Robert Millikan won the 1923 Nobel Prize in Physics for his work on the elementary charge of electricity and the photoelectric effect. His oil-drop experiment measured the charge carried by individual tiny droplets and established the basic unit of electric charge.
In the experiment, Millikan sprayed oil droplets into a chamber and observed them between electrically charged plates. By balancing electrical and gravitational forces, he could calculate the droplets’ charges. The values appeared as whole-number multiples of a smallest unit, the elementary charge.
Millikan also tested Einstein’s 1905 explanation of the photoelectric effect. His measurements supported the relationship between light frequency and the energy of emitted electrons, although Millikan himself was initially skeptical of Einstein’s light-quantum interpretation.
The Nobel citation names both parts of his work. Millikan’s accepted name is Robert Andrews Millikan; “Robert Millikan” is the standard short form. The elementary charge is approximately 1.602 × 10−19 coulomb.