AFMC AFMC Solved Paper-2010

  • question_answer
    Two black metallic spheres of radius 4 m, at 2000 K and 1 m, at 4000 K will have ratio of energy radiation as

    A) 1 : 1                                       

    B) 4 : 1          

    C)  1 : 4                                      

    D) 2 : 1

    Correct Answer: A

    Solution :

    According to Stefan's law\[P=A\,\varepsilon \,\sigma \,{{T}^{4}}\] \[\therefore \]   \[\frac{{{P}_{1}}}{{{P}_{2}}}=\frac{{{A}_{1}}}{{{A}_{2}}}.\frac{T_{1}^{4}}{T_{2}^{4}}\] \[={{\left( \frac{{{R}_{1}}}{{{R}_{2}}} \right)}^{2}}.{{\left( \frac{{{T}_{1}}}{{{T}_{2}}} \right)}^{4}}\]     \[[\because \,A=\pi {{R}^{2}}]\] \[={{\left( \frac{4}{1} \right)}^{2}}\times {{\left( \frac{2000}{4000} \right)}^{4}}=\frac{1}{1}\]


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