Black body radiation

  • #1
Krushnaraj Pandya
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Homework Statement


A spherical body is enclosed in a spherical chamber which acts like a perfectly black body. The reflectance of the body is 0.4 and transmittance is negligible, the temperature of the body and surrounding temperature is constant at T Kelvin. The total power that comes out of the body per unit area is?


Homework Equations


P=σεAT^4

The Attempt at a Solution


reflectance is 0.4 so emissivity is 0.6, power radiated by body per unit area is 0.6σT^4 but the correct answer is σT^4- where am I wrong? I think the reflected radiation shouldn't be counted as coming "out" from the body
 

Answers and Replies

  • #2
kuruman
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I think the reflected radiation shouldn't be counted as coming "out" from the body
If that's the case, from where did the spherical chamber get the radiation it's emitting?
 
  • #3
Krushnaraj Pandya
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If that's the case, from where did the spherical chamber get the radiation it's emitting?
I am confused between the terms "radiating" and "emitting". Are they considered the same?
 
  • #5
Krushnaraj Pandya
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So this is what's going on- the chamber emits σT^4 (per unit area), the body emits 0.6 of it back and reflects 0.4 of it back, correct?
 
  • #7
haruspex
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So this is what's going on- the chamber emits σT^4 (per unit area), the body emits 0.6 of it back and reflects 0.4 of it back, correct?
Yes.
 
  • #8
Krushnaraj Pandya
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