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Homework Help: Radiation problem

  1. May 1, 2008 #1
    Hey guys having some trouble with this question its a new topic in my course

    The Earth receives solar radiation at a rate of 342 W/m2 averaged over the total surface of the Earth. About
    30% of this radiation gets reflected back into space while the rest is absorbed. For the Earth to maintain thermal
    equilibrium (not to heat up), the absorbed energy must be transferred back into space.
    a) With reference to the heat transfer mechanisms briefly describe how this transfer must occur
    (1-2 sentences).
    b) How much power per square meter must be transferred back into space to maintain thermal equilibrium?
    c) If we treat the Earth as a black body ob ject (with emissivity e = 0.602) radiating out into space, calculate what
    the average temperature the surface of the earth must be in order to lose this amount of heat.
  2. jcsd
  3. May 1, 2008 #2
    The first one should be simple, as there are only 3 mechanisms of heat transfer, and 2 of them require physical contact between bodies.

    What work have you done to solve the other two parts?
  4. May 1, 2008 #3

    This is more then likely wrong but for part B i said 70% of power had to be transferred back to maintain equilibrium so therefore 239.4 W/m^2

    And for Part C I used T^4 = P/(e*"boltz constant"*Area)

    Which then became

    T = 4Sqrt(239.4 W/m^2/(0.602*5.67*10^-8*4*pi*6378000m^2)
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