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 radiys r, whose outer surface radiates as a black body at a temperature T K is given by

Options

A. `sigmar^(4)T^(4)//r^(4)`
B. `4pisigmar^(2)T^(4)//R^(2)`
C. `sigmar^(2)T^(4)//R^(2)`
D. `sigmar^(2)T^(4)//4pir^(2)`

Answer

C

Explanation

`(dE)/(A)=(sigma4pir^(2)T^(4))/(4piR^(2))=(sigmar^(2)T^(4))/(R^(2))`

Correct choice is (c ).