Black Body Radiation
It's a quantam mechanic effect that is absorbed. When a radiant energy falls on the surface of any body, some part of it is reflected, some part is absorbed and the rest part is transmitted. The whole of the energy is not absorbed because generally the surface of ordinary bodies are not perfect absorbers of radiation. However, if the radiant energy is allowed to fall on the black metallic surface, it is found that the energy is almost completely absorbed. A body which completlyc absorbs the radiant energy falling on it is called a perfect black body.
The absorption is found to be more perfect if we take a hollow sphere blackned on the inside and having a small hole for the entry of the radiation. This is so because any radiant that enter through the hole is reflected over and the again by the walls of the sphere till finally it is completely absorbed. Here is a commonly used black body
With the increase in temperature, the energy radiant per unit area per unit time from any surface increases rapidly and simultaneously the colour changes from dull red through cherry red and orange up to a bright white heat. Further, it is observed that at the same temperature , the rate of energy emission is much less than a bright metal like platinum than for a dull black surface such as an incandescent carbon filament.
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