Yahoo Web Search

  1. Black-body radiation - Wikipedia

    en.wikipedia.org/wiki/Black-body_radiation

    Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body).

    • Black Body

      A black body or blackbody is an idealized physical body that...

    • Planck's Law

      A black-body is an idealised object which absorbs and emits...

  2. Blackbody radiation - Simple English Wikipedia, the free ...

    simple.wikipedia.org/wiki/Blackbody_radiation

    Blackbody radiation is radiation produced by heated objects, particularly from a blackbody. A blackbody is an object that absorbs all radiation (visible light, infrared light, ultraviolet light, etc.) that falls on it. This also means that it will also radiate at all frequencies that heat energy produces in it.

  3. Black-body radiation - Wikipedia, the free encyclopedia

    en.wikipedia.beta.wmflabs.org/wiki/Black-body...
    • Spectrum
    • Explanation
    • Equations
    • Human Body Emission
    • Temperature Relation Between A Planet and Its Star
    • Cosmology
    • Doppler Effect For A Moving Black Body
    • History
    • Further Reading
    • External Links

    Black-body radiation has a characteristic, continuous frequency spectrum that depends only on the body's temperature,[8] called the Planck spectrum or Planck's law. The spectrum is peaked at a characteristic frequency that shifts to higher frequencies with increasing temperature, and at room temperature most of the emission is in the infrared region of the electromagnetic spectrum.[9][10][11] As the temperature increases past about 500 degrees Celsius, black bodies start to emit significant amounts of visible light. Viewed in the dark, the first faint glow appears as a "ghostly" grey. With rising temperature, the glow becomes visible even when there is some background surrounding light: first as a dull red, then yellow, and eventually a "dazzling bluish-white" as the temperature rises.[12][13] When the body appears white, it is emitting a substantial fraction of its energy as ultraviolet radiation. The Sun, with an effective temperature of approximately 5800 K,[14] is an approximate...

    All normal (baryonic) matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a body's thermal energy into electromagnetic energy, and is therefore called thermal radiation. It is a spontaneous process of radiative distribution of entropy. Conversely all normal matter absorbs electromagnetic radiation to some degree. An object that absorbs all radiation falling on it, at all wavelengths, is called a black body. When a black body is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature. Its emission is called black-body radiation. The concept of the black body is an idealization, as perfect black bodies do not exist in nature.[15] Graphite and lamp black, with emissivities greater than 0.95, however, are good approximations to a black material. Experimentally, black-body radiation may be established best as the ultimately stable steady state equilibrium...

    Planck's law of black-body radiation

    Planck's law states that[30] 1. '"`UNIQ--postMath-00000001-QINU`"' where 1. I(ν,T) is the energy per unit time (or the power) radiated per unit area of emitting surface in the normal direction per unit solid angle per unit frequency by a black body at temperature T, also known as spectral radiance; 2. h is the Planck constant; 3. c is the speed of lightin a vacuum; 4. k is the Boltzmann constant; 5. ν is the frequencyof the electromagnetic radiation; and 6. T is the absolute temperatureof t...

    Wien's displacement law

    Wien's displacement lawshows how the spectrum of black-body radiation at any temperature is related to the spectrum at any other temperature. If we know the shape of the spectrum at one temperature, we can calculate the shape at any other temperature. Spectral intensity can be expressed as a function of wavelength or of frequency. A consequence of Wien's displacement law is that the wavelength at which the intensity per unit wavelengthof the radiation produced by a black body is at a maximum,...

    Stefan–Boltzmann law

    The Stefan–Boltzmann lawstates that the power emitted per unit area of the surface of a black body is directly proportional to the fourth power of its absolute temperature: 1. '"`UNIQ--postMath-00000005-QINU`"' where j*is the total power radiated per unit area, T is the absolute temperature and σ = 5.67×10−8 W m−2 K−4 is the Stefan–Boltzmann constant. This follows from integrating '"`UNIQ--postMath-00000006-QINU`"' over frequency and solid angle: 1. '"`UNIQ--postMath-00000007-QINU`"' Th...

    As all matter, the human body radiates some of a person's energy away as infraredlight. The net power radiated is the difference between the power emitted and the power absorbed: 1. '"`UNIQ--postMath-00000014-QINU`"' Applying the Stefan–Boltzmann law, 1. '"`UNIQ--postMath-00000015-QINU`"' The total surface area of an adult is about 2 m2, and the mid- and far-infrared emissivity of skin and most clothing is near unity, as it is for most nonmetallic surfaces.[33][34] Skin temperature is about 33 °C,[35] but clothing reduces the surface temperature to about 28 °C when the ambient temperature is 20 °C.[36]Hence, the net radiative heat loss is about 1. '"`UNIQ--postMath-00000016-QINU`"' The total energy radiated in one day is about 9 MJ (megajoules), or 2000 kcal (food calories). Basal metabolic rate for a 40-year-old male is about 35 kcal/(m2·h),[37] which is equivalent to 1700 kcal per day assuming the same 2 m2 area. However, the mean metabolic rate of sedentary adults is about...

