In 1834 the French physicist Jean C. A. Peltier discovered an effect inverse to the Seebeck effect: If a current passes through a thermocouple, the temperature of one junction increases and the temperature of the other decreases, so that heat is transferred from one junction to the other. The rate of heat transfer is proportional to the current and the direction of transfer is reversed if the current is reversed.

The Scottish scientist William Thomson (later Lord Kelvin) discovered in 1854 that if a temperature difference exists between any two points of a current-carrying conductor, heat is either evolved or absorbed depending upon the material. (This heat is not the same as Joule heat, or I²R heat, which is always evolved.) If such a circuit absorbs heat, then heat may be evolved if the direction of the current or of the temperature gradient is reversed.

It can be shown that the Seebeck effect is a result of the combined Peltier and Thomson effects. Magnetic fields have been shown to influence all these effects. Many devices based on thermoelectric effects are used to measure temperature, transfer heat, or generate electricity.

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 Scott Meenen