The Ettingshausen effect (named for

Albert von Ettingshausen Albert von Ettingshausen (30 March 1850 – 9 June 1932) was an Austrian physicist. He was professor of physics at Graz University of Technology, where he also taught electrical engineering. Earlier he was an assistant to Ludwig Boltzmann at the U ...

) is a

thermoelectric The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when ...

(or thermomagnetic) phenomenon that affects the electric current in a conductor when a magnetic field is present. Ettingshausen and his PhD student Walther Nernst were studying the

Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was dis ...

bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...

, and noticed an unexpected perpendicular current flow when one side of the sample was heated. This is also known as the

Nernst effect In physics and chemistry, the Nernst effect (also termed first Nernst–Ettingshausen effect, after Walther Nernst and Albert von Ettingshausen) is a thermoelectric (or thermomagnetic) phenomenon observed when a sample allowing electrical conduct ...

. 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. This effect is quantified by the Ettingshausen coefficient ''P'', which is defined as: ::

P=\frac

where ''dT/dx'' is the temperature gradient that results from the ''y''-component ''J_y'' of an electric current density (in

A/m^2

) and the ''z''-component ''B_z'' of a magnetic field. Sketch of Ettingshausen effect

In most metals like

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

and

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...

''P'' is on the order of and thus difficult to observe in common magnetic fields. In

the Ettingshausen coefficient is several orders of magnitude larger because of its poor

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

. ::

P_=7.5\pm0.3\times 10^\frac

References

{{Reflist Walther Nernst Thermoelectricity Electrodynamics

See also

References