black body

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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 ?
Simply put, Aibileen's reflections expose Stockett's own anxieties regarding black women's sexuality and fertility because the black bodies of Aibileen and Minny function as the vehicles by which Stockett conveniently regulates and assails black female sexuality.
Through an analysis of first-person testimonials by musician Questlove, she shows just how processes of quantification minimalize the voices of Black bodies that actually suffer.
Martinique-born, French-Algerian psychiatrist Frantz Fanon, discusses the negative connotation of the "color" black and its application to black bodies in his 1952 work Black Skin, White Masks (Fanon [2008]:146):
Johnson and his son, and the bodies of Black males, more generally, were/are faced with confronting white covenants that stipulate that Black "presence is unwelcome." Black bodies, then, are transgressive in virtue of being Black, one might argue in virtue of being.
Although above I point to the middle passage as the matrix in terms of which black identity is shaped, we must be cognizant of how black identity and black subjectivity can be erroneously tethered to that moment in time and physical space, (3) which then raises the issue of how a specific black historical narrative can function monolithically and thus exclude those black bodies that don't narrativize the middle passage in the same way or even at all.
observes that Christian faith often has not functioned to prevent the continual objectification of black bodies. To help rectify the situation, she appeals to womanist theologies to articulate the norms necessary to critique white European and North American Christian anthropological thinking about black bodies (50).
A bearish reversal pattern consisting of three consecutive long black bodies where each day closes at or near its low and opens within the body of the previous day.
This same racialized understanding of black bodies, which lead to incompetent medical care, was also responsible for black soldiers needing such care.
The World Museum's Bug House has eight Indian Ground Beetles, more commonly known as domino beetles because of the white spots on their black bodies.
The World Museum's Bug House has eight Indian Ground Beetles, more commonly known as domino beetles, because of the white spots on their black bodies.
Among the achievements they describe are investigations of the spectral distributions of the emission of black bodies that laid the experimental foundation for Max Planck's 1900 radiation law, the discovery of the Meissner effect in superconductors, the discovery of the element rhenium, and contributions to knowledge about radioactivity.
She also describes how the differential death rates were used, with the exception of some doctors, to construct narratives concerning the inherent inferiority of black bodies.

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