NEET Physics Thermodynamical Processes NEET PYQ-Thermodynamical Processes

  • question_answer
    If the ratio of specific heat of a gas at constant pressure to that at constant volume is \[\gamma ,\] the change in internal energy of a mass of gas when the volume changes from V to 2V at constant pressure P is:                   [AIPMT 1998]

    A)  \[\frac{R}{(\gamma -1)}\]          

    B)       PV                  

    C)  \[\frac{P\,V}{(\gamma -1)}\]     

    D)       \[\frac{\gamma \,PV}{(\gamma -1)}\]

    Correct Answer: C

    Solution :

    Change in internal energy is
    \[\Delta U=\frac{1}{(\gamma -1)}({{P}_{2}}{{V}_{2}}-{{P}_{1}}{{V}_{1}})\]
    Here,     \[{{V}_{1}}=V,\,{{V}_{2}}=2V\]
    \[\therefore \]    \[\Delta U=\frac{1}{\gamma -1}[P\times 2V-P\times V]\]
    \[=\frac{1}{\gamma -1}\times PV\]
    \[=\frac{PV}{\gamma -1}\]
    Note:    The internal energy of an ideal gas depends only on its absolute temperature (T) and is directly proportional to T.


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