Thermoelectricity

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Thermoelectricity is the conversion from temperature differentials to electricity or vice versa.

It is accomplished in one of several ways:

The Peltier-Seebeck effect
Thermionic emission
Indirectly through magnetohydrodynamics (see Rubidium).

The conducting material is not limited to solids with electrons as charge carriers. Such effects can be observed in conductors where the carriers are ions, or in semiconductors where the carriers are holes or electrons.

It is the principle behind heat engines, heat pumps, thermocouples, thermal diodes, and solid-state refrigerators, etc.

It can be used to electrically measure temperature, or to generate electric power from a heat source.

The heat from radioactive decay has been used to electrically power several space probes, in the form of radioisotope thermoelectric generators.

Thermoelectric power sometimes refers to this direct conversion, but usually just refers to a power plant which converts heat into electricity, through the use of steam turbines or similar devices.

[edit] Batteryless radio

Thermoelectricity was widely used in the remote parts of the Soviet Union from the 1920s to power radios. The equipment comprised some bi-metal rods, one end of which could be inserted into the fireplace to get hot with the other end left out in the cold.

Another way of achieving the same function is a Clockwork radio.