Stefan's law


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Stefan's law

(steff -ănz) (Stefan-Boltzmann law) The law relating the total energy, E , emitted over all wavelengths, per second, per unit area of a black body, with the temperature, T , of the body:
E = σT 4

σ is Stefan's constant, which has the value 5.6705 × 10–8 W m–2 K–4. The law can be derived from Planck's radiation law (see black body), but was first deduced by Josef Stefan in 1879 and then derived from thermodynamics by Ludwig Boltzmann in 1884. See also luminosity.

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Extrapolations from Stefan's law of the proportionality of total radiation from a black body to the fourth power of the absolute temperature, are therefore not certainly applicable to the problem, even though the law has been verified through a range of some hundreds of degrees" [20].
It is known that the emissivity of gases can fall with temperature in clear violation of Stefan's law [24].
On the temperature of the photosphere: energy partition in the Sun
In some climate models [5, 6], the radiation which the Earth emits is deduced by applying Stefan's law [12], at a given effective temperature, thereby treating the globe as a uniform blackbody source.
Note, in this regard, that Stefan's law invokes a 4th power temperature dependence [12].
Global warming and the microwave background
This is known as Stefan's law of emission ([epsilon] = [sigma][T.sup.4]), where [epsilon] represents total emission and Stefan's constant, [sigma], is equal to 5.67051 x [10.sup.-8] Watts/([m.sup.2][K.sup.4]) [12].
Consequently, we can see that Stefan's law does not hold for gases [7].
The little heat engine: heat transfer in solids, liquids and gases

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