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DUMET Medical DUMET Medical Solved Paper-2002

  • question_answer
    In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas was 30 J, the final internal energy will be:

    A)  18 J           

    B)  9 J

    C)  4.5 J           

    D)  36 J

    Correct Answer: A

    Solution :

    Key Idea: Energy remains conserved in the process according to first law of thermodynamics. When 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 the rest in doing work (W) by the system, hence \[Q=\Delta U+W\] Heat released by system \[Q=-20\,J\] Work done on the gas \[W=-8\,J\] \[\therefore \] \[\Delta U=Q-W\] \[=-20-(-8)\] \[=-12\,J\] Final internal energy \[{{U}_{f}}={{U}_{i}}+\Delta U=30-12=18\,J\].


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