Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Flux question

  1. Jan 20, 2004 #1
    Ok, here's the question.

    Without the greenhouse gases in earth's atmosphere the temperature would be 250K. With them it is 40K higher (290K). Using the Stefan-Boltzman equation for flux ( F = σT4) what is the percentage of infrared radiation leaving the earth's surface taht is absorbed by the greenhouse gases?


    I spent awhile on this and the best I could come up with is 18%. But if someone else knows how to do this, help will be appreciated. Thanks!
     
  2. jcsd
  3. Jan 21, 2004 #2

    HallsofIvy

    User Avatar
    Science Advisor

    What is the σ? Post that and show how you used it to get 18%.
     
  4. Jan 21, 2004 #3
    σ is the Stefan-Boltzman constant... 5.67 x 10-8 J/m2K4.

    I basically calculated the flux F1 for T = 250K and F2 for T = 290.
    Then I did xF1= F2-F1 and solved for x.
     
  5. Jan 22, 2004 #4

    HallsofIvy

    User Avatar
    Science Advisor

    Okay, now what did you get for F1 and F2? I don't get 18%, I get 81%!
     
  6. Jan 22, 2004 #5
    Hmm, yes I got 81% too. But for some reason it looks like I then did 1-x.

    Is the basic setup even right for approaching this problem?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook