J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    A certain quantity of heat energy is given to a diatomic ideal gas which expands at constant pressure. The fraction of the heat energy that is converted into work is

    A)  \[2/3\]           

    B)  \[2/7\]

    C)  \[1/5\]           

    D)  \[1/7\]

    Correct Answer: B

    Solution :

    According to first law of thermodynamics \[\Delta Q=\Delta U+\Delta W\] \[\Rightarrow \] \[{{C}_{V}}\Delta T={{C}_{p}}\Delta T+W\] or \[W=({{C}_{P}}-{{C}_{V}})\Delta T\] \[=\left( \frac{7}{2}-\frac{5}{2} \right)\Delta T\] Now, \[\frac{W}{Q}=\frac{\left( \frac{7}{2}-\frac{5}{2} \right)\Delta T}{\frac{7}{2}\Delta T}\] \[=\frac{2}{7}\]


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