oljedroppsexperiment

The oil-drop experiment, also known as Millikan's oil-drop experiment, was a landmark physics experiment performed by Robert Millikan and Harvey Fletcher in 1909. The primary goal of the experiment was to measure the electric charge of a single electron.

In the experiment, fine droplets of oil were sprayed into a chamber. These droplets, due to friction during spraying, acquired a net electric charge. The chamber contained two parallel metal plates, with a voltage applied between them. This created an electric field that could be adjusted. The oil droplets were observed through a microscope as they fell under gravity. By adjusting the electric field, Millikan could suspend some of the oil droplets in mid-air, balancing the downward force of gravity with the upward force of the electric field.

The experiment relied on the principle that the electric force on a charged object in an electric field is equal to the charge of the object multiplied by the electric field strength. By measuring the rate at which the droplets fell in the absence of an electric field, their mass could be calculated using Stokes' Law. Then, by adjusting the electric field to suspend a droplet, the electric force could be determined. Knowing the electric field strength and the electric force, the charge on the oil droplet could be calculated.

Millikan and Fletcher repeated this measurement for thousands of oil droplets. They observed that the charges on the droplets were always integer multiples of a fundamental, smallest charge. This fundamental charge was identified as the charge of a single electron. The oil-drop experiment provided direct experimental evidence for the quantization of electric charge and yielded a precise value for the elementary charge, which is approximately 1.602 x 10^-19 coulombs. This result was crucial for the development of atomic physics and solidified the concept of the electron as a fundamental particle.