NEET Physics Thermodynamical Processes NEET PYQ-Thermodynamical Processes

  • question_answer
    An ideal gas heat engine operates in Carnot cycle between \[227{}^\circ C\] and \[127{}^\circ C\]. It absorbs \[6\times {{10}^{4}}\,\text{cal}\] of heat at higher temperature. Amount of heat converted to work is:   [AIPMT (S) 2005]

    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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