[Phys-L] measure voltage of van de Graaf

[Carl Mungan <mungan@usna.edu>]

I have a large capacitor (two Al disks, roughly 50 cm in diameter and
spaced by 12 cm) connected to a van de Graaf (the usual classroom style
model, top dome about 25 cm in diameter). I'd estimate the voltage to be
about 100 kV, implying a charge on the capacitor plates of about +/- 1 uC.
I'd like to measure more precisely. Obviously either a measurement of V or
Q would work.

Simplest idea I can think of is to progressively reduce the plate spacing
until I get arcing and then assume V = (3 kV/mm) * (arcing plate spacing).

But is there a better way? I'm looking for something simple (no fancy
equipment beyond standard undergrad lab stuff) and safe, but accurate.

-- 
Carl E Mungan, Assoc Prof of Physics  410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/