What is black? - The popular science article

by:FOT     2020-11-21
What is black? ( 1) In any condition, fully absorbed any wavelength of incoming radiation without any reflection of the object. ( 2) Absorption ratio is 1. ( 3) At any temperature, for any wavelength of incident radiation absorbing all objects. Any object with radiation, absorption and emission of electromagnetic waves. Radiation of electromagnetic wave in each band is different, have certain spectral distribution. The spectral distribution is related to the characteristics of the object itself and its temperature, thus is called thermal radiation. In order to study does not depend on material thermal radiation law of specific property, physicists defines an ideal object - — Blackbody ( 黑体) As a thermal radiation research objects. Blackbody refers to the incident electromagnetic wave is absorbed entirely, no reflection, no transmission ( Of course, radiation blackbody radiation but still want to) 。 Kirchhoff's law of radiation ( Kirchhoff) , in thermal equilibrium state of the object by the ratio of the radiation energy and absorption rate has nothing to do with the physical properties of the object itself, is only related to the wavelength and temperature. According to the kirchhoff's law of radiation under a certain temperature, is inevitably blackbody radiation, etc. the largest object can be called a perfect radiator. Radiate different substance in the infrared thermal imaging of the electromagnetic wave is never intersect, the blackbody is only a reference, the equivalent of a zero. But in the real world there is no such ideal blackbody, so what used to depict the difference? For any wavelength and define the emissivity for the wavelength of a tiny wavelength interval, the real object of radiation energy and the ratio of the blackbody radiation energy under same temperature. Apparently emissivity for positive number between 0 and 1, average emission rate depends on the material characteristics, environmental factors and the observation conditions. If emission rate has nothing to do with the wavelength, the object is called gray body ( 灰色的身体) , otherwise called selective radiator. Infrared thermal imager in the process of long-term use will be influenced by external factors, and cause error, so you need to use boldface to calibration.
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