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METR 415/715

METR 415/715. MondayFeb 18 2013. Planck’s function. Intensity vs. radiative flux. Remember the units used in Intensity (Wm -2 sr -1 ) and in Flux ( Wm -2 ). Intensity refers to radiation travelling in a certain direction , and Flux to radiation emitted in all directions

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METR 415/715

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  1. METR 415/715 MondayFeb 18 2013

  2. Planck’s function

  3. Intensity vs. radiative flux Remember the units used in Intensity (Wm-2sr-1) and in Flux (Wm-2). Intensity refers to radiation travelling in a certain direction, and Flux to radiation emitted in all directions The left hand side of Planck function refers to the intensityof radiation for a particular wavelength

  4. Wien’s Displacement Law • Refers to the wavelength of maximum emission of Planck’s Function • Obtained by taking the derivative with respect to wavelength and setting it = 0 • ΚW= 2897μm K

  5. Wien’s Displacement Law • Refers to the wavelength of maximum emission of Planck’s Function • Obtained by taking the derivative with respect to wavelength and setting it = 0 • ΚW= 2897μm K

  6. Gray Bodies You assume the emissivity (and hence absorptivity) is a constant fraction of black body emissivity across all wavelengths

  7. Stefan – Boltzmann Law • Obtained by integrating Planck’s function over all wavelengths (eq. 6.4) p.122. • σ = 5.67 X 10-8 Wm-2K4

  8. Monochromatic emissivity – Graybodyemissivity

  9. Krichhoff’s Law

  10. Brightness temperature

  11. Discussion of Fig 6.6 p.129

  12. Discussion of Section 6.4 Radiative equilibrium in a vacuum

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