Calculating Total Power Emitted by a Black Body in a Spherical Chamber

[Krushnaraj Pandya]

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

 

[kuruman]

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?

 

[Krushnaraj Pandya]

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?

 

[kuruman]

Yes.

 

[Krushnaraj Pandya]

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?

 

[Krushnaraj Pandya]

?

 

[haruspex]

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.

 

[Krushnaraj Pandya]

Yes.

Thank you very much :D