How many excess electrons must you add to an object to give it a charge of - 6.50 μc?

Micro = 10^-6

n = nano = 10^-9

(a) - 2.5 micro coulombs = - 2.5 X 10^-6

The charge on a electron is always - 1.60 X 10^-19.

So, given charge divided by charge on electron gives you number of electrons.

(-2.5X10^-6) / (-1.60X10^-19) = 1.5625 X 10^13 excess electrons.

(b) - 2.5 nano coulombs = - 2.5 X 10^-9

The charge on a electron is always - 1.60 X 10^-19.

So, given charge divided by charge on electron gives you number of electrons.

(-2.5X10^-9) / (-1.60X10^-19) = 1.5625 X 10^10 excess electrons.

Round my answers to 3 significant figures if needed or to the appropriate form asked by the question.