BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    The pressure and density of a diatomic gas \[\left( \gamma =\frac{7}{5} \right)\]change adiabatically from (P, d) to (P, d). If \[\frac{d}{d}=32,\] then\[\frac{P}{P}\] should be:

    A) \[\frac{1}{128}\]           

    B)                                        32

    C)         128                                       

    D)         None of these

    Correct Answer: C

    Solution :

    In an adiabatic process \[P{{V}^{\gamma }}=\text{constant}\]                 Now,     \[\text{volume = }\frac{\text{mass}}{\text{density}}\]                 i.e.,        \[V=\frac{M}{d}\]                 \[\therefore \]  \[P{{\left[ \frac{M}{d} \right]}^{\gamma }}=\text{constant}\]                 or            \[\frac{P}{{{d}^{\gamma }}}=a,\]new constant.                 or            \[\frac{P}{{{d}^{\gamma }}}=\frac{P}{{{d}^{\gamma }}}\]                 or            \[\frac{P}{P}={{\left( \frac{d}{d} \right)}^{\gamma }}\]                 but         \[\frac{d}{d}=32\]and \[\gamma =\frac{7}{5}\]                 \[\therefore \]  \[\frac{P}{P}={{(32)}^{7/5}}={{\left[ {{(32)}^{1/5}} \right]}^{7}}\]                                 \[={{2}^{7}}\]                                 \[=128\]


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