Seebeck effect


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thermoelectricity

thermoelectricity, direct conversion of heat into electric energy, or vice versa. The term is generally restricted to the irreversible conversion of electricity into heat described by the English physicist James P. Joule and to three reversible effects named for Seebeck, Peltier, and Thomson, their respective discoverers. According to Joule's law, a conductor carrying a current generates heat at a rate proportional to the product of the resistance (R) of the conductor and the square of the current (I). The German physicist Thomas J. Seebeck discovered in the 1820s that if a closed loop is formed by joining the ends of two strips of dissimilar metals and the two junctions of the metals are at different temperatures, an electromotive force, or voltage, arises that is proportional to the temperature difference between the junctions. A circuit of this type is called a thermocouple; a number of thermocouples connected in series is called a thermopile. 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 heat is absorbed by such a circuit, 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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Seebeck effect

The generation of a temperature-dependent electromotive force (emf) at the junction of two dissimilar metals. This phenomenon provides the physical basis for the thermocouple. In 1821, T. J. Seebeck discovered that near a closed circuit composed of two linear conductors of two different metals a magnetic needle would be deflected if, and only if, the two junctions were at different temperatures, and that if the temperatures of the two junctions were reversed the direction of deflection would also be reversed. He investigated 35 different metals and arranged them in a series such that at a hot junction, current flows from a metal earlier in the series to a later one. See Electromotive force (emf)

A thermocouple consists of a pair of wires of dissimilar metals, joined at the ends. One junction is kept at an accurately known cold temperature, usually that of melting ice, and the other is used for the measurement of an unknown temperature, by measuring the emf generated as a result of the Seebeck effect. See Thermocouple, Thermoelectricity

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

Seebeck effect

[′zā‚bek i‚fekt]
(electronics)
The development of a voltage due to differences in temperature between two junctions of dissimilar metals in the same circuit.
(graphic arts)
A photographic emulsion that is exposed until a faint visible image appears, and is then exposed to colored light and takes on the color of the light to which it is exposed.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The thermoelectric cooling phenomenon is physically based on the Peltier effect, which was discovered by Jean Peltier in 1834-13 years after the Seebeck effect was unveiled (10).
Thermoelectric [TE] devices harvest energy developed from temperature differences via the Seebeck effect, i.e., a temperature difference at the junction of two metals or semiconductors causes current to flow across the junction.
His life and work, particularily the discovery of the thermoelectric effect (the Seebeck effect), is described by Enn Velmre in the first paper of this issue.
Wireless Industrial Technologies, an Oakland, Calif., company cofounded by Wright, uses energy scavengers that take advantage of the Seebeck effect, in which certain metals develop voltages when one end is hotter than the other.
The thermoelectric (TE) phenomena can provide the direct conversion of applied temperature gradient into electricity (the Seebeck effect) or electricity into temperature difference (the Peltier effect).
It may be that the magnetothermopower from polycrystalline [Sr.sub.2-x][La.x]FeMo[O.sub.6] and [Ba.sub.2]FeMo[O.sub.6] arises from a spin- dependent Seebeck effect. This type of magnetothermopower has been reported in magnetic tunneling junctions where one or more of the layers are ferromagnetically ordered and display electronic spin polarization [16, 17].
We call the first phenomenon the Seebeck effect, where electrical voltage is developed when there is a gradient of temperature between the terminals and was discovered by Seebeck in 1821 while the second is just converse effect of the first one and it was discovered by Peltier in 1834 [1].
All low-level signals are subject to thermally induced voltage offsets based on the Seebeck effect. A junction of dissimilar metals, such as found in reed relays, produces a small voltage when a temperature gradient exists along the length of the conductors.
Theoretical researches demonstrated that ultrafast photoresponse processes should be attributed to anisotropy diffusion and Seebeck effect. Researches also demonstrated that the concentrations of lanthanide of the samples could modulate the photoresponse signals in nanometer size domain tilted thin films, which indicate a new type nanometer scale photosensitive source.