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 ....... $kcal/m ^2 \,min$
AIPMT 1998, Medium
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(c) $\frac{{{E_2}}}{{{E_1}}} = {\left( {\frac{{{T_2}}}{{{T_1}}}} \right)^4}$
==>$\frac{{{E_2}}}{{20}} = {\left( {\frac{{2T}}{T}} \right)^4}$ $=16$
==> ${E_2} = 320\;kcal/{m^2}min$ .
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