- Stefan–Boltzmann law
▪ physicsstatement that the total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature. Formulated in 1879 by Austrian physicist Josef Stefan (Stefan, Josef) as a result of his experimental studies, the same law was derived in 1889 by Austrian physicist Ludwig Boltzmann (Boltzmann, Ludwig Eduard) from thermodynamic considerations: if E is the radiant heat energy emitted from a unit area in one second and T is the absolute temperature (in degrees kelvin), then E = σT4, the Greek letter sigma (σ) representing the constant of proportionality, called the Stefan–Boltzmann constant. This constant has the value 5.6704 × 10−8 watt per metre2∙K4. The law applies only to blackbodies (blackbody), theoretical surfaces that absorb all incident heat radiation.
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