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The Millikens Oil Drop Experiment was an experiment performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the charge of an electron. This experiment proved to be very crucial in the physics community.
Millikan oil-drop experiment, first direct and compelling measurement of the electric charge of a single electron. It was performed originally in 1909 by the American physicist Robert A. Millikan, who devised a method of measuring the minute electric charge that is present on many of the droplets in an oil mist.
Millikan and Fletcher's experiment involved measuring the force on oil droplets in a glass chamber sandwiched between two electrodes, one above and one below. With the electrical field calculated, they could measure the droplet's charge, the charge on a single electron being ( −1.592 × 10−19 C ).
Millikan oil drop experiment aims at measuring the charge of the electron. It is perhaps the most basic of all atomic physics or so called modern physics laboratory experiments. The arrangement is quite simple and bears a testimony to the ingenuity of Robert Millikan.
THEORY. In this experiment you will use tiny droplets of oil. When these droplets fall under the influence of gravity it takes them only a few milliseconds to reach a terminal (constant) speed vf, where the downward force of gravity is balanced by the upward drag force from the air.
Millikan's experiment is based on observing charged oil droplets in free fall and the presence of an electric field. A fine mist of oil is sprayed across the top of a perspex cylinder with a small 'chimney' that leads down to the cell (if the cell valve is open).
Millikan's original papers are quite readable, and the most important one, from 1913, can be found here. Millikan's experiments were very carefully set up. He chose an oil with a very low vapour pressure so that evaporation of the drops (which would change their size) was minimised.
The experiment is one of the most fundamental of the experiments in the undergraduate laboratory. The experimental apparatus is patterned after the original apparatus, made and used by R.A. Millikan to show that electric charge exists as integral multiples of ‘e’ the charge on a single electron.
