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| {{Thermoelectric effect|cTopic=Principles}}
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| The '''Ettingshausen Effect''' (named for [[Albert von Ettingshausen]]) is a [[thermoelectric effect|thermoelectric]] (or thermomagnetic) phenomenon that affects the [[electric current]] in a conductor when a [[magnetic field]] is present.<ref name=ettinghausen86>{{cite journal|last=v. Ettingshausen|first=A.|coauthors=Nernst, W.|title=Ueber das Auftreten electromotorischer Kräfte in Metallplatten, welche von einem Wärmestrome durchflossen werden und sich im magnetischen Felde befinden|journal=Annalen der Physik und Chemie|year=1886|volume=265|issue=10|pages=343–347|doi=10.1002/andp.18862651010|url=http://dx.doi.org/10.1002/andp.18862651010|accessdate=23 February 2012|bibcode = 1886AnP...265..343E }}</ref>
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| Ettingshausen and his PhD student [[Walther Nernst]] were studying the [[Hall effect]] in [[bismuth]], and noticed an unexpected perpendicular current flow when one side of the sample was heated. This is also known as the [[Nernst effect]]. Conversely, when applying a current (along the y-axis) and a perpendicular magnetic field (along the z-axis) a temperature gradient appears along the x-axis. Because of the Hall effect, electrons are forced to move perpendicular to the applied current. Due to the accumulation of electrons on one side of the sample, the number of collisions increases and a heating of the material occurs.
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| This effect is quantified by the Ettingshausen coefficient ''P'', which is defined as:
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| ::<math>P=\frac{dT/dx\cdot d_z}{|B_z|\cdot I_y}</math>
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| where ''dT/dx'' is the temperature gradient that results from the ''y''-component ''I<sub>y</sub>'' of an electric current and the ''z''-component ''B<sub>z</sub>'' of a magnetic field. It also depends on the thickness ''d<sub>z</sub>'' of the material because the total heat flow will depend on its cross section for the temperature gradient. P is independent of the sample width because the total Hall voltage will be constant, as will the total drop in T.
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| [[File:Sketch of Ettingshausen effect.svg|thumb|temperature gradient due to Ettingshausen effect with applied magnetic field and electric current]]
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| In most metals like [[copper]], [[silver]] and [[gold]] ''P'' is on the order of {{val|e=-16|u=K/TA}} and thus difficult to observe in common magnetic fields. In [[bismuth]] the Ettingshausen coefficient is several orders of magnitude larger because of its poor [[thermal conductivity]].
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| ::<math>P_{\mathrm{bismuth}}=7.5\pm0.3\times 10^{-4}\frac{K}{T\cdot A}</math><ref name=tbmtfb2002>{{cite web|title=ettingshausen effect in bismuth|url=http://www.bubek.org/physics/pp_stuff/ettinghauseneffekt.pdf|accessdate=3 May 2012}}</ref>
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| ==See also==
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| *[[Hall effect]]
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| ==References==
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| {{Reflist}}
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| [[Category:Thermodynamics]]
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| [[Category:Electrodynamics]]
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Latest revision as of 13:11, 28 October 2014
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