Any object, as long as its temperature is above absolute zero, emits radiation to the surrounding, which is called temperature radiation.As long as its temperature is above absolute zero, it will also absorb radiant energy from the outside.
As early as 1859, German physicistKirchhoffOn the basis of summarizing the experimental findings at that time, the general law of thermal radiation of all objects is obtained by theoretical methods: under the same temperature, the monochromatic radiation emittance Mi (λ, T) of each radiation source is proportional to the monochromatic absorption rate α i (λ, T), and its ratio is the same for all radiation sources (i=1, 2, ∨), which is only determined bywavelengthλ and temperature TUniversal function。The black object strongly absorbs the visible light energy, so when obtaining energy, it should also have strong radiation in the visible light area, so the black objectBlackbody radiationResearch from the perspective of to determine universalityfunctionThe specific form of is extremely attractive.Obviously, if the monochromatic absorptivity α i (λ, T)=1, thenradiation sourceMonochrome ofRadianceMi (λ, T) is the universal function to be studied.The radiator with α i (λ, T)=1 is the absolute black body, which is called black body for short.The radiation brightness of the black body is the same in all directions, that is, the black body is a complete cosine radiator, with less radiation capacity than the black body, but the temperature radiator with the same spectral distribution of radiation as the black body is called gray body.
Any object, as long as its temperature is above absolute zero, emits radiation to the surrounding, which is called temperature radiation;As long as its temperature is above absolute zero, it will also absorb radiant energy from the outside.Objects at different temperatures and environments areelectromagnetic radiationThe form emits energy, and the blackbody is a complete temperature radiator, that is, the radiation flux emitted by any non blackbody is less than the radiation flux emitted by the blackbody at the same temperature;Moreover, the radiation ability of non blackbody is not only related to temperature, but also related to the properties of surface materials, while the radiation ability of blackbody is only related to temperature.In the blackbody radiation, there are electromagnetic waves of various wavelengths, and the energy distribution according to the wavelength is related to the temperature of the blackbody.
In 1900, there was a long-term study of thermodynamicsGermanyphysical scientistPlonkCombining the Venn formula and Rayleigh Jones formula, using the interpolation method, a constant of its own is introduced, and the result is a formula, which is precisely consistent with the experimental results. It is Planck's formula, namely Planck's radiation law.This law is expressed in spectral radiance.
First radiation constantC1 =2πhctwo= 3.74×10-16(W × mtwo）
The second radiation constant C2=hc/K=1.4398 × 10-2(m × Kelvin)
K-Boltzmann constant
Curve of spectral brightness of blackbody changing with wavelength.The absolute temperature of the blackbody is marked on each curve.The diagonal straight line intersecting the maximum values of the curves represents the Wien displacement line.
Wien's displacement law
The wavelength λ of the maximum spectral brightness is inversely proportional to its absolute temperature T: λmax=A/T
A is a constant, that isVenn constant，A=2.896×10-3(m × Kelvin)
L max=4.10T5 ´ 10-6 (Watt/m 3. Spherical angle. Kelvin 5)
With the increase of temperature, the wavelength of the maximum absolute blackbody spectral brightness moves to the short wave direction.
