Ohm, Georg Simon (1789–1854)

German physicist who studied electricity and discovered the fundamental law that bears his name (see Ohm's law). The SI unit of electrical resistance, the ohm, is named after him, and the unit of conductance (the inverse of resistance) was formerly called the mho, which is ‘ohm’ spelled backwards.

Ohm was born and educated in Erlangen, Bavaria. He worked as a schoolteacher until 1833, when he became professor of physics at the Polytechnic Institute, Nürnberg, moving to Munich University 1849.

Ohm began the work that led him to his law of electricity in 1825. He investigated the amount of electromagnetic force produced in a wire carrying a current, expecting it to decrease with the length of the wire in the circuit. Using a thermocouple because it produced a constant electric current, he employed an electroscope to measure how the tension varied at different points along a conductor to verify his law, and presented his arguments in mathematical form in his great work Die Galvanische Kette 1827.

Ohm's law states that the steady electrical current in a metallic circuit is directly proportional to the constant total electromotive force in the circuit.