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Ohm, Georg Simon

conductor current flowing discovered

(1789–1854) German physicist: discovered relationship between current and voltage in a conductor.

Ohm was educated at the University of Erlangen. He held rather minor academic posts in Cologne, Berlin and Nuremberg before being appointed professor of physics at Munich in 1849.

Ohm formulated the law for which he is now best known early in his career, in 1827, but received little recognition for 20 years. Ohm’s Law states that the current flowing in a conductor is directly proportional to the potential difference across it, provided there is no change in the physical conditions (eg temperature) of the conductor; the constant of proportionality is known as the conductance of the conductor, the reciprocal of the resistance. Ohm came to this conclusion by an analogy with work on heat flow along a metal rod. He also discovered that the human ear is capable of breaking down complex musical sounds into their component frequencies, an important conclusion but again one that was ignored at the time. The SI unit of electrical resistivity, the ohm (O), is named in his honour. It is defined as being the resistance of a conductor through which a current of one ampere is flowing when the PD across it is one volt, ie 1 O =1VA –1 . (The unit of conductivity, the inverse of resistivity, was formerly known as the mho and now the siemens.)

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