CMC Medical CMC-Medical VELLORE Solved Paper-2015

  • question_answer
    One mole of a perfect gas expends adiabatically. As a result of this, its temperature, pressure and volume changes \[{{T}_{1}},{{p}_{1}},{{V}_{1}}\] to \[{{T}_{2}},{{p}_{2}}\] and \[{{V}_{2}}\] respectively. If molar specific heat of constant volume is \[{{C}_{V}},\] then the work done by the gas is

    A)  \[2.303{{p}_{1}}{{V}_{1}}\log \left( \frac{{{V}_{2}}}{{{V}_{1}}} \right)\]

    B)  \[R{{T}_{1}}\log \left( \frac{{{V}_{2}}}{{{V}_{1}}} \right)\]

    C)  \[\frac{p_{1}^{2}\,V_{1}^{2}-p_{2}^{2}\,V_{2}^{2}}{R({{T}_{2}}-{{T}_{1}})}\]

    D)  \[{{C}_{V}}({{T}_{1}}-{{T}_{2}})\]

    E)  \[R\,{{C}_{V}}\left( \frac{{{T}_{1}}+{{T}_{2}}}{2} \right)\]

    Correct Answer: D

    Solution :

                    Work done during adiabatic expansion \[W=\frac{R\,({{T}_{1}}-{{T}_{2}})}{(\gamma -1)}\] Since, \[\gamma =\frac{{{C}_{p}}}{{{C}_{V}}}\] and \[{{C}_{p}}-{{C}_{V}}=R\] \[\therefore \]  \[W=\frac{({{C}_{p}}-{{C}_{V}})\,({{T}_{1}}-{{T}_{2}})}{({{C}_{p}}-{{C}_{V}})/{{C}_{V}}}\] \[\Rightarrow \]               \[W={{C}_{V}}({{T}_{1}}-{{T}_{2}})\]


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