Stefan–Boltzmann constant

Stefan–Boltzmann constant

The Stefan–Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter σ, is the constant of proportionality in the Stefan–Boltzmann law: the total energy radiated per unit surface area of a black body in unit time is proportional to the fourth power of the thermodynamic temperature.

The value of σ is 5.670400e|−8 W·m-2·K-4. This value is derivable as well as experimentally determinable; see Stefan–Boltzmann law.

σ can be defined in terms of the Boltzmann constant k_{mathrm B} as:

:sigma = frac{2pi^5k_{mathrm B}^4}{15h^3c^2} = frac{pi^2k_{mathrm B}^4}{60hbar^3c^2}

where "h" is Planck's constant, hbar = h/2piis Dirac's form of Planck's constant, and "c" is the speed of light in a vacuum.

A related constant is the radiation constant ( [http://scienceworld.wolfram.com/physics/RadiationConstant.html] ) which is equal to

:frac{4sigma}{c}.

External links

* [http://physics.nist.gov/cgi-bin/cuu/Value?eqsigma Stefan–Boltzmann constant] , value from CODATA.


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