Questions about Van de Graaff generator

Only asking those questions because I can't afford to get a real generator.

1. If the voltage on the sphere was 50 kV, then I used a metal rod to discharge it and I connected a voltmeter to wire grounding the rod, will it read 50 kV?

2. Does the formula $V=kq/r$ apply for the generator? (According to some sites, it does.) If it does, which radius is meant? The hollow part radius? Will the thickness of the wall matter?

1 Answer

If the voltmeter is able to measure such high voltages and has a very high internal resistance you can connect it between the sphere and ground and it will display 50kV.

The thickness of the wall doesn't matter at all. So r is the external radius.

• so according to the photo i just uploaded, which one is the r in the formula , the red one or the yellow one? Jan 26, 2014 at 22:00
• The yellow one - or more precisely - half of the yellow line. Jan 26, 2014 at 22:08
• i asked a friend he said : the electrostatic excess charge will be on the surface of the sphere , so it won't matter if the sphere was hollow or not, is this statement right? Jan 27, 2014 at 7:21
• Yes it doesn't matter whether the sphere is hollow or not. Jan 27, 2014 at 7:39