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Homework Help: Validate the Stefan Boltzmann equation

  1. Nov 30, 2017 #1
    1. The problem statement, all variables and given/known data
    You are performing an experiment to validate the Stefan Boltzmann equation. What irradiance would you measure at a temperature of 109C? The emissivity of your thermal heat source is 0.81 and your thermopile measures 0 W/m2 at 27 C when directed towards a blackbody. Submit your answer in units of W/m2, do not include the units in your answer.

    Answer tolerance is +/- 0.2%.

    2. Relevant equations
    E=σeT^4

    3. The attempt at a solution

    I presume I have to work out a correction factor like this:
    Ec=081*5.67E-8*300^4=372 W/m2
    Then calculate measured irradiance:
    E=5.67E-8*382^4*1=1207
    Then I have to add the correction factor Ec to E to get the measured irradiance (Em):
    Em=Ec+E=1579 w/m2

    Am I doing it right?

    Thanks for your answers.
     
  2. jcsd
  3. Dec 1, 2017 #2
    Hello,

    1. Why do you assume the emissivity to be 1 when the temperature is 382 K?
    2. Why do you add (and not subtract) the correction factor? Just think that your zero is at 372 W/m2.
     
  4. Dec 1, 2017 #3
    1. Ohh, I get it know. I used 1 because of the blackbody, but I know now that is irrelevant. :)
    2.I added the correction factor because the thermopile should measure 0 at 0 Kelvin. Therefore, the measured irradiance is always less by 372 W/m2.
     
  5. Dec 1, 2017 #4
    Exactly, the measured E must be less than the real by 372 W/m2. So, Emeasured=Ereal-Ecorrection.

    Your equation implies that the measured E is bigger than the real E (by 372 W/m2).
     
  6. Dec 1, 2017 #5
    Ohh, yes. I understand it know. Thank you! :-)
     
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