Construct · 1 fields · 2 citations

black-body radiation: a standalone construct

One name. One construct. A landmark on the map.

● anchor · a standalone construct Nearest construct by meaningStefan-Boltzmann lawcompare the meanings
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black-bodyradiation1 CONSTRUCTBlack-body radiationKIRCHHOFF · BLACK BODY

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Physics

The temperature-fixed radiation of an ideal absorber

Gustav Kirchhoff introduced the idea in 1860, proving that for a body in thermal equilibrium, meaning one whose temperature has settled and stopped changing, the ratio of the radiation it emits to the radiation it absorbs depends only on temperature and wavelength, and he named the idealized perfect absorber that also emits the maximum possible radiation a black body. Black-body radiation is the characteristic electromagnetic radiation such a body gives off: a smooth spectrum whose shape and total intensity are fixed by temperature alone, independent of the body's material or shape. Classical physics could not reproduce the measured spectrum, and Max Planck resolved the problem in 1901 with what became Planck's law by assuming that energy is emitted only in discrete packets, a hypothesis that opened quantum theory. The construct is a landmark because a single number, the temperature, fixes the entire spectrum, which is why it underlies work from the surface temperatures inferred for stars to the calibration of infrared thermometers and the measurement of the 2.7 K cosmic microwave background.[1][2]

Unit
Spectral radiance (radiated power per unit area, per unit solid angle, per unit wavelength or frequency), set by temperature
Recovery means
Not applicable
Measured by
Measured with a spectrometer or bolometer on the radiation leaving a heated cavity or aperture that closely approximates a perfect absorber, then fitted to Planck's law to recover the temperature

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Nearby constructs

radiation3 fields · 3 citationsjingle · one word, three physical and biological constructsquantization3 fields · 3 citationsjingle · one word, three constructstemperature4 fields · 4 citationsjingle · one word, four constructs

References

  1. Kirchhoff, G. (1860). Ueber das Verhältniss zwischen dem Emissionsvermögen und dem Absorptionsvermögen der Körper für Wärme und Licht. Annalen der Physik, 185(2), 275–301. https://doi.org/10.1002/andp.18601850205
  2. Planck, M. (1901). Ueber das Gesetz der Energieverteilung im Normalspectrum. Annalen der Physik, 309(3), 553–563. https://doi.org/10.1002/andp.19013090310

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