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Net Power vs. Net Radiated

  1. Apr 7, 2005 #1
    Two identical objects are placed in a room at 26°C. Object 1 has a temperature of 81°C and object 2 has a temperature of 35°C. What is the ratio of the net power emitted by object 1 to that radiated by object 2?

    Answer is supposed to be (power emitted by 1 / power emitted by 2)

    I've tried a couple of different ways but it's always reported them wrong:

    [itex]P = e*\sigma*AT^4[/itex]

    So I did: (81^4) / (35^4-26^4)
    I also tried: (81^4-26^4)/(35^4-26^4)

    Both wrong. I've tried all the following answers:
    41
    40.8
    77.6

    Help would be appreciated.
     
  2. jcsd
  3. Apr 8, 2005 #2

    xanthym

    User Avatar
    Science Advisor

    You need to use Temperatures in Degrees KELVIN. Try recalculating the ratio of net 4th powers of Temp (degKELVIN) given by:
    {Ratio of NET Power Radiated} = {(T1)4 - (Ta)4}/{(T2)4 - (Ta)4} ::: <---- Use DegKELVIN


    ~~
     
    Last edited: Apr 8, 2005
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