Given: The surface temperature of the sun is
T0 and it is at average distance d from a planet. The radius of the sun is R.
To find the temperature at which planet radiates the energy.
Solution:
Let P be power radiated by the sun
Given, R is radius of the sun, d is average distance between sun and planet and T0 is the surface temperature of the sun
if T is the temperature at which planet radiates the energy.
Energy received by the planet = WA=σT4(4πd2)
where W=σT4 is the flux and A is the area
Energy radiated by planet = (4πR2)σT40
For thermal equilibrium,
σT4(4πd2)=(4πR2)σT40⟹T4=R2T40d2⟹T=(R2T40d2)14
is the temperature at which planet radiates the energy.