Millikan Oil Drop Apparatus
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A metal cylinder, approximately thirty-six inches tall and twenty-four inches in diameter with two internal horizontal plates and several openings used for lighting and viewing inside the cylinder. This unassuming metal cylinder, the Millikan Oil-Drop Apparatus, was engineered by Robert A. Millikan (1868-1953) to determine the electrical charge of a single electron. He won the Nobel Prize in Physics in 1923 for this work. Millikan figured correctly that he would be able to compute the electrical charge from the strength of the electrical field needed to counteract the gravitational force on water droplets. He began his experiment by studying the rate of fall of water droplets between two metal plates while under the influence of an electric field. When the field was turned on, a droplet moved slowly upward by magnetic attraction; when the field was turned off, the droplet moved downward by the force of gravity. Water droplets evaporated too quickly to make precise measurement possible. Millikan repeated the experiments with oil droplets. Using an atomizer (an instrument which converts liquids or solids to a fine spray, or minute particles), he generated oil droplets above the two parallel plates. Droplets fell through a tiny hole in the upper plate to the space between the plates and were observed through a short focal distance telescope. To make the droplets more visible, Millikan illuminated them from one side. Two horizontal, parallel, thin lines intersected the field of view. By turning the field on and off, Millikan could study suspended droplets individually for as long as forty-five seconds before they evaporated. By 1909 Millikan had determined that any charge on a droplet was always a whole-number multiple of an irreducible value: ”e”-the charge of an electron. Millikan’s experiments and observations proved conclusive evidence that electrons are fundamental particles of identical charge and mass. In 1913, Millikan finally announced a highly accurate value for the electronic charge of an electron that was not improved upon for many years. Millikan was born in Morrison, Illinois. He taught physics at the University of Chicago from 1896 to 1921. How we learn about communities 16 History; 10-12 Science; 13 Science, Technology and Society
|Millikan, Robert Andrews, 1868-1953|
|University of Illinois at Urbana-Champaign|
|University of Illinois at Urbana-Champaign, University Library|
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