    The black-body law may be used to estimate the temperature of a planet orbiting the Sun. The temperature of a planet depends on several factors: 1. Incident radiation from its star 2. Emitted radiation of the planet, e.g., Earth's infrared glow 3. The albedoeffect causing a fraction of light to be reflected by the planet 4. The greenhouse effectfor planets with an atmosphere 5. Energy generated internally by a planet itself due to radioactive decay, tidal heating, and adiabatic contraction due by cooling. The analysis only considers the Sun's heat for a planet in a Solar System. The Stefan–Boltzmann law gives the total power(energy/second) the Sun is emitting: 1. '"`UNIQ--postMath-00000018-QINU`"' where 1. '"`UNIQ--postMath-00000019-QINU`"' is the Stefan–Boltzmann constant, 2. '"`UNIQ--postMath-0000001A-QINU`"' is the effective temperature of the Sun, and 3. '"`UNIQ--postMath-0000001B-QINU`"' is the radius of the Sun. The Sun emits that power equally in all directions. Becau...

    The cosmic microwave background radiation observed today is the most perfect black-body radiation ever observed in nature, with a temperature of about 2.7 K.[51] It is a "snapshot" of the radiation at the time of decouplingbetween matter and radiation in the early universe. Prior to this time, most matter in the universe was in the form of an ionized plasma in thermal, though not full thermodynamic, equilibrium with radiation. According to Kondepudi and Prigogine, at very high temperatures (above 1010 K; such temperatures existed in the very early universe), where the thermal motion separates protons and neutrons in spite of the strong nuclear forces, electron-positron pairs appear and disappear spontanteously and are in thermal equilibrium with electromagnetic radiation. These particles form a part of the black body spectrum, in addition to the electromagnetic radiation.[52]

    The relativistic Doppler effect causes a shift in the frequency f of light originating from a source that is moving in relation to the observer, so that the wave is observed to have frequency f': 1. '"`UNIQ--postMath-00000033-QINU`"' where v is the velocity of the source in the observer's rest frame, θ is the angle between the velocity vector and the observer-source direction measured in the reference frame of the source, and c is the speed of light.[53] This can be simplified for the special cases of objects moving directly towards (θ = π) or away (θ = 0) from the observer, and for speeds much less than c. Through Planck's law the temperature spectrum of a black body is proportionally related to the frequency of light and one may substitute the temperature (T) for the frequency in this equation. For the case of a source moving directly towards or away from the observer, this reduces to 1. '"`UNIQ--postMath-00000034-QINU`"' Here v > 0 indicates a receding source, and v< 0 indica...

    Balfour Stewart

    In 1858, Balfour Stewart described his experiments on the thermal radiative emissive and absorptive powers of polished plates of various substances, compared with the powers of lamp-black surfaces, at the same temperature.[23] Stewart chose lamp-black surfaces as his reference because of various previous experimental findings, especially those of Pierre Prevost and of John Leslie. He wrote "Lamp-black, which absorbs all the rays that fall upon it, and therefore possesses the greatest possible...

    Gustav Kirchhoff

    In 1859, not knowing of Stewart's work, Gustav Robert Kirchhoff reported the coincidence of the wavelengths of spectrally resolved lines of absorption and of emission of visible light. Importantly for thermal physics, he also observed that bright lines or dark lines were apparent depending on the temperature difference between emitter and absorber.[55] Kirchhoff then went on to consider bodies that emit and absorb heat radiation, in an opaque enclosure or cavity, in equilibrium at temperature...

    Kroemer, Herbert; Kittel, Charles (1980). Thermal Physics (2nd ed.). W. H. Freeman Company. ISBN 0-7167-1088-9.
    Tipler, Paul; Llewellyn, Ralph (2002). Modern Physics (4th ed.). W. H. Freeman. ISBN 0-7167-4345-0.
  4. Cosmic microwave background - Wikipedia

    en.wikipedia.org/wiki/Cosmic_microwave...

    The cosmic microwave background radiation is an emission of uniform, black body thermal energy coming from all parts of the sky. The radiation is isotropic to roughly one part in 100,000: the root mean square variations are only 18 µK, [8] after subtracting out a dipole anisotropy from the Doppler shift of the background radiation.

  5. People also ask

    What is blackbody radiation?

    Does blackbody absorb radiation?

    What type of radiation does black body emit?

    Did classical physics work for blackbody radiation?

  6. Stefan–Boltzmann law - Wikipedia

    en.wikipedia.org/wiki/Stefan–Boltzmann_law

    So long as the geometry of the surface does not cause the blackbody to reabsorb its own radiation, the total energy radiated is just the sum of the energies radiated by each surface; and the total surface area is just the sum of the areas of each surface—so this law holds for all convex blackbodies, too, so long as the surface has the same temperature throughout.

  7. Thermometer - Wikipedia

    en.wikipedia.org/wiki/Thermometer

    Blackbody radiation All objects above absolute zero emit blackbody radiation for which the spectra is directly proportional to the temperature. This property is the basis for a pyrometer or infrared thermometer and thermography. It has the advantage of remote temperature sensing; it does not require contact or even close proximity unlike most ...

  8. Rayleigh–Jeans law - Wikipedia

    en.wikipedia.org/wiki/Rayleigh–Jeans_law

    The same argument can be applied to the blackbody radiation expressed in terms of frequency ν = c/λ. In the limit of small frequencies, that is h ν ≪ k B T {\displaystyle h u \ll k_{\mathrm {B} }T} ,

  9. People also search for