Validate the Stefan Boltzmann equation

[tomadevil]

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.

 

[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.

 

[tomadevil]

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.

 

[DoItForYourself]

Exactly, the measured E must be less than the real by 372 W/m². So, E_measured=E_real-E_correction.

Your equation implies that the measured E is bigger than the real E (by 372 W/m²).

 

[tomadevil]

Ohh, yes. I understand it know. Thank you! :-)