Manipal Medical Manipal Medical Solved Paper-2010

  • question_answer
    At\[273{}^\circ C,\]the emissive power of a perfect black body is R. What is its value at\[0{}^\circ C,\]?

    A)  \[\frac{R}{4}\]

    B)  \[\frac{R}{16}\]

    C)  \[\frac{R}{2}\]

    D)  None of the above

    Correct Answer: B

    Solution :

     From Stefans law, the total radiant energy emitted per second per unit surface area of a black body is proportional t6 the fourth power of the absolute temperature (T) of the body. \[\therefore \] \[E=\sigma {{T}^{4}}\] where,\[\sigma \]is Stefans constant. Given,  \[{{E}_{1}}=R,{{T}_{1}}=273{}^\circ C\] \[=273+273=546\text{ }K\] \[{{T}_{2}}=0{}^\circ C=273K\] \[\therefore \] \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{T_{1}^{4}}{T_{2}^{4}}\] \[\Rightarrow \] \[{{E}_{2}}=\frac{T_{2}^{4}}{T_{1}^{4}}{{E}_{1}}\] \[\Rightarrow \] \[{{E}_{2}}=\frac{{{(273)}^{4}}}{{{(546)}^{4}}}R\] \[\therefore \] \[{{E}_{2}}=\frac{R}{16}\]


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