Robert Millikan

Robert Andrews Millikan (1868–1953) was an American experimental physicist who measured the electron’s charge with oil drops and advanced research on the photoelectric effect.

Oil-drop experiment: An experiment that measured the elementary electric charge by balancing forces on charged oil droplets. Millikan used suspended droplets to determine the electron’s charge.
Stokes' law: A formula for the viscous drag on a small sphere moving slowly through a fluid. It helped relate an oil droplet’s motion to its size and weight.
Harvey Fletcher: An American physicist who collaborated with Millikan on the oil-drop experiment as a graduate student. Fletcher later described his substantial role in developing the experiment.
Electron: A negatively charged subatomic particle found in atoms and free in many physical systems. Millikan’s charge measurement helped establish the electron as a quantifiable physical entity.
Photoelectric effect: The emission of electrons from matter when it absorbs light of sufficient frequency. Millikan measured how emitted electrons’ energies varied with light frequency.
Electric field: A physical field that exerts force on electric charges. Millikan adjusted an electric field to suspend charged droplets against gravity.
Albert Einstein: A theoretical physicist whose work transformed modern physics, including an explanation of the photoelectric effect. Millikan’s experiments tested Einstein’s account while Millikan initially doubted its interpretation.
Nobel Prize in Physics 1923: The 1923 Nobel Prize in Physics, awarded to Robert A. Millikan for work on the elementary charge and photoelectric effect. The award recognized the experimental achievements that defined Millikan’s public legacy.
Elementary charge: The magnitude of the electric charge carried by a proton or, with opposite sign, an electron. The oil-drop experiment produced a precise value for this fundamental quantity.
Quantization of electric charge: The principle that observable electric charge occurs in integer multiples of an elementary unit. Repeated droplet measurements revealed charges clustered around whole-number multiples.

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