BCECE Medical BCECE Medical Solved Papers-2008

  • 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 \[{{C}_{p}}/{{C}_{V}}\]for the gas is

    A)  4/3            

    B)  2

    C)  5/3            

    D)  3/2

    Correct Answer: D

    Solution :

    Key Idea For adiabatic process\[p{{V}^{\gamma }}=\]constant. 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                 \[{{p}^{1-\gamma }}{{T}^{\gamma }}=\] 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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