Thermoelectricity

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Thermoelectricity, in physics, electricity generated by the application of heat to the junction of two dissimilar materials. If two wires of different materials are joined at their ends and one end is maintained at a higher temperature than the other, a voltage difference will arise, and an electric current will exist between the hot and the cold junctions. This phenomenon was first observed in 1821 by the German physicist Thomas Seebeck and is known as the Seebeck effect.

For a given combination of materials, the voltage difference varies in direct proportion to the temperature difference. This phenomenon can be utilized for the accurate measurement of temperature by means of a thermocouple in which one wire junction is maintained at a known reference temperature (for example, in an ice bath) and the other at the location where the temperature is to be measured. At moderate temperatures (up to about 260° C/500° F), wire combinations of iron and copper, iron and constantan (a copper-nickel alloy), and copper and constantan are frequently used. At high temperatures (up to 1649° C/3000° F), wires made from platinum and a platinum-rhodium alloy are employed. Because thermocouple wires can be made very small, they also provide a means for the accurate measurement of local spot temperatures. The current can be increased by using semiconductors instead of metals, and a few watts of power can be produced at efficiencies of up to 6 percent (Transistor).

The inverse effect occurs if current is sent through a circuit made of dissimilar materials, the junctions of which are at the same temperature. In this case, heat will be absorbed at one junction and given up at the other. This phenomenon is known as the Peltier effect for the French physicist Jean Peltier, who discovered it in 1834. Semiconductor systems operating on the Peltier effect can be used as low-powered miniaturized refrigerators for special applications.

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