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Homework Help: Stefan Law

  1. May 4, 2009 #1
    The Earth has a surface temperature around 270 K and an emissivity of 0.8, while space has a temperature of around 2 K.
    Use Stefan's law: P(net) = 5.67×10-8 W/K4 m2 *A*e*(T4 - To4) to solve the following questions.
    (Radii of the Earth and the Sun are Re = 6.38×106 m, Rs = 7×108 m.)

    (a) What is the net power radiated from our Earth into free space in Watt W?

    I came up with an answer of 1.54*10^17...is that what you came up with? (just use the equation mentioned above and A=4*Pi*Re2, e=.8, T= 270, To=2)
  2. jcsd
  3. May 4, 2009 #2


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    Looks like the right values to input. Estimating it with orders of magnitude looks about right.
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