Manipal Engineering Manipal Engineering Solved Paper-2008

  • question_answer
    Two spheres P and Q, of same colour having radii 8 cm and 2 cm are maintained at temperatures \[127{}^\circ C\] and \[527{}^\circ C\] respectively. The energy radiated by P and Q is

    A)  0.054                                   

    B)  0.0034

    C)  1                            

    D)         2

    Correct Answer: C

    Solution :

    Total energy radiated from a body                    \[Q=A\varepsilon \sigma {{T}^{4}}t\] \[\Rightarrow \]               \[Q\propto A{{T}^{4}}\propto {{r}^{2}}{{T}^{4}}\] \[(\because A=4\pi {{r}^{2}})\] \[\Rightarrow \]               \[\frac{{{Q}_{P}}}{{{Q}_{Q}}}={{\left( \frac{{{r}_{P}}}{{{r}_{Q}}} \right)}^{2}}{{\left( \frac{{{T}_{P}}}{{{T}_{Q}}} \right)}^{4}}\]                        \[={{\left( \frac{8}{2} \right)}^{2}}{{\left[ \frac{273+127}{273+527} \right]}^{4}}=1\]


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