Q. In 1909 Robert Millikan was the first to find charge of an electron in his now-famous oil drop experiment. In the experiment, tiny oil drops are sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops are observed with a magnifying eyepiece, and electric field is adjusted so that the upward force on some negatively charged oil drops is just sufficient to balance the downward force of gravity. That is, while suspended, upward force qE just equals mg. Millikan accurately measured the charges on many oil drops and found the values to be whole-number multiples of 1.6 x 10^-19C -- the charge of the electron. For this he won the Nobel Prize.

(a) If a drop of mass 6.82449 x 10^-13 kg remains stationary in an electric field of 1.1 x 10^6 N/C, what is the charge of this drop?

(b) How numerous extra electrons are on this particular oil drop (given the presently known charge of the electron)?