KVPY Sample Paper KVPY Stream-SX Model Paper-20

  • question_answer
    For an ideal gas, let \[{{C}_{P}}=\alpha +cT\] and \[{{C}_{V}}=b+cT.\]  where, a, b and c are constants. T-V relation that holds in adiabatic expansion is

    A) \[{{V}^{a-b}}.{{T}^{b}}.{{e}^{cT}}=\text{constant}\]

    B) \[{{T}^{a-b}}.{{V}^{b}}.{{e}^{cT}}=\text{constant}\]

    C) \[{{T}^{a-b}}.{{V}^{a}}.{{e}^{cT}}=\text{constant}\]

    D) \[{{V}^{a-b}}.{{T}^{a}}.{{e}^{cT}}=\text{constant}\]

    Correct Answer: A

    Solution :

    For adiabatic process, \[\Delta Q=\Delta U=\Delta W=0\]
    \[\therefore \,\,\,\,{{C}_{V}}dT+pdV=0\]\[\Rightarrow \,\,{{C}_{V}}dT+\frac{RT}{V}.dV=0\]\[\Rightarrow \,\,{{C}_{V}}dT+\left( {{C}_{p}}-{{C}_{v}} \right)T.\frac{dV}{V}=0\]
    \[\left( b+cT \right)dT+\left( a-b \right)T.\frac{dV}{V}=0\]\[=b\frac{dT}{T}+cdT+\left( a-b \right)\frac{dV}{V}=0\]
    Integrating above equation, we have
    \[b\ln T+cT+\left( a-b \right)InV=a\] constant So,\[ln\,\,{{T}^{b}}+cT+\ln \,{{V}^{a-b}}=a\] constant\[\Rightarrow \,\,\,{{V}^{a-b}}.{{T}^{b}}.{{e}^{cT}}=cons\tan t\]


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