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DUMET Medical DUMET Medical Solved Paper-2004

  • question_answer
    In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out 30 J of heat and 10 J of work is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be:

    A)  30 J           

    B)  20 J

    C)  60 J          

    D)  40 J

    Correct Answer: B

    Solution :

     Key Idea: Energy remains conserved in the process according to first law of thermodynamics. If an amount of heat Q is given to a system, a part of it is used in increasing the internal energy \[(\Delta U)\] of the system and the rest in doing work (W) by the system. Hence, we have \[Q=\Delta \,U+W\] (first law of thermodynamics) Given, \[Q=-30\,J,\,W=-10\,J\] \[\therefore \] \[\Delta U=-30+10=-20\,J\] \[\Rightarrow \] \[{{U}_{f}}=-{{U}_{i}}=-20\,J\] \[\Rightarrow \] \[{{U}_{f}}-40=-20\] \[\Rightarrow \] \[{{U}_{f}}=40-20=20\,J\]


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