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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: StephanBoltzman 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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This note was uploaded on 12/29/2011 for the course AST 350 taught by Professor Dion during the Fall '09 term at SUNY Stony Brook.
 Fall '09
 dion

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