- In full:
- Robert Andrews Millikan
- Born:
- March 22, 1868, Morrison, Illinois, U.S.
- Died:
- December 19, 1953, San Marino, California (aged 85)
- Awards And Honors:
- Nobel Prize (1923)
- Subjects Of Study:
- Planck’s constant
- electron charge
- photoelectric effect
Robert Millikan
-
Who was Robert Millikan?
Robert Millikan (1868–1953) was an American physicist who won the Nobel Prize in Physics in 1923 for his work on the elementary electronic charge and the photoelectric effect.
After earning a doctorate from Columbia University in 1895, Millikan became a professor at the University of Chicago in 1910. Around this time, he began experiments to determine the electric charge of a single electron, using charged water droplets in an electric field. He then used oil in his famous oil-drop experiment and was able to measure the charge of the drop.
In 1916, Millikan verified Albert Einstein's equation describing the photoelectric effect, further proving Einstein's theory and obtaining an accurate value of Planck's constant.
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What is Robert Millikan famous for studying?
Robert Millikan, an American physicist, is renowned for his work on the elementary electronic charge and the photoelectric effect.
His famous oil-drop experiment (first performed in 1909) allowed for the first direct and compelling measurement of the electric charge of a single electron. By observing the behavior of charged oil droplets in an electric field, Millikan was able to determine that the charge on the droplets was always a multiple of a basic value, which he identified as the elementary electric charge (approximately 1.602 × 10−19 coulomb). Millikan's experiment offered convincing proof that electric charge exists in basic natural units.
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What was the oil-drop experiment?
The Millikan oil-drop experiment directly measured the electric charge of a single electron. In the experiment, Robert Millikan sprayed a fine mist of oil droplets into a closed chamber between two parallel metal plates. As the oil drops fell through a hole in the top plate, radiation ionized the space, causing electrons to attach to the drops and give them a negative charge.
By measuring the electric force and field on the charged oil droplets, Millikan determined the magnitude of the charge itself. He adjusted the voltage between the plates to suspend the droplets, balancing electric and gravitational forces. Through repeated trials, he found that the charge on individual drops was always a multiple of a basic value, the elementary electric charge (approximately 1.602 × 10⁻¹⁹ coulomb), thus proving that electric charge exists in natural units. For this and his work on the photoelectric effect, Millikan received the Nobel Prize in Physics in 1923.
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How did the oil-drop experiment help measure the charge of an electron?
Robert Millikan's oil-drop experiment directly measured the electric charge of a single electron. In the experiment, Millikan sprayed a fine mist of oil droplets into a chamber between two metal plates. As the oil drops fell through a hole in the top plate, they acquired a negative charge from ionized air.
By adjusting the voltage between the plates, Millikan could suspend the charged droplets. Measuring the voltage and mass of a droplet allowed him to determine its overall electric charge. He found that the charge values were always multiples of a lowest value, which he identified as the elementary electric charge, approximately (1.602 \times 10^{-19}) coulomb. Millikan's method offered proof that electric charge exists in basic natural units.
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What other contributions did Robert Millikan make to physics?
Robert Millikan, an American physicist, was renowned for his work on the elementary electronic charge and the photoelectric effect, earning the Nobel Prize in Physics in 1923.
Beyond this, Millikan made other significant contributions to physics:
* Oil-Drop Experiment In 1909, Millikan began experiments to determine the electric charge carried by a single electron. By 1910, he obtained precise results with his famous oil-drop experiment, which offered convincing proof that electric charge exists in basic natural units.
* Photoelectric Effect In 1916, Millikan experimentally verified Albert Einstein's equation describing the photoelectric effect, which involves electrons being ejected from a metal plate when light falls on it. Millikan's measurements proved Einstein's theory and obtained an accurate value of Planck's constant.
* Cosmic Rays After becoming director of the Norman Bridge Laboratory of Physics at the California Institute of Technology (Caltech) in 1921, Millikan studied radiation from outer space, proving its extraterrestrial origin and naming it "cosmic rays".
* Electronics In 1909, Millikan measured the electric charge of an electron.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is Millikan's work important to science today?
Robert Millikan's work remains significant to science, notably his oil-drop experiment that offered direct proof of electric charge existing in natural units. This experiment allowed for measuring the elementary electronic charge. Millikan's determination of the elementary charge is a fundamental physical constant. His work also confirmed Einstein’s theory regarding the photoelectric effect and yielded an accurate value for Planck’s constant.
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Robert Millikan (born March 22, 1868, Morrison, Illinois, U.S.—died December 19, 1953, San Marino, California) was an American physicist honored with the Nobel Prize for Physics in 1923 for his study of the elementary electronic charge and the photoelectric effect.
Millikan graduated from Oberlin College (Oberlin, Ohio) in 1891 and obtained a doctorate at Columbia University in 1895. In 1896 he became an assistant at the University of Chicago, where he became a full professor in 1910. During his time in Chicago as an assistant professor, he wrote for high-school and college students several physics textbooks that entered widespread use.
In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electric field. The results suggested that the charge on the droplets is a multiple of the elementary electric charge, but the experiment was not accurate enough to be convincing. He obtained more precise results in 1910 with his famous oil-drop experiment in which he replaced water (which tended to evaporate too quickly) with oil. Millikan varied the electric voltage between two metal plates as an oil drop fell between them until the drop stopped falling. When the drop was stationary, the downward force of gravity on the drop equaled the upward electrical force on the charges in the drop, and then Millikan could measure how much charge the drop had.
In 1916 he took up with similar skill the experimental verification of the equation introduced by Albert Einstein in 1905 to describe the photoelectric effect, in which electrons are ejected from a metal plate when light falls on it. The photoelectric effect had puzzled physicists, but Einstein described the energy of the ejected electron as equal to hf - φ, where h is Planck’s constant, f is the frequency of the light, and φ is a property of the metal called the work function. Einstein’s description of the photoelectric effect as a quantum phenomenon was controversial, but Millikan’s measurements proved Einstein’s theory and obtained an accurate value of Planck’s constant. When the United States entered World War I in 1917, he became vice chairman of the National Research Council in Washington, D.C., where he helped scientists apply their research to the war effort. He returned to Chicago in 1919.
In 1921 Millikan left the University of Chicago to become director of the Norman Bridge Laboratory of Physics at the California Institute of Technology (Caltech) in Pasadena. There he undertook a major study of the radiation that the physicist Victor Hess had detected coming from outer space. Millikan proved that this radiation is indeed of extraterrestrial origin, and he named it “cosmic rays.” As chairman of the executive council of Caltech from 1921 until his retirement in 1945, Millikan turned that school into one of the leading research institutions in the United States.