Question 36 of 215

The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r,whose outer surface radiates as a black body at a temperature TK is given by 

(a) σr2T4/R2                                       (b) σr2T4/4πr2

(c) σr4T4/r4                                        (d) 4π σr2T4/R2

(where σ is Stefan's constant)