JEE Main & Advanced JEE Main Paper (Held on 12-4-2019 Afternoon)

  • question_answer
                The number density of molecules of a gas depends on their distance r from the origin as, \[n(r)={{n}_{0}}{{e}^{-\alpha {{r}^{4}}}}.\]Then the total number of molecules is proportional to : [JEE Main 12-4-2019 Afternoon]

    A) \[{{n}_{0}}{{\alpha }^{1/4}}\]                 

    B) \[{{n}_{0}}{{\alpha }^{-3}}\]

    C) \[{{n}_{0}}{{\alpha }^{-3/4}}\]    

    D)   \[\sqrt{{{n}_{0}}}{{\alpha }^{1/2}}\]

    Correct Answer: C

    Solution :

    Given number density of molecules of gas as a function of r is\[n(r){{n}_{0}}{{e}^{-\alpha {{r}^{4}}}}\] \[\therefore \]Total number of molecule\[=\int\limits_{0}^{\infty }{n(r)}dV\] \[=\int\limits_{0}^{\infty }{{{n}_{0}}{{e}^{-\alpha {{r}^{4}}}}4\pi {{r}^{2}}}dr\] \[\therefore \]Number of molecules is proportional to\[{{n}_{0}}{{\alpha }^{-3/4}}\]


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