Validate the Stefan Boltzmann equation

  • Thread starter tomadevil
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  • #1
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Homework Statement


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%.

Homework 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.
 

Answers and Replies

  • #2
DoItForYourself
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.
 
  • #3
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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.
 
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  • #4
DoItForYourself
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).
 
  • #5
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Ohh, yes. I understand it know. Thank you! :-)
 

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