A) \[{{21}^{o}}C\]
B) \[{{22}^{o}}C\]
C) \[{{24}^{o}}C\]
D) \[{{28}^{o}}C\]
Correct Answer: D
Solution :
The total energy radiated from a black body per minute. \[Q\propto {{T}^{4}}\] Þ \[\frac{{{Q}_{2}}}{{{Q}_{1}}}={{\left( \frac{2T}{T} \right)}^{4}}=16\] Þ \[{{Q}_{2}}=16{{Q}_{1}}\] If m be mass of water taken and S be its specific heat capacity, then \[{{Q}_{1}}=ms(20.5-20)\] and \[{{Q}_{2}}=ms(\theta -20)\] \[\theta {}^\circ C=\]Final temperature of water Þ \[\frac{{{Q}_{2}}}{{{Q}_{1}}}=\frac{\theta -20}{0.5}\] Þ \[\frac{16}{1}=\frac{\theta -20}{0.5}\] Þ \[\theta =28{}^\circ C\]
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