His experiments also aided both Einstein and Bohr in their later research efforts. Millikan went on to demonstrate the photoelectron effect, providing a valuable proof of Albert Einstein's equations. Both numbers allowed the Danish physicist Niels Bohr to finally calculate Rydberg's constant and provided the first and most important proof of the new atomic theory. ![]() Millikan's oil-drop experiment settled the argument and determined accurately (within one part in a thousand) both the charge and, by virtue of the charge-to-mass ratio, the mass of the electron. The interaction of the drop with the electric field always occurred in discrete units, indicating that the electron charge was a single value, and that it was the same value for all different forms of electricity. By ionizing the atmosphere and monitoring the motion of multiple drops, he was able to compare the time that the drop took to fall under the influence of gravity and with the electrical plates off, against the time that it took for the drop to climb under the influence of applied voltage. His reasoned that the oil drop would pick up a charge due to friction as it entered the region between the plates. Thomson had elucidated the charge-to-mass ratio, determining that the electron had a discrete, fixed charge and mass remained.īeing an experimentalist, Millikan used a tiny, submillimeter drop of oil suspended between capacitor plates to measure the incremental charge on an electron. Although the work of the English physicist J. Determined to ascend in academic rank, Millikan began his research into the charge on the electron.Īt the time, the debate over whether or not atoms were real had almost played out, but the questions surrounding the true nature of the electron were still unanswered. However, while valued activities, they did not lead to his promotion to full professor. He wrote or cowrote a number of elementary physics texts that became the classics in this field. It was as a teacher and textbook author that Millikan first made his mark. After traveling to Germany, he eventually accepted a faculty position at the University of Chicago. ![]() In 1893 Millikan began his doctoral work at Columbia University, receiving a Ph.D. It was during this period that he developed an even keener interest in physics. He enjoyed teaching physics and accepted a two-year teaching post at Oberlin upon graduation in 1891. In 1887 he enrolled in several classics classes there, and because he did quite well in Greek, at the end of his sophomore year, he was asked to teach an introductory-level physics class. In 1886 he entered Oberlin College in Ohio. ![]() When Millikan was seven, his family moved to Maquoketa, Iowa, where he attended high school. Born in Morrison, Illinois, Robert Andrew Millikan was the second son of the Reverend Silas Franklin Millikan and Mary Jane Andrews.
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