Question

Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t°C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is

(a) r²σ(t+273)⁴/4πR² 

(b) 16π²r²σt⁴/R²

(c)  r²σ(t+273)⁴/R²

(d) 4πr²σt²/R²

Answer 1

Correct option (c)  r²σ(t+273)⁴/R²

Explanation:

Power P radiated by the sun with its surface temperature (t + 273) K is given by Stefan's Boltzmann law.

where r is the radius of the sun and the sun is treated as a black body where e = 1. The radiant power per unit area received by the surface at a distance R from the centre of the sun is given by