Date: Wed, 03 Nov 2010 17:15:11

Author: Adam Beehler

Subject: Van de Graaff Generator and Lightning Rod


I set up a lightning rod demo for an instructor using the Van de Graaff
(VDG) generator. Basically, a grounded sphere is slowly pulled away
from the dome of the running VDG until the spark between them is as
large as can be maintained. Then a small pointed metal object is placed
on top of the VDG dome and we try again. This time the grounded sphere
can only be separated from the VDG dome by a small distance. The small
pointed metal object allows charge to leak from the VDG dome and keeps
it from getting to as high a potential. This is what I told him to
expect. Of course, after class he asks me why the VDG sparked at all
with the small pointed object. I guess he told his class the same
reasoning as mentioned above, but he expected so much of the charge to
leak away that NO spark would form at all.

Well, I bring this all up because quite often sharp little points keep
our electrostatic demos from working at all, so why is not this
instructor right this time?

Adam Beehler

P.S. I tried several sharp points but to no avail.

P.S.S. I just assume that the charge cannot leak away fast enough.