Question

The oil drop experiment by R.A. Millikan was performed to find:
$A)$ Charge on the neutron
$B)$ Charge on the electron
$C)$ Charge on the proton
$D)$ None of these

Answer 1

The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher to measure the elementary electric charge. The experiment entailed observing tiny electrically charged droplets of oil located between two parallel metal surfaces, forming the plates of a capacitor.

Complete answer:
Robert Millikan and Harvey Fletcher conducted the oil drop experiment to determine the charge of an electron. They suspended tiny charged droplets of oil between two metal electrodes by balancing downward gravitational force with upward drag and electric forces.
Millikan’s oil drop experiment measured the charge of an electron. Before this experiment, the existence of subatomic particles was not universally accepted.
Millikan’s apparatus contained an electric field created between a parallel pair of metal plates, which were held apart by insulating material. Electrically charged oil droplets entered the electric field and were balanced between two plates by altering the field.
When the charged drops fell at a constant rate, the gravitational and electric forces on it were equal. Millikan found that the charge of a single electron was $1.6 \times {10^{ - 19}}C$.
So, the correct answer is $B)$ Charge on the electron.

Note:
Some controversy was raised by historian Gerald Holton who pointed out that Millikan recorded more measurements in his journal than he included in his final results. Holton suggested these data points were omitted from the large set of oil drops measured in his experiments without apparent reason.