Assuming the Sun to be a spherical body of radius R at a temperature of T K, evaluate the total radiant power, incident on earth, at a distance r from the Sun : <br> where $r_0$ is the radius of the earth and $\sigma$ is Stefan's constant .

Question

( A ) $R^2 \sigma T^4/r^2$
( B ) $4\pi r^2_0 R^2 \sigma T^4/r^2$
( C ) $\pi r^2_0 R^2 \sigma T^4/r^2$
( D ) $r_0^2 R^2 \sigma T^4/4 \pi r^2$