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Railways NTPC (Technical Ability) Thermodynamics Question Bank Thermodynamics

  • question_answer
    A cyclic heat engine receives 600 kJ of heat from a 1000 K source and rejects 450 kJ to a 300 K sink. The quantity \[\oint{\frac{\delta Q}{T}}\] and efficiency of the engine are respectively:

    A) 2.1 kJ/K and 70%  

    B) \[-\,\,0.9\] kJ/K and 25%

    C) \[+\,\,0.9\] kJ/K and 70%

    D) \[-\,\,2.1\] kJ/K and 50%

    Correct Answer: B

    Solution :

    \[\oint{\frac{d\,Q}{T}}=\frac{{{Q}_{1}}}{{{T}_{1}}}-\frac{{{Q}_{2}}}{{{T}_{2}}}=\frac{600}{1000}-\frac{450}{300}=-\,\,0.9\,\text{kJ/K}\] \[\eta =1-\frac{{{Q}_{2}}}{{{Q}_{1}}}=1-\frac{450}{600}=0.25\,\,or\,\,25%\]


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