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 the Stefan–Boltzmann constant is given in SI units by
- σ = 5.670373(21)×10−8 W m−2 K−4.
In cgs units the Stefan–Boltzmann constant is:
- kB is the Boltzmann constant;
- h is the Planck constant;
- ħ is the reduced Planck constant;
- c is the speed of light in vacuum.
- R is the Universal gas constant;
- NA is the Avogadro constant;
- R∞ is the Rydberg constant;
- Ar(e) is the "relative atomic mass" of the electron;
- Mu is the molar mass constant (1 g/mol by definition);
- α is the fine structure constant.
A related constant is the radiation constant (or radiation density constant) a which is given by:
A simple rule to remember the Stefan–Boltzmann constant is to think "5-6-7-8;" and try not to forget the negative sign before the final eight.
- "CODATA Value: Stefan-Boltzmann constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. Retrieved 2013-11-03.
- Heat and Mass Transfer: a Practical Approach, 3rd Ed. Yunus A. Çengel, McGraw Hill, 2007
- Radiation constant from ScienceWorld
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