From: SFPhysics@aol.com
Date: Fri Jul 28 2000 - 04:05:03 PDT
From: SFPhysics@aol.com Message-ID: <61.5ca0845.26b2c2df@aol.com> Date: Fri, 28 Jul 2000 07:05:03 EDT Subject: Van De Graaff electrostatic generators
> I don't know if
> it's really necessary to have a generator that produces 400,000 V, but I
> also don't want to invest in a machine that isn't extremely effective in
the
> classroom. Anyone have any advice?
> Thank you!
> Coco Ballantyne
> Eastside College Preparatory School
> East Palo Alto, CA
Dear Coco:
I own several Van De Graaffs and find that the easiest model to take around
is the little 200KV units that sell for $120. These are the same ones Welch,
Edmund, and others sell for $166. My largest unit, a million Volt monster, I
made myself for only $40 but you would need a school shop with some machine
tools to do the same.
I don't have any trouble keeping my units working even at the high humidity
of Abraham Lincoln High in San Francisco overlooking the ocean. The key is
cleanliness, especially the vertical column. Fingerprints, palmprints, etc.
degrade the ability of the column to withstand surface charge leakage. The
collector sphere should be kept clean also. All microscopic dust particles
(which are immediately drawn to the unit by electrostatic charge) create
little discharge points and your unit quickly will not work at full
efficiency. A second thing to do with your unit is to keep the lower and
upper belt rollers as clean as possible. When not in use I take the belts
off of the units and store them in a ziplock baggy. Clean the unit with a
lint free lab towel using a mild spray solution (409) but avoid rubbing
alcohol as most common isopropyl products have a small amount of oil added to
replace skin oils.
The 200KV unit will do all of the most famous demonstrations from Volta's
Hail Storm through the Saint Elmo's Whirligig. It goesn't do a great job of
getting hair to stand up on end because it is slow in charge transfer and a
human can lose charge quickly. That is the one experiment when a really dry
day is called for. The 200KV unit is made by Lee Scientific and is sold more
cheaply direct than through the big science catalogue educational outlets.
Best of luck to you,
Al Sefl
Who owns his own lab equipment and never pays retail.... such a deal ! ;-)
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