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CMC Medical CMC-Medical VELLORE Solved Paper-2010

  • question_answer
    The p-V diagram of a system undergoing thermodynamic transformation is shown is figure. The work done by the system in going from A\[\to \]B\[\to \]C is 50 J and 20 cal heat is given to the system. The change in internal a energy between A and C is

    A)  34 J                                       

    B)  70 J

    C)  84 J                                       

    D)  134 J

    E)  None of these

    Correct Answer: A

    Solution :

                    From the first law of thermodynamics, if an amount of heat Q is given to a system, a part of it will be used in increasing the internal energy \[(\Delta U)\]of the system and rest in doing work (W) by the system. Therefore, \[Q=\Delta U+W\] \[\Rightarrow \]                               \[\Delta U=Q-W\] Given, \[Q=20\,cal=20\times 4.2J=84\,J\] \[W=50\,J\] \[\therefore \]  \[\Delta U=(84-50)J=34\,J\]


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