Re: conserving Q/Faraday

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

Bob Schimanda wrote:

> Something seems to be happening when you separate the capacitor
> components. Can this separation be done inside the Faraday cup?
> Perhaps the entire process: charging, discharging and separation could

> be done inside the Faraday cup, giving a constant monitoring of the
net
> charge of the system to actually see when it occurs.

Yes, this is definitely worth trying. Thanks. And here is something
else.

The Faraday cup tells us nothing about the surface distribution of
charges
on an electrified sheet. Last evening we tried to visualize charges in
the
following way. We took toner dust, used in Xerox and laser printing
machines, put it into a big jar and shook the closed jar to create a
cloud
of dust inside. Then we opened the jar, waited a moment or two, and
inserted an electrified Lexan sheet into it for about a second,
vertically.
An interesting pattern of shaded gray was formed; probably the image
of charge distributions.

We see small circles, we see ridges. A pattern on one side of the sheet
is
exactly the same as the pattern on the other side. The shapes of lines,
and
degrees of local darkness, are nearly the same, as far as one can say by

looking at the two "fingerprints", that is at what appears on two pieces
of
white paper after the sheet is squeezed between them. The distributions
of charges are not uniform. Is it due to some non-uniformity in the
dielectric material? Or to the invisible structures on aluminum plates?
Or is it a randomly formed pattern to be different each time?  We have
to explore.

The goal was to see if the procedure can be used to visualize our net
charges. We are probably at the level at which xerography was 60 years
ago. A single sheet of Lexan (about 0.3 mm) was kept for ten minutes
under 5000 volts before being inserted into the dust cloud. The near
identity of patterns on both sides seems to indicate that these are
positive
and negative bound charges. But not necessarily. Suppose there is an
island of net charges somewhere inside. Why can't it affect both sides
in the same way?

Will the imaging work at lower d.o.ps? Or on other dielectric materials?

Can it be used on sheets electrified near an electrostatic machine?
Looks
like another good project for students to investigate. Try it, you will
like it. And do not forget to share your observations.
Ludwik Kowalski