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 ?
Two-hundred black body bags lined up on Brighton beach in East Sussex by campaigners highlighting Britain's 'shameful' response to the migrant crisis in the Mediterranean Tom
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.
By emphasizing the black body as a sexual deviant within the white imagination, there is a sense that these bodies are ignorant and animalistic, thus needing to be contained and enslaved.
A continuation pattern with a long, black body followed by another black body that has gapped below the first one.
Moreover, held hostage to nineteenth century views of the black body, it is equally unlikely that the Union would have or could have offered African American soldiers' first rate treatment, for such treatment remained elusive for white soldiers.
Xicato's Corrected Cold Phosphor Technology ensures that color points centered on the Black Body Locus for a natural light are maintained to a two-step MacAdam ellipse tolerance, part to part and through life.
Contributors here explore how the black body is used in literature and visual representations generally to define and defend certain images about what the US is or should be.
Yellow and blue lines shimmer along the black body of Chelidonura hirundinina, but what the researchers find even more beautiful is a little fold of skin lined with hairs that guide blobs of sperm from a worm's testes along a brief trip in the outside world to its penis.
Flitting from leafy branch to branch on towering trees in Newhall Park, the painted redstart flashed cherry red feathers hidden under the wings of its jet black body.
Black Body is an exploration of the changing meaning of women's blackness in relation to nation.
In Black Style, Carol Tulloch, a senior research fellow in Black Visual Culture at Chelsea College of Art in London, England, writes, "The contributions presented in Black Style also expose the complexities and 'ongoing redefinition' of what it means to be 'black' through the black body and how it is dressed.