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The temperature of a system in classical thermodynamics is intimately related to the zeroth law of thermodynamics; two systems having to have the same temperature if they are to be in thermal equilibrium (i.e. there is no net heat flow between them). However, it is most useful to have a temperature scale. By making use of the ideal gas law one can define an absolute temperature

T = \frac{pV}{Nk_B}

however, perhaps a better definition of temperature is

\frac{1}{T(E,V,N)} = \left. \frac{\partial S}{\partial E}\right\vert_{V,N}

where S is the entropy.


Temperature has the SI units of kelvin (K) (named in honour of William Thomson) The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

External links

Kinetic temperature

T = \frac{2}{3} \frac{1}{k_B} \overline {\left(\frac{1}{2}m_i v_i^2\right)}

where k_B is the Boltzmann constant. The kinematic temperature so defined is related to the equipartition theorem; for more details, see Configuration integral.

Configurational temperature

Non-equilibrium temperature

Inverse temperature

It is frequently convenient to define a so-called inverse temperature, \beta, such that

\beta := \frac{1}{k_BT}

See also


  1. William Thomson "On an Absolute Thermometric Scale, founded on Carnot's Theory of the Motive Power of Heat, and calculated from the Results of Regnault's Experiments on the Pressure and Latent Heat of Steam", Philosophical Magazine October pp. (1848)
  2. H. Preston-Thomas "The International Temperature Scale of 1990 (ITS-90)", Metrologia 27 pp. 3-10 (1990)
  3. H. Preston-Thomas "ERRATUM: The International Temperature Scale of 1990 (ITS-90)", Metrologia 27 p. 107 (1990)