An electroscope has a charge of....

Question

An electroscope has a charge of -4μC while your finer has a charge of 4.5μC. You touch the electroscope with your finger and discover that the charges of your finger and the electroscope are now the same. In this process, electrons were transferred from the electroscope to your finger. How many electrons were transferred in order for your finger and the electroscope to have the same charge?

 

Answer 1

Total charge must be conserved.

 

q = (-4 + 4.5) x 10^-6 C = 0.5 x 10^-6 C

 

Then the finger and the electroscope must both have 0.25 x 10^-6 C.  That means the finger gained -4.25 x 10^-6 C of negative charge.  Divide that by the electron charge, -1.6 x 10^-19 C, and that gives the number of electrons transferred between the two.