Robert Andrews Millikan (1868 - 1953) was an American experimental physicist best known for measuring the electric charge carried by a single electron. Through his celebrated oil-drop experiment he determined the value of the elementary charge with unprecedented precision, and his subsequent work confirmed Albert Einstein's equation for the photoelectric effect. For these achievements he was awarded the Nobel Prize in Physics in 1923. [1]
Early life and education
Millikan was born on 22 March 1868 in Morrison, Illinois, the son of a Congregational minister. He studied at Oberlin College, where he first encountered physics, and went on to earn his doctorate at Columbia University in 1895. He continued his training in Germany before joining the faculty of the University of Chicago, where he taught and conducted research for more than two decades. [2]
The oil-drop experiment
Working at the University of Chicago in the years around 1909 to 1913, Millikan devised an ingenious method to isolate and measure the charge on individual tiny droplets of oil suspended between charged plates. By balancing gravity against an electric field, he showed that the charge always appeared as a whole-number multiple of a single fundamental unit, providing strong evidence that electric charge is quantized. His measurement of the elementary charge became one of the most accurate physical constants of its era. [1][3]
The photoelectric effect
Millikan then turned to the photoelectric effect, in which light striking a metal surface ejects electrons. Although he was initially skeptical of Einstein's photon-based explanation, his meticulous experiments confirmed the linear relationship Einstein had predicted and yielded an independent determination of Planck's constant. This work provided crucial experimental support for the emerging quantum theory of light. [3]
Later research and Caltech
In 1921 Millikan moved to Pasadena, California, to lead the institution that became the California Institute of Technology (Caltech), serving as chairman of its executive council. Under his leadership Caltech grew into a leading center for scientific research. He also studied high-energy radiation reaching the Earth from space, popularizing the term "cosmic rays" to describe it. [2]
Legacy
Millikan received numerous honors in addition to the Nobel Prize, including the Hughes Medal, the Franklin Medal, the Edison Medal, and the Comstock Prize in Physics. He was a prolific author of textbooks that shaped physics education for generations of students. He died on 19 December 1953 in San Marino, California, remembered as one of the foremost experimental physicists of the early twentieth century. [4]
