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. `rho r^(2) T^(4)//R^(2)`
B. `rho R^(2)T^(4)//4pi R^(2)`
C. `rho r^(2)T^(4)//4pi r^(2)`
D. `4pi rho r^(2)T&^(4)//R^(2)`

Answer

A

Explanation

Total rediant energy per unit area
`=(rho(4pir^(2))T^(4))/(4piR^(2))=(rho^(2)T^(4))/(R^(2))`