JEE Main & Advanced Sample Paper JEE Main - Mock Test - 44

  • question_answer
    A vessel is partitioned in two equal halves by a fixed diathermic separator. Two different ideal gases are filled in left (L) and right (R) halves. The rms speed of the molecules in L part is equal to the mean speed of molecules in the R part. Then the ratio of the mass of a molecule in L part to that of a molecule in R part is -

    A) \[\sqrt{\frac{3}{2}}\]           

    B)                    \[\sqrt{\pi /4}\]

    C) \[\sqrt{2/3}\]           

    D)        \[3\pi /8\]

    Correct Answer: D

    Solution :

    [d] Root means square velocity of molecule in left part \[{{V}_{rms}}=\sqrt{\frac{3KT}{{{m}_{L}}}}\] Mean or average speed of molecule in right part \[{{V}_{av}}=\sqrt{\frac{8\,KT}{\pi \,{{m}_{R}}}}\] According to problem \[\sqrt{\frac{3KT}{{{m}_{L}}}}=\sqrt{\frac{8\,KT}{\pi \,{{m}_{R}}}}\] \[\Rightarrow \frac{3}{{{m}_{L}}}=\frac{8}{\pi {{m}_{R}}}\] \[\Rightarrow \frac{{{m}_{L}}}{{{m}_{R}}}=\frac{3\pi }{8}\]


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