ثابت ستيفان-بولتزمان
ثابت ستيفان-بولتزمان (بالإنگليزية: Stefan–Boltzmann constant) هوثابت فيزيائي وهوثابت التناسب في قانون ستيفان - بولتزمان.
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:
In thermochemistry the Stefan–Boltzmann constant is often expressed in cal cm-2day-1K-4:
In US customary units the Stefan–Boltzmann constant is:
The value of the Stefan–Boltzmann constant is derivable as well as experimentally determinable; see Stefan–Boltzmann law for details. It can be defined in terms of the Boltzmann constant as:
where:
- kB is the Boltzmann constant;
- h is the Planck constant;
- ħ is the reduced Planck constant;
- c is the speed of light in vacuum.
The CODATA recommended value is calculated from the measured value of the gas constant:
where:
- 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.
.. الصيغة ذات الأبعاد : [ M 1 L 0 T -3 K -4]
A related constant is the radiation constant (or radiation density constant) a which is given by:
الهامش
-
^ "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. External link in
|work=(help) - ^ Heat and Mass Transfer: a Practical Approach, 3rd Ed. Yunus A. Çengel, McGraw Hill, 2007
- ^ Radiation constant from ScienceWorld
