A black body radiates at the rate of $W$ watts at a temperature $T$ . If the temperature of the body is reduced to $T/3$ , it will radiate at the rate of (in Watts)
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(a) $P = \left( {\frac{Q}{t}} \right) \propto {T^4}$
==> $\frac{W}{{{P_2}}} = {\left( {\frac{T}{{T/3}}} \right)^4}$
==> ${P_2} = \frac{W}{{81}}$.
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