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JEE Main & Advanced Physics Thermodynamical Processes Question Bank First Law of Thermodynamics

  • question_answer
    In a thermodynamics process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8J of work is done on the gas. If the initial internal energy of the gas was 30J. The final internal energy will be                                                                 [DPMT 2002]

    A)            18J                                           

    B)             9J

    C)            4.5J                                          

    D)            36J

    Correct Answer: A

    Solution :

                       Given \[\Delta Q=-20J,\] \[\Delta W=-8J\]and \[{{U}_{1}}=30J\]                    \[\Delta Q=\Delta U+\Delta W\]Þ \[\Delta U=(\Delta Q-\Delta W)\] Þ \[({{U}_{f}}-{{U}_{i}})\]= \[({{U}_{f}}-30)=-20-(-8)\] Þ\[{{U}_{f}}=18J\]


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