An ideal black body is:
Correct answer: D. All of the above
- A. The most efficient radiator
- B. A perfect absorber of radiation
- C. A body whose absorber power is unity
- D. All of the above
Explanation
A black body absorbs all incident radiation without reflecting or transmitting any of it. It emits radiation across a broad spectrum of frequencies based solely on its temperature. This emission follows Planck's law. The absorptivity of a black body is the same for all wavelengths and angles of incidence. The emitted radiation spectrum is continuous and depends on the temperature of the black body. Warmer black bodies emit more radiation, and the peak of the emission shifts to shorter wavelengths with increasing temperature. The intensity (brightness) of radiation emitted by a black body is directly proportional to the fourth power of its absolute temperature, as described by the Stefan-Boltzmann law. These characteristics are theoretical ideals, and while no real object perfectly meets these criteria, certain objects, like stars or specially designed cavities, can approximate the behavior of a black body under specific conditions.
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About Dawn of Modern Physics
Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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