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I am currently experimenting with a homemade Van de Graaff generator. The design looks just like in the Wikipedia page here. In many designs of the VDG, I see that the bottom comb is connected to a metal sphere. The Wikipedia page said that it is also connected to the ground.

In the example, the wand with metal sphere (8) is connected to ground, as is the lower comb (7); electrons are drawn up from the ground due to the attraction by the positive sphere ...

If it's connected to ground, which I understand is a virtually limitless reservoir of free charges, why is the metal sphere charged and not neutral?

My intention is to have the VdG generator in one place and use the charge it produces in some other places (not too far) in a distance and I wonder if I can use the metal sphere.

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I think the problem arrives in the way the diagram on wikipedia shows the negative charges to sit on the wand and its metal sphere. While the large metal sphere is being positively charged, (actually it is having its negative charge stripped), these negative charged are carried by the belt towards the grounded earth, and thus 'disappear'. However once the wand comes close enough to the metal sphere, negative charges in the wand become attracted and pull other negative charges out of the earth. These charges 'jump' in a spark to the metal sphere and neutralize it. The wand is not negatively charged while the belt is running as the diagram might lead you to believe.

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  • $\begingroup$ What if I do not connect the metal sphere to a ground? Would the generator work? $\endgroup$ – gregory112 Sep 29 '20 at 8:23

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