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In retrospect

Nobel 1923: determining the charge of the electron

Nature Reviews Physics volume 5, page 553 (2023)Cite this article

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One hundred years ago, the Nobel Prize in Physics was awarded to Robert Millikan for his work on the elementary charge of electricity and on the photoelectric effect. Although he also verified Einstein’s work on the photoelectric effect, it is for determining the charge of the electron that Millikan is best known for today. He placed the value of e at 1.5924 × 10–19 C. Millikan’s value was an underestimate of 0.6%, but such was the reverence for his work that it took years of experiments to settle on the currently accepted value of 1.6021 × 10–19 C. As Richard Feynman quipped in the 1970s, “when they got a number that was too high above Millikan’s, they thought something must be wrong — and they would look for and find a reason why something might be wrong. When they got a number close to Millikan’s value, they didn’t look so hard.”

The turning point came in 1908 with the idea of replacing water with oil. The historical record is unclear on exactly whose idea this was. But very quickly, Millikan’s graduate student, Harvey Fletcher, set up a new apparatus (pictured), with a fine mist of oil suspended between the two electric plates. In a Physics Today article published in 1982, Fletcher vividly describes looking through his telescope at the oil drops between the plates and seeing “little starlets, having all colours of the rainbow”: his first observation of Brownian motion. By the end of the day, Fletcher had an estimate for the value of e. Over the next two years, Millikan and Fletcher painstakingly measured the rise and fall of different sized oil droplets, and how they were affected by the electric field. By 1910, two big results had come out from this experiment: the value of e, and the value of Ne, where N is Avogadro’s number, which was measured based on the Brownian motion observations.

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References

Original article

  • Millikan, R. A. XXII. A new modification of the cloud method of determining the elementary electrical charge and the most probable value of that charge. Lond. Edinb. Dublin Philos. Mag. J. Sci. 19, 209–228 (1910)

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Related articles

  • Millikan, R. A. On the elementary electrical charge and the Avogadro constant. Phys. Rev. 2, 109–143 (1913)

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  • Holton, G. in Historical Studies in the Physical Sciences (eds McCormmach, R. et al.) 161–224 (Johns Hopkins Univ. Press, 1978)

  • Fletcher, H. My work with Millikan on the oil-drop experiment. Phys. Today 35, 43–47 (1982)

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  • Goodstein, D. In defense of Robert Andrews Millikan. Am. Sci. 89, 54–60 (2001)

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  1. Nature Reviews Physics https://www.nature.com/natrevphys/

    Ankita Anirban

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  1. Ankita Anirban
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Correspondence to Ankita Anirban.

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Anirban, A. Nobel 1923: determining the charge of the electron. Nat Rev Phys 5, 553 (2023). https://doi.org/10.1038/s42254-023-00646-4

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