JCECE Engineering JCECE Engineering Solved Paper-2006

  • question_answer
    For monoatomic gas which is correct?

    A) \[CV=\frac{3}{5}R\]                        

    B) \[{{C}_{P}}=\frac{5}{2}R\]

    C)  \[{{C}_{P}}-{{C}_{V}}=2R\]         

    D)  \[\frac{{{C}_{P}}}{{{C}_{V}}}=\frac{3}{5}\]

    Correct Answer: B

    Solution :

    Key Idea: Monoatomic gas has three translational degrees of freedom. Specific heat at constant volume\[({{C}_{V}})=\frac{f}{2}R\] and specific heat at constant pressure\[({{C}_{P}})\]                 \[{{C}_{P}}=\left( \frac{f}{2}+1 \right)R\] For monoatomic gas\[f=3\] \[\therefore \]  \[{{C}_{V}}=\frac{3}{2}R,\,\,{{C}_{P}}=\left( \frac{3}{2}+1 \right)R=\frac{5}{2}R\] From Mayor's formula                 \[{{C}_{P}}-{{C}_{V}}=R\] \[\therefore \]  \[\frac{5}{2}R-\frac{3}{2}R=R\] and        \[\gamma =\frac{{{C}_{P}}}{{{C}_{V}}}=\frac{5/2}{3/2}=\frac{5}{3}\]


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