Millikan's oil drop experiment was a famous experiment conducted by American physicist Robert A. Millikan in 1909 to determine the charge of an electron.
Millikan used a chamber filled with air and a fine mist of oil droplets. By applying an electric field, he was able to measure the force acting on the oil droplets and calculate the charge of each droplet.
Millikan's experiment determined the charge of an electron to be 1.602 x 10^-19 coulombs, which is very close to the current accepted value. It also confirmed the existence of discrete, individual charges rather than a continuous charge.
The experiment was crucial in furthering our understanding of electricity and the nature of the electron. It also provided strong evidence for the existence of quantized charges, which eventually led to the development of quantum mechanics.
There have been some controversies surrounding Millikan's experiment, including accusations of data manipulation and inconsistencies in his methods. However, the experiment's fundamental findings have been replicated and confirmed by subsequent studies, solidifying its place in the history of science.