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Black-body radiation is the thermal electromagnetic radiation ... The emissivity of a material specifies how well a real body radiates energy as compared with a black ...
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation emitted by a black body in thermal equilibrium with its environment is called black-body radiation. The name "black body" is given because it absorbs all colors of light.
A so-called grey body is a body for which the spectral emissivity is independent of wavelength, so that the total emissivity, , is a constant. [ 3 ] : 71 In the more general (and realistic) case, the spectral emissivity depends on wavelength.
Emissivity of a body at a given temperature is the ratio of the total emissive power of a body to the total emissive power of a perfectly black body at that temperature. Following Planck's law , the total energy radiated increases with temperature while the peak of the emission spectrum shifts to shorter wavelengths.
The table on the right shows how the radiation of a black body at this temperature is partitioned, and also how sunlight is partitioned for comparison. Also for comparison a planet modeled as a black body is shown, radiating at a nominal 288 K (15 °C) as a representative value of the Earth's highly variable temperature.
Independent of the condition of thermal equilibrium, the emissivity of the wall is defined as the ratio of emitted energy to the amount that would be radiated if the wall were a perfect black body. The emitted energy is thus ε λ E b λ ( λ , T ) {\displaystyle \varepsilon _{\lambda }E_{b\lambda }(\lambda ,T)} where ε λ {\displaystyle ...
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. [1] [2] Effective temperature is often used as an estimate of a body's surface temperature when the body's emissivity curve (as a function of wavelength) is not known.
The ratio of any body's emission relative to that of a black body is the body's emissivity, so a black body has an emissivity of one. Absorptivity, reflectivity , and emissivity of all bodies are dependent on the wavelength of the radiation.