NEET Physics Thermodynamical Processes NEET PYQ-Thermodynamical Processes

  • question_answer
    The efficiency of Carnot engine is 50% and temperature of sink is 500 K. If the temperature of source is kept constant and its efficiency is to be raised to 60%, then the required temperature of the sink will be:                 [AIPMT 2002]

    A)  600 K              

    B)       500 K

    C)  400 K    

    D)                  100 K

    Correct Answer: C

    Solution :

    Efficiency of the Carnot engine is given by
                            \[\eta =1-\frac{{{T}_{2}}}{{{T}_{1}}}\]                                   …(i)
                where    \[{{T}_{1}}=\] temperature of source
                            \[{{T}_{2}}=\] temperature of sink
                Given,   \[\eta =50%\,=0.5,\,\,{{T}_{2}}=500\,K\]
                Substituting in relation (i), we have
                            \[0.5=1-\frac{500}{{{T}_{1}}}\]
                or         \[\frac{500}{{{T}_{1}}}=0.5\]
                \[\therefore \]      \[{{T}_{1}}=\frac{500}{0.5}=1000\,K\]
                Now, the temperature of sink is changed to \[{{T}_{2}}'\] and the efficiency becomes 60% i.e., 0.6.
                Using relation (i), we get
                            \[0.6=1-\frac{T_{2}^{\,'}}{1000}\]
                or         \[\frac{T_{2}^{\,'}}{1000}=1-0.6=0.4\]
                or         \[T_{2}^{\,'}=0.4\times 1000=400K\]
    Note:    Carnot engine is not a practical engine because many ideal situations have been assumed while designing this engine which can practically not be obtained.


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