NEET AIPMT SOLVED PAPER SCREENING 2005

  • question_answer
                    An ideal gas heat engine operates in Carnot cycle between \[{{227}^{\text{o}}}C\] and \[{{127}^{\text{o}}}C\]. It absorbs \[6\times {{10}^{4}}\] cal of heat at higher temperature. Amount of heat converted to work is:                                                       

    A)                 \[2.4\times {{10}^{4}}\,cal\]       

    B)                 \[6\times {{10}^{4}}\,cal\]           

    C)                 \[1.2\times {{10}^{4}}\,cal\]       

    D)                 \[4.8\times {{10}^{4}}\,cal\]

    Correct Answer: C

    Solution :

                    Key Idea: The heat converted to work is the amount of heat that remains after going through sink.                 From the relation                 \[\frac{{{Q}_{2}}}{{{Q}_{1}}}=\frac{{{T}_{2}}}{{{T}_{1}}}\]                         \[Given,{{Q}_{1}}=6\times {{10}^{4}}\,cal,\]                 \[{{T}_{1}}=227+273=500\,K\]                 \[{{T}_{2}}=127+273=400\,K\] \[\therefore \frac{{{Q}_{2}}}{6\times {{10}^{4}}}=\frac{400}{500}\] \[\Rightarrow {{Q}_{2}}=\frac{4}{5}\times 6\times {{10}^{4}}\]                 \[=4.8\times {{10}^{4}}\,cal\]                 Now, heat converted to work                 \[={{Q}_{1}}-{{Q}_{2}}\]                 \[=6.0\times {{10}^{4}}-4.8\times {{10}^{4}}\]                 \[=1.2\times {{10}^{4}}\,cal\]                 Note:    Carnot cycle consists of following four stages:                 (i) Isothermal expansion                 (ii) Adiabatic expansion                 (iii) Isothermal compression                 (iv) Adiabatic compression                 After doing the calculations for different processes, we achieve the reaction                 \[\frac{{{Q}_{2}}}{Q{{ & }_{1}}}=\frac{{{T}_{2}}}{{{T}_{1}}}\]


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