Haryana PMT Haryana PMT Solved Paper-2010

  • question_answer
    A gas expands with temperature according to the relation \[V=K{{T}^{2/3}}.\] what is the work done when the temperature changes by 30°C?

    A)  10 R                                      

    B)  20 R

    C)  30 R                                      

    D)  40 R

    Correct Answer: B

    Solution :

                    \[W=\int{\rho dV=\int{\frac{RT}{V}\,\,dV}}\] Since,                    \[V=K{{T}^{2/3}}\] \[\Rightarrow \]                               \[dV=\frac{2}{3}K{{T}^{-1}}dT\] Eliminating K, we find \[\frac{dV}{V}=\frac{2}{3}\frac{dT}{T}\] Hence, \[W=\int_{{{T}_{1}}}^{{{T}_{2}}}{\frac{2}{3}\,\frac{RT}{T}dT}\]                 \[=\frac{2}{3}R({{T}_{2}}-{{T}_{1}})\]                 \[=\frac{2}{3}R(30)=20R\]


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