NEET Physics Thermodynamical Processes NEET PYQ-Thermodynamical Processes

  • question_answer
    An engine has an efficiency of \[\frac{1}{6}\]. When the temperature of sink is reduced by \[62{}^\circ C,\] its efficiency is doubled.  Temperature of the source is :                                             [AIPMT (S) 2007]

    A)  \[124{}^\circ C\]

    B)                  \[37{}^\circ C\]

    C)  \[62{}^\circ C\]     

    D)                  \[99{}^\circ C\]

    Correct Answer: D

    Solution :

    Efficiency of engine is given by
                            \[\eta =1-\frac{{{T}_{2}}}{{{T}_{1}}}\]
    \[\therefore \]      \[\frac{{{T}_{2}}}{{{T}_{1}}}=1-\eta =1-\frac{1}{6}=\frac{5}{6}\]                 …(i)
                In other case,
                            \[\frac{{{T}_{2}}-62}{{{T}_{1}}}=1-\eta =1-\frac{2}{6}=\frac{2}{3}\] …(ii)
                Using Eq. (i),
                            \[{{T}_{2}}-62=\frac{2}{3}\,{{T}_{1}}=\frac{2}{3}\times \frac{6}{5}{{T}_{2}}\]
    or         \[\frac{1}{5}{{T}_{2}}=62\]
    \[\therefore \]      \[{{T}_{2}}=310\,K\,=310-{{273}^{o}}C\]
                            \[={{37}^{o}}C\]
                Hence,   \[{{T}_{1}}=\frac{6}{5}{{T}_{2}}=\frac{6}{5}\times 310\]
                            \[=\text{ }372\,K\]
                            \[=372-273\]
                            \[=99{}^\circ C\]
                Hence, temperature of source is \[99{}^\circ C\].


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