A spherical oil drop, radius `10^(-4)` cm has on it at a certain a total charge of 40 electrons. Calculate the energy that would be required to place an additional electron on the drop.

Explanation

Initial charge on the oil drop = 40 `xx 1.6 xx 10^(-19)`C.
Potential .of the oil drop = `(q)/(4 pi epsilon_(0)r)`
= 9` xx 64 xx 10^(-4)` volts.
now energy equired = work done in bringing an electron from infinity to a point of potential `9 xx 64 xx 10^(-4)` volts.
As, Potential = `("work")/("charge")`
`therefore` Work = potential `xx` charge = `9 xx 64 xx 10^(-4) xx 1.6 xx 10^(-19) = 921.6 xx 10^(-23)` joules.