How Does a Sphere Exchange Thermal Radiation in Different Temperatures?

[bmb2009]

Homework Statement

A sphere of radius .5m, temperature of 27 deg C, and emissivity = .85 is located in an environment of temperature 77 deg C. At what rate does the sphere (a)emit and (b)absorb thermal radiation? (c)What's the sphere's net rate of energy exchange?

Homework Equations

The Attempt at a Solution

(a). I know I must use the equation P = d(ε)(A)(T^4) where d = stefan-Boltz constant, ε= emissivity, A=surface area, T=temperature...but which temperature is it? I believe I should use the Sphere's temp for the emission quantity and the temp of the enviorment for the absorption radiation quantity. Is that correct?

(c) I haven't been given an equation for net rate of energy exchange but wouldn't it just be absorption - emission ?

Thanks for the help!

 

[haruspex]

Yes, that all looks right to me. Degrees K, of course.

 

[rude man]

Homework Statement

a sphere of radius .5m, temperature of 27 deg c, and emissivity = .85 is located in an environment of temperature 77 deg c. At what rate does the sphere (a)emit and (b)absorb thermal radiation? (c)what's the sphere's net rate of energy exchange?

Homework Equations

The Attempt at a Solution

(a). I know i must use the equation p = d(ε)(a)(t^4) where d = stefan-boltz constant, ε= emissivity, a=surface area, t=temperature...but which temperature is it? I believe i should use the sphere's temp for the emission quantity and the temp of the enviorment for the absorption radiation quantity. Is that correct?

(c) i haven't been given an equation for net rate of energy exchange but wouldn't it just be absorption - emission ?

Thanks for the help!

a-ok.