Physics: Oil drop experiment

Electromagnetism Atomic Physics

Oil drop experiment By: Robert Millikan (1909)

The oil drop experiment was performed by Robert A.

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Source: Wikipedia

Oil drop experiment (1909) Performed by: Robert Millikan The oil drop experiment was performed by Robert A.

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What makes Oil drop experiment significant? This experiment is remembered because it gave scientists a way to directly test a theory about nature rather than just theorizing about it. The result either confirmed or challenged what physicists believed at the time.

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About Oil drop experiment The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). The experiment took place in the Ryerson Physical Laboratory at the University of Chicago. Millikan received the Nobel Prize in Physics in 1923. The experiment observed tiny electrically charged droplets of oil located between two parallel metal surfaces, forming the plates of a capacitor. The plates were oriented horizontally, with one plate above the other. A mist of atomized oil drops was introduced through a small hole in the top plate; some would be ionized naturally. First, with zero applied electric field, the velocity of a falling droplet was measured. At terminal velocity, the drag force equals the gravitational force. As both forces depend on the radius in different ways, the radius of the droplet, and therefore the mass and gravitational force, could be determined (using the known density of the oil). Next, a voltage inducing an electric field was applied between the plates and adjusted until the drops were suspended in mechanical equilibrium, indicating that the electrical force and the gravitational force were in balance. Using the known electric field, Millikan and Fletcher could determine the charge on the oil droplet. By repeating the experiment for many droplets, they confirmed that the charges were all small integer multiples of a certain base value, which was found to be 1.5924(17)×10−19 C, about 0.6% difference from the currently accepted value of 1.602176634×10−19 C. They proposed that this was the magnitude of the negative charge of a single electron.