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6 c-radiation-stefan boltzman

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It contains a brief description of the Stefan-Boltzmann law, used in the class of Hydrology at the University of Trento

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6 c-radiation-stefan boltzman

  1. 1. Riccardo Rigon IlSole,F.Lelong,2008,ValdiSella Solar Radiation The Stefan-Boltzmann law
  2. 2. R. Rigon Radiation emitted emissivity Stefan-Boltzmann constant absolute temperatureR = ✏ T4 Every body with a temperature different than T=0 K emits radiation as a function of its temperature according to the Stefan-Boltzmann law The Stefan-Boltzmann law 10 2 The Sun
  3. 3. R. Rigon RSun = ✏ T4 = 1 ⇤ 5.67 ⇤ 10 8 ⇤ 60004 ⇡ 25.12 ⇤ 109 J m 2 s 1 The physics of Radiation On the basis of the temperature of the Sun photosphere (~6000 K), and the Stephan-Boltzmann law, the total energy emitted by the Sun is 11 3 The Sun
  4. 4. R. Rigon The Sun is practically a blackbody. The difference between a true blackbody and the Sun is due to the fact that the corona and the chromosphere selectively absorb certain wavelengths. The Sun is nearly a “blackbody”! 12 4 The Sun
  5. 5. R. Rigon The area below the curves is given by the Stefan-Boltzmann law. The curves themselves are given by Planck’s law. The Sun is nearly a “blackbody”! 13 5 The Sun
  6. 6. R. Rigon The complete electromagnetic spectrum The spectrum of solar radiation stretches far beyond the visible band where, however, nearly half the available energy is concentrated Figure2.9 C.B.Agee 16 6 The Sun
  7. 7. R. Rigon Planck’s Law •Planck’s law is the general law for electromagnetic emission from the surface of a blackbody*: W = 2⇡c2 h 5 e ch KT 1 [Wm 2 µm 1 ] 14 7 The Sun * Stefan-Boltzmann law is just the integration of Plank’s law over wavelengths

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