A black body radiates $ 20\,W$ at temperature ${227^o}C$. If temperature of the black body is changed to ${727^o}C$ then its radiating power will be ..... $W$
AIIMS 2003, Medium
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(c) For a black body $\frac{Q}{t} = P = A\sigma {T^4}$
==> $\frac{{{P_2}}}{{{P_1}}} = {\left( {\frac{{{T_2}}}{{{T_1}}}} \right)^4}$ ==> $\frac{{{P_2}}}{{20}} = {\left( {\frac{{273 + 727}}{{273 + 227}}} \right)^4}$
==> $\frac{{{P_2}}}{{20}} = {(2)^4}$ ==> ${P_2} = 320\,W$
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