What Did Robert Millikan Discover

Millikan oil-drib experiment, first straight and compelling measurement of the electrical charge of a unmarried electron. It was performed originally in 1909 past the American physicist Robert A. Millikan, who devised a straightforward method of measuring the minute electric charge that is nowadays on many of the aerosol in an oil mist. The force on any electrical charge in an electrical field is equal to the product of the accuse and the electric field. Millikan was able to mensurate both the amount of electric force and magnitude of electric field on the tiny charge of an isolated oil droplet and from the data make up one's mind the magnitude of the charge itself.

Millikan's original experiment or any modified version, such as the post-obit, is called the oil-driblet experiment. A closed chamber with transparent sides is fitted with two parallel metallic plates, which larn a positive or negative charge when an electric current is practical. At the kickoff of the experiment, an atomizer sprays a fine mist of oil droplets into the upper portion of the chamber. Under the influence of gravity and air resistance, some of the oil droplets fall through a small pigsty cut in the top metal plate. When the space between the metal plates is ionized by radiations (eastward.yard., X-rays), electrons from the air attach themselves to the falling oil aerosol, causing them to acquire a negative accuse. A light source, gear up at right angles to a viewing microscope, illuminates the oil aerosol and makes them appear every bit vivid stars while they fall. The mass of a single charged droplet can be calculated by observing how fast information technology falls. By adjusting the potential difference, or voltage, between the metal plates, the speed of the droplet'south motion can be increased or decreased; when the corporeality of upward electric force equals the known down gravitational strength, the charged droplet remains stationary. The amount of voltage needed to suspend a droplet is used along with its mass to determine the overall electric accuse on the droplet. Through repeated application of this method, the values of the electric charge on private oil drops are ever whole-number multiples of a lowest value—that value being the elementary electric accuse itself (about 1.602 × 10⁻¹⁹ coulomb). From the fourth dimension of Millikan's original experiment, this method offered convincing proof that electric charge exists in basic natural units. All subsequent distinct methods of measuring the bones unit of electric accuse betoken to its having the aforementioned fundamental value.

Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.