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Perfect Blackbody

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Estimated time: 3 minutes
  • Ferry’s Blackbody
Maharashtra State Board: Class 11

Definition: Perfect Black Body

A body which absorbs the entire radiant energy incident on it, neither reflecting nor transmitting any radiation, so that its absorptance is unity (a = 1, t = 0, r = 0), and which appears black in light and glows in the dark because a good absorber is always a good emitter, is called a perfectly black body.

Maharashtra State Board: Class 11

Key Points: Properties of a Perfect Black Body

  • A perfectly black body absorbs completely the radiations of all wavelengths incident on it — it neither reflects nor transmits any radiation, hence a = 1.
  • The colour of an opaque body is the colour (wavelength) of radiation reflected by it. Since a black body reflects no wavelength, it appears black whatever be the colour of radiations incident on it.
  • In practice, Ferry's body is considered a perfect black body — the lampblack used in it absorbs 97% of incident energy.
  • A perfect black body appears black in light and glows in the dark, because a good absorber is always a good emitter of thermal radiation.
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