This is just a conceptual question. I have an electroscope with a needle inside

Question

This is just a conceptual question.

I have an electroscope with a needle inside and a plate on top. When holding a positively charged rod close to it the needle moves, and I understand that this is due to the movement of electrons from the neutrally charged needle and up to the plate, leaving the needle on the bottom more positively charged.

But, what happens when you actually touch the rod to the plate, i know there must be some sort of exchange or electrons but how does this work? does it simply balance the charge between the two connecting objects?

Also, how can the net charge be defined in this case. If you don't actually touch the Rod to the plate is the net charge zero due to no exchange? Basically what is the net charge and how is it defined when the rod is touching and when it isnt touching, and when it touches and is removed. thanks a bunch!

Explanation / Answer

Charges are conservative. That is if a positive charge is produced a negative charge must be produced also. In the case when the rod is not touching the electroscope there is no charge produced, only the movement of electrons due to Coloumbs's Law. However, when the rod touches the electroscope, the response must be that in order for charge to be conserved, something must be produced (and that is the extra +and -) and hence the conservation of charge will still stand. No one really knows how or why charge is produced, that is just the way it is. Hope this answers your questions.

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