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IONS on metals/dielectrics



Dear Sam,

This is a way out, side issue, that doesn't count for much, but I am
left with another curiosity that I am incapable of proving by experiment
but I believe down deep inside that it will be as I suggest.
-----Sam said -----------------------------------------------------

First let me say that electrons do not jump off a belt in a Van de
Graaff generator. If this were true, a V.G. would work if the inside of
the column were a perfect vacuum, but this is not true.

----- My reply #1---------------------------------------------------

When playing with my "Rube Goldberg" machine, I found that the brushes
could also touch the belt. I don't remember if it reduced the voltage
generation or not, but it still threw sparks. If the brushes can touch
the belt then there is no need for ionization of the medium and the
system should be able to work in a vacuum. I do have a vacuum pump but
it is not big enough to pull a very good vacuum on my living room and at
this time I don't have an air tight cover for the
motor/belt/pulley/brushes/support combination. So this experiment must
wait till later.

----My reply #2----------------------------------------

One other area that is slightly pertinent to the brush issue but I have
no idea how pertinent.

For a number of years I have been following the design of a new concept
of vacuum tubes. Instead of a heated filament the cathode is an
extremely fine point. At last report some one had developed a silicon
metal point only a few molecules wide at the tip.

These tubes had a conventional plate and grid, and electrons were drawn
directly from the tip by a relatively low positive plate voltage. Much
of this work has been done in an attempt to radiation harden computer
and communications hardware. The Big Boys were saying that they could
package a hundred of these field emission tubes in a cubic inch.

Possibly, with the voltages that we are working with, a less than
perfect point would supply sufficient "field emission" in a vacuum
operated VGM. Surely some reciprocity theorem would allow the points to
work in reverse at the other end of the belt. Might that be called
"field absorption"?

-----------------------------------------------------------------
Your description of the generation of charge was terrific and I will use
it with my next batch of kids.

Please bear with my questions. Electrostatics is a field that has
fascinated me for years and I have never before known any experts, who
were also interested, that would talk to me about it. The thread will
soon change and I will crawl back into my hole.

Bill

Note To Bob: Thanks for the comment on keeping the thread consistent. I
will have to find out how to use software on the "subject" line. Maybe
Netscape doesn't work that way. Are there many hams on this list?