Oil-drop experiment

Robert Millikan’s oil-drop experiment determined the elementary electric charge by balancing the electric force on charged droplets against gravity and measuring their motion.

Stokes' law: A relation connecting the drag force on a small sphere moving through a viscous fluid to its speed. Millikan inferred droplet radii from their terminal speeds using viscous drag.
Robert Millikan: An American experimental physicist who measured the elementary electric charge and the photoelectric effect. Millikan led the experiments that established the oil-drop method's famous charge measurement.
Electron: A negatively charged elementary particle found in atoms and many forms of matter. The droplet charge measurements established the magnitude of the electron's charge.
Charge quantization: The principle that electric charge is restricted to discrete multiples of a fundamental unit. The experiment supported discrete charge values, rather than a continuously variable charge model.
Terminal velocity: The constant speed reached when an object's drag balances the net force driving its motion. A droplet's falling terminal speed let Millikan estimate its radius and gravitational force.
Harvey Fletcher: An American physicist who collaborated with Millikan on the oil-drop experiment as a doctoral student. Fletcher later described his substantial role in developing and carrying out the experiment.
Elementary charge: The magnitude of the charge of a proton, equal to that of an electron. Its measured value anchors charge scales throughout physics.
Millikan's oil-drop data selection: The selective reporting of measurements in Millikan's published oil-drop experiment, later examined by historians of science. Published records include fewer observations than Millikan's laboratory notebooks, raising questions about selection and reporting.
Electric field: A physical field that exerts force on electric charges. The adjustable field between the plates supplied the upward force used to suspend droplets.
J. J. Thomson: A British physicist who discovered the electron and measured its charge-to-mass ratio. Thomson's earlier electron measurements made a separate determination of charge necessary.

Linked from 6 pages