The radiant energy from the sun incident normally at the surface of earth is $20\, \frac{{k\;cal}}{{{m^2}\;min}}$. What would have been the radiant energy incident normally on the earth, if the sun had a temperature twice of the present one ....... $kcal/m ^2 \,min$
A$160$
B$40$
C$320$
D$80$
AIPMT 1998, Medium
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C$320$
c (c) $\frac{{{E_2}}}{{{E_1}}} = {\left( {\frac{{{T_2}}}{{{T_1}}}} \right)^4}$
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