Stefan-Boltzmann law

Stefan-Boltzmann law (also Stefan's law) states that the total energy radiated per unit surface area of a black body in unit time (black-body irradiance), (or the energy flux density (radiant flux) or the emissive power), j* is directly proportional to the fourth power of its thermodynamic temperature T:

Related Topics:
Energy - Black body - Irradiance - Energy flux density - Flux - Emissive power - Proportional - Thermodynamic temperature

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: j^{star} = sigma T^{4}

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The non-fundamental constant of proportionality is called the Stefan-Boltzmann constant or the Stefan's constant σ. Its value is

Related Topics:
Constant of proportionality - Stefan-Boltzmann constant

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:

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sigma=rac{2pi^5 k^4}{15c^2h^3}= 5.670 400(40) imes 10^{-8} extrm{J,s}^{-1} extrm{m}^{-2} extrm{K}^{-4}.

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Thus at 100 K the energy flux density is 5.67 W/m2, at 1000 K 56.7 kW/m2, etc.

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The law was experimentally discovered by Jožef Stefan (1835-1893) in 1879 and theoretically derived in the frame of the thermodynamics by Ludwig Boltzmann (1844-1906) in 1884. Boltzmann treated a certain ideal heat engine with the light as a working matter instead of the gas. This law is the only physical law of nature named after a Slovene physicist. The law is valid only for ideal black objects, the perfect radiators, called blackbodies. Stefan published this law on March 20 in the article Über die Beziehung zwischen der Wärmestrahlung und der Temperatur (On the relationship between thermal radiation and temperature) in the Bulletins from the sessions of the Vienna Academy of Sciences.

Related Topics:
Jožef Stefan - 1835 - 1893 - 1879 - Thermodynamics - Ludwig Boltzmann - 1844 - 1906 - 1884 - Heat engine - Light - Slovene - Physicist - March 20

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