The radiant energy from the Sun incident normally at the surface of earth is `20kcal//m^(2)` min What would have been the radiant energy incident normally on the earth if the sun had a temperature twice of the present one ? .

Options

A. `160 kcal//m^(2)` min
B. `40 kcal//m^(2)` min
C. `320 kcal//m^(2)` min
D. `80 kcal//m^(2)` min

Answer

C

Explanation

(3) Intensity reaching earth
`I = (u)/(4 pi r^(2)) = (e sigma AT^(4))/(4 pi r^(2))`
`(I')/(I) = ((2T)/(T))^(4) =16`
`I' = 16 I = 16 xx 20 = 320 kcal//m^(2)` min