A black body at a temperature of ${227^o}C$ radiates heat energy at the rate of $5 cal/cm^2-sec$. At a temperature of ${727^o}C$, the rate of heat radiated per unit area in $cal/cm^2$ will be
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(a) $\frac{{{E_2}}}{{{E_1}}} = {\left( {\frac{{{T_2}}}{{{T_1}}}} \right)^4}$$ = \left( {\frac{{273 + 727}}{{237 + 227}}} \right) = \frac{{{{(1000)}^4}}}{{{{(500)}^4}}} = 16 \Rightarrow {E_2} = 80$
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