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Re: Ions



Last night Crawford Maccallum wrote:

I remember years ago at Sandia Labs folks would expose small slabs of
clear plastic (maybe 15cmx15cmx1cm?) to the Van de Graaf beam. The
slabs could be stored for a long time and then when struck with a sharp
point (hammer and ice-pick) would discharge the trapped electrons
forming handsome dendritic patterns inside the plastic.

What did you mean by "long times"? Hours or weeks?

A beautiful illustration of such pattern ("electrical tree") can be seen on
page
678 of "Physics For Scientists and Engineers" by P. A. Tipler (3rd edition).

A similar "electrical tree" on the sky, produced by lightning, is also shown

on that page.

Presumably these are discharge patterns between the space charge inside
the dielectric material and the layer charge on its surface (ions of
opposite
charge from air which were attracted by the electric cloud inside). What
should such a pseudo-neutral plate be called? It is not a battery, it is not

a capacitor, it is not an electret. What is it?

And what else can a pseudo-neutral plate be used for, beside making a
decorative pattern in a transparent plastic? Suppose it is coated with a
thin layer of metal. Then, if the surface charges could be removed
electrically (how ???), one would get the net charge of the same sign
again and again.

Ludwik Kowalski