Beléndez.Ī spray formed oil-drops, some of which fell through a small gap into a uniform, electrical field area space by two parallel, charged plates. Diagram of the apparatus used by Millikan to measure the charge of the electron. As the electrical field was known, it was possible to determine the accumulated charge on the oil-drop. In his experiment, Millikan measures the electrical force on a small oil-drop that has been charged by an electrical field created between two electrodes when the drop was in the gravitational field. The fundamental electric charge is one of the basic constants in physics, consequently, its accurate determination is essential for this discipline. He had earned great renown as a physics lecturer, but had still not achieved anything noteworthy as a scientific investigator. When Millikan began a long series of experiments in 1907, he had already been working at the University of Chicago for ten years, had got married, was the father of three children and about to celebrate his fortieth birthday. Millikan, with the aid of Harvey Fletcher, one of his doctoral students, used the oil-drop experiment to measure the charge of the electron (and with this, its mass). Accordingly, if it was possible to determine one of these values separately (charge or mass), the other could be easily calculated. Thomson, the British physicist, had already established the charge-to-mass ratio of the electron back in 1897, but neither of them separately. Millikan’s first great achievement was to determine the charge of the electron, to which end he used the “oil-drop method”. If required to classify him as a physicist, his facet as an experimental physicist would undoubtedly have to be highlighted, as would the numerous important discoveries he made, predominantly in the fields of optics and molecular physics. Millikan was a key figure in the development of physics in the United States in the first half of the 20th century. In the course of his life (he died in 1953) Millikan was a Professor of Physics, Director of the Norman Bridge Physics Laboratory and President of the California Institute of Technology (CALTECH). He was eventually to become a lecturer there (1910), a post he held until 1921. Michelson to become his assistant in the recently founded Ryerson Laboratory at the University of Chicago. After spending a year (1896) in Germany at the Universities of Berlin and Götingen, he return to the United States to take up an invitation from the physicist and fellow Nobel Laureate Albert A. In 1893 he was awarded a fellowship at Columbia University, from which he received his PhD in 1895 for a thesis on the polarization of light emitted by incandescent surfaces. A phenomenon that had originally been observed (1824) by François Aragó, Millikan used molten gold and silver from the US Department of Treasury to prove his thesis. After graduating from Oberlin College in Ohio (1891) -where he particularly enjoyed studying Greek and mathematics- he did two courses in elementary physics, which awakened his interest in this discipline. Robert Andrews Millikan was born in Morrison, Illinois (USA) on March 22, 1868. Indeed, it is considered to be one of “most beautiful experiments in physics” and was pivotal in enabling the measurement of the charge of the electron Robert Andrews Millikan (1868-1953). One of the most famous and important of these was that which enabled the determination of the charge of the electron, conducted by Millikan in 1909, which has become known as the oil-drop experiment or simply Millikan’s experiment. There are numerous examples of decisive experiments in the history of physics. Physics requires experiments, accurate measurement and, of course, conclusions to be drawn. There is little doubt, however, that inside the apparatus used by Millikan there was a world of particles with which he became so familiar that he unblushingly claimed to see things in that world. Quite often we physicists say that we see those things on which we are working, no matter how small, or even abstract they may be. “He who has seen that experiment, and hundreds of investigators have observed it, has literally seen the electron”. In his Nobel Lecture “The Electron and the Light-Quant from the Experimental Point of View” he referred to the experiment that had enabled him determine the charge of the electron, leaving his audience convinced that he had seen electrons: “for his work on the elementary charge of electricity and on the photoelectric effect”. In 1923, the American physicist Robert Andrews Millikan (1868-1953) was awarded the Nobel Prize for Physics ,
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