductor. .....

(From "Electrets" by O. Jefimenko and D. Walker, The Physics Teacher,
December 1980, pages 651 to 659).