Assuming the sun to be a spherical body of radius R at a temperature ‘T’ K, evaluate the total radiant power incident on earth, at a distance r from the sun. (Take r0 is radius of earth ‘σ’ Stefan’s constant)

Energy radiated per sec by the Sun in all possible directions (Assume the Sun as perfect black body)E=4πR2σT4Intensity (I) of the Sun on the Earth surfaceI=σ4πR2T44πr2=σRr2T4Total radiant energy per sec as received on earth=πr02I=πσRr2r02T4[∴The area of the Earth which receives the energy is only 14 th of total surface area of the Earth (r >> R) whose disc has surface area equal to πr02 w.r.t sun]