black body

Also found in: Dictionary, Thesaurus, Medical, Legal, Wikipedia.
Related to black body: Black body radiation
Black-body radiation curves for different temperaturesclick for a larger image
Black-body radiation curves for different temperatures

black body

A body that absorbs all the radiation falling on it, i.e. a body that has no reflecting power. It is also a perfect emitter of radiation. The concept of a black body is a hypothetical ideal. The radiation from stars, and their effective and color temperatures, can however be described by assuming that they are black bodies.

Black-body radiation is the thermal radiation (see thermal emission) that would be emitted from a black body at a particular temperature. It has a continuous distribution of wavelengths. The graph of the energy, or intensity, of the radiation has a characteristic shape (see illustration) with a maximum value at a given wavelength, λmax. At lower temperatures the black-body radiation is mainly in the infrared region of the spectrum. As the temperature increases the maximum of the curve moves to shorter wavelengths. Curves at different temperatures follow the relationship

λmax T = 2.9 × 103

where the wavelength is measured in micrometers. This is known as the Wien displacement law. The radiation from a hot black body is greater at every wavelength than the radiation from a cooler black body. The total radiation flux thus increases rapidly with increasing temperature, as described by Stefan's law.

Stefan's law gives the total energy emitted over all wavelengths per second per unit area of a black body. The energy emitted at a particular wavelength by a black body can be predicted from Planck's radiation law. This law was derived by Max Planck from his quantum theory, propounded in 1900. If E (λ,T) is the energy emitted per unit wavelength interval at wavelength λ, per second, per unit area, into unit solid angle, by a body at thermodynamic temperature T , then

E (λ,T) = (2πhc 25)[ehc kT – 1]–1

h is the Planck constant, k the Boltzmann constant, and c the speed of light. Stefan's law and the Wien displacement law can both be derived from Planck's law.

Planck's radiation law describes only the continuous spectrum emitted by a black body. The continuous radiation from a star, as opposed to a black body, does not usually follow Planck's law exactly, although over a broad region of the spectrum the law is a good approximation.

References in periodicals archive ?
Starting with the special case of a black body, Robitaille, Kirchhoff and Planck all agree that the radiation is necessarily black.
Using this knowledge, one measuring point of the processing program evaluates the temperature of the black body with a dedicated e of 1 (Figure 6).
Whitney also raises very important questions regarding the mutually reinforcing aspects of racism, horror and the Black body as a site of phobia.
It is therefore relevant to understand how and why Black Pete, "once a liminal figure of fertility and winter angst" (Smith 2014:228), became portrayed as a black body, including prominent phenotypical features like a solid black skin color, thick bright red lips, and curly or wooly dark hair.
Embedded within the history of European and Anglo-American racism, profiling the Black body within a Manichean divide, where Blackness signifies "evil" and whiteness signifies "good," bespeaks a toxic metanarrative that is not exclusively ingrained in whites in terms of the egregious ways in which they profile Black male bodies.
But in the universality of its presence and its unequal power relations with the white, the black body cuts across continents.
In Western societies, the black body carries tremendous signifying power; it is often allowed to stand in for individuals, thus overshadowing the actual person.
The all black ADH2047 comes with a black body and black bezel whereas the ADH2031 and ADH2032 feature polished silver & gold bezels.
He was wearing a black ski mask, white top under a black body warmer with a white motif on the left breast, dark blue tracksuit trousers with a white motif on the thigh.
Remember the black body bags, remains of a stroller, a notebook, Nazi numbers tattoed on burned arms, bits of jewelry, military berets, officers' insignia.
Burlesque star Christina lived up to her role in that movie by sparkling in a black body suit with a silver Swarovski-covered belt.
A continuation pattern with a long, black body followed by another black body that has gapped below the first one.