AuthorBY- SUPRAJA G.S Just think about an object which takes as much as you give and emits as much as it has, amazing right, well that’s what a Black body is. Ideally, a Black body is a physical body that absorbs all incident electromagnetic radiation. It is a perfect emitter and a perfect absorber of thermal radiation. It neither reflects nor transmits but absorbs the entire radiation incident on it, so it is treated as an ideal radiation receiver. Now you might be wondering is it essential for the black body to black, well it doesn’t necessarily need to be black. And Will you believe me if I say it’s a common phenomenon i.e all the bodies are black body radiators, yes, all the bodies are cause all the bodies emit a certain amount of radiation, but the amount of radiation, and position in the spectrum depends on the object temperature as well its emissivity. Due to various constraints such as the absolute temperature and the properties of material composing a radiating body, we don’t have a perfect black body in nature. Lampblack is the nearest to a black body. It absorbs 96% of visible light; both absorptivity and emissivity of a perfectly black body are unity. Black body radiation sources: Some examples of blackbody radiators that emit visible light or whose radiation is used for other processes include electric heaters, incandescent light bulbs, stoves, the sun, the stars, night vision equipment, burglar alarms, warm-blooded animals, etc.
Typical blackbody radiations: ● A filament in the bulb radiates energy in the infrared regions, initially goes to red, then yellow, an almost white when fully energized. ● As the welding temperature of a piece of metal increases, it initially glows red, then orange, and the color continues changing until it becomes a bright, bluish cast. An object that is not very hot still emits radiation but in the infrared region. This is utilized in night vision equipment which is used to detect infrared radiation and convert this into a visible image. This allows the detection of warm-blooded animals and people at night. The blackbody radiation sources are available in three main categories, based on the temperature range. ● Low-temperature blackbody with a range of between -40 °C to +150 °C ● High temperature extended area blackbody - from ambient temperature up to +600 °C ● High-temperature cavity blackbody - from ambient temperature up to 1200 °C Applications: The black bodies are used for lighting, heating, security, thermal imaging, as well as testing and measurement applications. Also, to know the Human-body emissions, Temperature relation between a planet and its star, to find Effective temperature of Earth and in cosmology, etc. Since the intensity of the energy at any temperature and wavelength and can be determined using the Planck Law of radiation. A blackbody radiation source with a known temperature, or, whose temperature can be measured, is usually used for calibrating and testing the radiation thermometers.
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