Question

A metal sphere has a charge of +8.0 µC.
What is the net charge after 6.0×10
13
electrons have been placed on it?

Answer 1

One electron has charge $-1.6 \cdot 10^{-19}$ C. Then placing $6.0×10^{13}$ electrons on the sphere will bring $- 9.6 \cdot 10^{-6} \, C$. So, total charge becomes

$-9.6 \cdot 10^{-6} +8 \cdot 10^{-6} = -1.6 \cdot 10^{-6} \, C$

Answer: $-1.6 \cdot 10^{-6} \, C$