Thermopower
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The thermopower, thermoelectric power, or Seebeck coefficient of a material describes how it functions thermoelectrically.
The Seebeck coefficients, represented as <math>S<math>, are non-linear, and depend on the conductors' absolute temperature, material, and molecular structure.
If the temperature difference between the two nodes of a thermocouple is small,
- <math>
T_2 = T_1 + \Delta T \, <math>
and a voltage ΔV is seen at the terminals, then the thermopower of the entire thermocouple is defined as:
- <math>
S_{AB} = S_B-S_A = \lim_{\Delta T \to 0} {\Delta V \over \Delta T} <math>
This can also be written in relation to the electric field <math>E<math> and the temperature gradient <math>\nabla T<math>, by the equation
- <math>
S = {E \over \left | \nabla T \right |} <math>
Superconductors have zero thermopower, and can be used to make thermocouples. This allows a direct measurement of the thermopower of the other material, since it is the thermopower of the entire thermocouple as well. In addition, a measurement of the Thompson coefficient, <math>\mu<math>, of a material can also yield the thermopower through the relation: <math>S = \int {\mu \over T} dT<math>
In semiconductors the sign of the thermopower is used to determine whether the charge carriers are electrons or holes.