1913+Millikan

By:Alex Benzinger **Robert Andrews Millikan** (March 22, 1868 – December 19, 1953) was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945. Starting in 1909, while a professor at the University of Chicago, Millikan and Harvey Fletcher worked on an oil-drop experiment (since repeated, with varying degrees of success, by generations of physics students) in which they measured the charge on a single electron. Professor Millikan took sole credit, in return for Fletcher claiming full authorship on a related result for his dissertationMillikan went on to win the 1923 Nobel Prize for Physics, in part for this work, and Fletcher kept the agreement a secret until his death After a publication on his first results in 1910 contradictory observations by Felix Ehrenhaft started a controversy between the two physicists After improving his setup he published his seminal study in 1913 The elementary charge is one of the fundamental physical constants and accurate knowledge of its value is of great importance. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592 × 10−19 coulomb ), the charge on a single electron. That this is somewhat lower than the modern value of 1.602 176 53(14) x 10−19 coulomb is probably due to Millikan's use of an inaccurate value for the viscosity of air. Although at the time of Millikan's oil-drop experiments it was becoming clear that there exist such things as subatomic particles, not everyone was convinced. Experimenting with cathode rays in 1897, J.J. Thomson had discovered negatively charged 'corpuscles', as he called them, with a mass to charge ratio 1/1840 times that of a hydrogen ion. Similar results had been found by George FitzGerald and Walter Kaufmann. Most of what was then known about electricity and magnetism, however, could be explained on the basis that charge is a continuous variable; in much the same way that many of the properties of light can be explained by treating it as a continuous wave rather than as a stream of photons.