In his experiment, Millikan sprayed electrically charged oil droplets into a container between two parallel plates. He applied a potential difference between the plates to create an electric field. Due to gravity, the drops began to fall, but the electric field slowed them down. They measured the speed at which the droplets fell and adjusted the electric field until the droplets were suspended, which meant that the electric force exactly balanced the force of gravity. By observing how the droplets moved under the influence of the electric field, Millikan was able to calculate the electric charge of each droplet. He discovered that the charges of the droplets were always multiples of a minimum charge, which was later identified as the charge of the electron. Calculating the electron mass Using the electron charge he had determined and combining it with data on the behavior of oil droplets in the electric field and gravity, Millikan was able to calculate the electron mass.
