black body

(noun)

An idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. Although black body is a theoretical concept, you can find approximate realizations of black body in nature.

Related Terms

Examples of black body in the following topics:

  • Planck's Quantum Hypothesis and Black Body Radiation

    • A black body emits radiation called black body radiation.
    • A black body in thermal equilibrium (i.e. at a constant temperature) emits electromagnetic radiation called black body radiation.
    • This equation explains the black body spectra shown below.
    • Typical spectrum from a black body at different temperatures (shown in blue, green and red curves).
    • Identify assumption made by Max Planck to describe the electromagnetic radiation emitted by a black body

  • Infrared Waves

    • Mid-infrared, from 30 to 120 THz (10 to 2.5 μm) - Hot objects (black-body radiators) can radiate strongly in this range, and human skin at normal body temperature radiates strongly at the lower end of this region.
    • Objects at room temperature will emit radiation mostly concentrated in the 8 to 25 µm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see sections on black body radiation and Wien's displacement law).
    • This is a property of a surface which describes how its thermal emissions deviate from the ideal of a black body.

  • Energy and Momentum

    • Planck theorized that "black bodies" (thermal radiators) and other forms of electromagnetic radiation existed not as spectra, but in discrete, "quantized" form.

  • Energy, Mass, and Momentum of Photon

    • Max Planck explained black body radiation using semiclassical models, in which light is still described by Maxwell's equations, but the material objects that emit and absorb light, do so in amounts of energy that are quantized.

  • Basic Assumptions of the Bohr Model

    • We have seen that Planck adopted a new condition of energy quantization to explain the black body radiation, where he introduced the Planck constant $h$ for the first time.

  • Particle-Wave Duality

    • Black body radiation: In 1901, to explain the observed spectrum of light emitted by a glowing object, Max Planck assumed that the energy of the radiation in the cavity was quantized, contradicting the established belief that electromagnetic radiation is a wave.

  • The Photoelectric Effect

    • Building on Max Planck's theory of black body radiation, Einstein theorized that the energy in each quantum of light was equal to the frequency multiplied by a constant $h$, later called Planck's constant.

  • Diffraction Revisited

    • From the work by Planck (black body radiation) and Einstein (photoelectric effect), physicists understood that electromagnetic waves sometimes behaved like particles.

  • Radiation

    • The hot body emits electromagnetic waves that are absorbed by our skin, and no medium is required for them to propagate.
    • Black is the most effective, and white the least.
    • People living in hot climates generally avoid wearing black clothing, for instance.
    • Similarly, black asphalt in a parking lot will be hotter than the adjacent gray sidewalk on a summer day, because black absorbs better than gray.
    • The reverse is also true—black radiates better than gray.

  • The Coriolois Force

    • The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame.
    • In the inertial frame of reference (upper part of the picture), the black object moves in a straight line.