AIIMS AIIMS Solved Paper-2004

  • question_answer
    \[{{V}_{rms}},{{V}_{av}}\] and \[{{V}_{rms}}\] are root mean square, average and most probable speeds of molecules of a gas obeying Maxwellian velocity distribution. Which of the following statements is correct?

    A) \[{{V}_{rms}}<{{V}_{av}}<{{V}_{mp}}\]

    B) \[{{V}_{rms}}>{{V}_{av}}>{{V}_{mp}}\]

    C)       \[{{V}_{mp}}<{{V}_{rms}}<{{V}_{av}}\]

    D)        \[{{V}_{mp}}>{{V}_{rms}}>{{V}_{av}}\]

    Correct Answer: B

    Solution :

    Root mean square speed. The root mean square speed is used to measure the velocity of particles in a gas. It is given by \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}}=1.732\sqrt{\frac{RT}{M}}\]                   ?...(1) where M is molar mass and R is gas constant, T is temperature. Most probable speed \[{{v}_{p}}\], is the speed most likely to be possessed by any molecule in the system. \[{{v}_{av}}=\sqrt{\frac{2RT}{M}}=1.41\sqrt{\frac{RT}{M}}\]                                       ??(2) whereas mean speed is \[{{v}_{mp}}=\sqrt{\frac{8RT}{\pi M}}=1.6\sqrt{\frac{RT}{M}}\]                 .?..(3) From Eqs. (1), (2) and (3), we conclude that \[{{v}_{rms}}>{{v}_{av}}>{{v}_{mp}}\]


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