The classic Millikan oil drop experiment was the first to obtain an accurate measurement of the charge on an electron. In it$,$ oil drops were suspended against gravity by a

vertical electric field.

Assume the oil drop to be $1\mathrm{.}60m$ in radius and have a density of $960k\frac{g}{m^3}.$

$($a$)$ Find the weight of the drop.

$N$

$($b$)$ If the drop has a single excess electron, find the magnitude of the electric field strength needed to balance its weight.

$\frac{N}{C}$