Robert Millikan

Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was a U.S. experimental physicist who won the 1923 Nobel Prize for his measurement of the charge on the electron and for his work on the photoelectric effect. He later studied cosmic rays.

Charge of the electron

In 1910, while a professor at the University of Chicago, Millikan published the first results of his oil-drop experiment (since repeated, with varying degrees of success, by generations of physics students) in which he measured the charge on a single electron. The so-called 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 1.60217653×10-19 coulomb is probably due to Millikan's use of a somewhat inaccurate value for the viscosity of air.

Related Topics:
1910 - Professor - University of Chicago - Oil-drop experiment - Elementary charge - Physical constants - Integer - Coulomb - Viscosity - Air

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Controversy

Subsequently, maverick physicist Felix Ehrenhaft claimed to have performed a similar experiment and observed charges smaller than Millikan's elementary charge. Ehrenhaft stated that the "variability of e" supported the aether theory and existence of subelectrons. This led Millikan to a further series of measurements which he published in 1913 to reassert his original results. Controversy has arisen because, although Millikan states in his paper that "It is to be remarked, too, that this is not a selected group of drops, but represents all the drops experimented upon during 60 consecutive days...", his laboratory notebooks show that he recorded data on 175 drops in the period between November 11 1911 and April 16 1912 The calculations of results did not match the totality of the series, because he reported only 58 in his paper.

Related Topics:
Felix Ehrenhaft - Elementary charge - Aether theory - Subelectron - 1913 - November 11 - 1911 - April 16 - 1912

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The reaction was exacerbated because his notebooks feature phrases such as "very low something wrong" and This is almost exactly right & the best one I ever had!! Though accusations have been made that Millikan was guilty of fraud and pathological science, some believe that he was using his experimental insight and personal expertise on the subject-matter to reject unreliable observations on sound physical grounds. According to Goodstein, research has shown that an analysis of the totality of his data does not lead to substantially different results.

Related Topics:
Fraud - Pathological science

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