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Homework Help: Black body

  1. Dec 11, 2005 #1
    How many times more energy is emitted from a black body at 550. degrees C than at a room temperature of 22.0 degrees C.
    So I know that a double in temperature increases energy by 2^4=16 so would I just do 25^4=390625 for this problem?
  2. jcsd
  3. Dec 11, 2005 #2


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    Well assuming the radiant heat flux is given by Q is proportional to T4, then Q1/Q2 = (T1/T2)4.
  4. Dec 11, 2005 #3


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    Careful with your units. Whenever you plug a temperature into the blackbody formula (or pretty much any other physics-related formula), you'll want to make sure the temperature is in kelvin. This is an important distinction because the zero-point of the celsius scale is defined to be the freezing point of water (roughly), not absolute zero. Once you convert to these units, you should find a much more reasonable value for the ratio of energy outputs. Do you know how to convert to kelvin?

    By the way, the rate of energy output also depends on the surface area. Does the problem specify that the surface areas of the two objects are the same?
  5. Dec 12, 2005 #4
    Ok that makes more sense!! And the problem reads just as I wrote it.
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