BHU PMT BHU PMT (Screening) Solved Paper-2008

  • question_answer
    A mixture of hi moles of monoatomic gas and moles of diatomic gas has\[\frac{{{C}_{p}}}{{{C}_{V}}}=\gamma =1.5\]. Then

    A)  \[{{n}_{1}}={{n}_{2}}\]                 

    B)  \[2{{n}_{1}}={{n}_{2}}\]

    C)  \[{{n}_{1}}=2{{n}_{2}}\]              

    D) \[2{{n}_{1}}=3{{n}_{2}}\]

    Correct Answer: A

    Solution :

                     \[{{f}_{av}}=\frac{total\text{ }number\text{ }of\text{ }degrees\text{ }of\text{ }freedom}{total\text{ }number\text{ }of\text{ }molecules}\] \[=\frac{{{n}_{1}}{{N}_{A}}{{f}_{1}}+{{n}_{2}}{{N}_{A}}{{f}_{2}}}{{{n}_{1}}{{N}_{A}}+{{n}_{2}}{{N}_{A}}}\] \[=\frac{{{n}_{1}}{{f}_{1}}+{{n}_{2}}{{f}_{2}}}{{{n}_{1}}+{{n}_{2}}}\] \[=\frac{3{{n}_{1}}+5{{n}_{2}}}{{{n}_{1}}+{{n}_{2}}}\] Also      \[\gamma =1+\frac{2}{{{f}_{av}}}=1.5\] Or           \[{{f}_{av}}=4\] \[\therefore \]  \[\frac{3{{n}_{1}}+5{{n}_{2}}}{{{n}_{1}}+{{n}_{2}}}=4\] Or           \[{{n}_{1}}={{n}_{2}}\]


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