RAJASTHAN PMT Rajasthan - PMT Solved Paper-2007

  • question_answer
    During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature. The ratio\[\frac{{{C}_{p}}}{{{C}_{V}}}\] for the gas is

    A)  \[\frac{4}{3}\]                                  

    B)  \[2\]

    C)  \[\frac{3}{2}\]                  

    D)         \[\frac{3}{2}\]

    Correct Answer: D

    Solution :

    Given that,                 \[p\propto {{T}^{3}}\] or            \[p{{T}^{-3}}=\]constant                               ... (i) Also for adiabatic process,                 \[p{{V}^{\gamma }}=\]constant but         \[pV=RT\]                           (ideal gas law) or            \[V=\frac{RT}{p}\] \[\therefore \]  \[p{{\left( \frac{RT}{p} \right)}^{\gamma }}=\]constant or            \[p{{T}^{\gamma (1-\gamma )}}=\]constant                       ... (ii) Equating Eqs. (i) and (ii), we get                 \[\frac{\gamma }{1-\gamma }=3\] or            \[\gamma =-3+3\gamma \] or            \[2\gamma =3\] \[\therefore \]  \[\gamma =3/2\] or            \[\frac{{{C}_{p}}}{{{C}_{V}}}=3/2\]


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