Physics (AS & A Level) · Oct / Nov 2019 · Paper 12 · Question 30

A charged oil drop of mass m, with n excess electrons, is held stationary in the uniform electric field between two horizontal plates separated by a distance d. The voltage between the plates is V, the elementary charge is e and the acceleration of free fall is g. What is the value of n?

1. A\frac{mgd}{eV}
2. B\frac{eV}{mgd}
3. C\frac{meV}{gd}
4. D\frac{gd}{meV}

As printed in the paper