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ay45c3-page25

# ay45c3-page25 - 1.0 Relative Visibility 0.9 0.8 0.7 0.6...

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Unformatted text preview: 1.0 Relative Visibility 0.9 0.8 0.7 0.6 rods "Scotopic" dim light cones "Photopic" bright light 0.5 0.4 red looks "black" in dim light 0.3 0.2 0.1 0.0 350 400 450 500 550 λ (nm) 600 violet blue green yellow orange 650 700 750 red 3.5.4 Integral of the Planck spectrum: Stephan-Boltzman law What is the total energy density in an isotropic radiation eld at constant temperature (e.g. inside a furnace, or a star)? From 3.3.4 we calculate u = 1 I d d = 4c I d c 4 2h 3=c2 d = c eh=kT 1 T 4 1 x3 dx = 4c 2h kh c2 0 ex 1 ZZ Z Z ! Z where x  h=kT . The integral is just a number . You can do it numerically, or look it up in a table of integrals. (Some day you should learn how to do it by contour integration.) The answer is 4=15, so 5 4 u = 815 hkc3 T 4  aT 4 3 49 ...
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