NEET Sample Paper NEET Sample Test Paper-19

  • question_answer
    When the temperature of a black body increases, it is observed that the wavelength corresponding to maximum energy changes from \[0.26\,\mu m\]to \[0.13\,\mu m.\] The ratio of the emissive powers of the body at the  respective temperatures is:

    A) \[\frac{16}{1}\]                                  

    B) \[\frac{4}{1}\]

    C) \[\frac{1}{4}\]                        

    D) \[\frac{1}{16}\]   

    Correct Answer: D

    Solution :

    By wein's displacement law      \[{{\lambda }_{1}}{{T}_{1}}={{\lambda }_{2}}{{T}_{2}}\] or \[\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{{{T}_{2}}}{{{T}_{1}}}=\frac{0.26}{0.13}=2\] \[\therefore \]\[{{T}_{2}}=2{{T}_{1}}\] By stefan's Law, emissive power \[E=\sigma {{T}^{4}}\] \[\therefore \]\[{{E}_{1}}=\sigma T_{1}^{4},{{E}_{2}}=\sigma T_{2}^{4},\] \[\therefore \]\[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{\sigma T_{1}^{4}}{\sigma {{(2{{T}_{1}})}^{4}}}=\frac{1}{16}\] Hence, the correction option is [d].


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