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 `T K` is given by
(where `sigma` is Stefan's constant)

Options

A. `sigma r^4 T^4 // r^4`
B. `4pi sigma r^2 T^4 // R^2`
C. `sigma r^2 T^4 // R^2`
D. `sigma r^2 T^4 // 4pi r^2`

Answer

C

Explanation

Total radiant energy received per unit area

`(P)/(4pi R^2) = (sigma 4pi r^2 T^4)/(4pi R^2) `
` = (sigma r^2 T^4)/(R^2)`