The radient energy from the sum incident normally at the surface of earth is 20 k cal/`m^(2)` min. What would have been the radiant energy incident normally on the earth, if the sum had a temperature twice of the present one.

Options

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

Answer

B

Explanation

According to Stefan's law `E prop T^(4)`
`implies (E_(1))/(E_(2))=((T_(1))/(T_(2)))^(4)`
`:. (20)/(E_(2))=((T)/(2T))^(4)=(1)/(16)`
`implies E_(2)=320`kcal/`m^(2)` min