How many excess electrons does the dome of a van de Graff generator posses? What is the increase in mass because of their presence?

Question

Physics/Chemistry:

The dome of a van de Graff generator carries a negative charge of 8.0 x 10-7C.

How many excess electrons does it posses? What is the increase in mass because of their presence?

I'm just asking for a step-by-step solution or an explanation.

Answer 1

1) Use dimensional analysis:

8.0 x 10^-7C (1 e/ 1.6*10^-19 C) = 5 * 10¹² excess electrons

 

2) Use dimensional analysis:

5 * 10¹² e (9.11 * 10^-31 kg / e) = 4.555 * 10^-18 kg