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CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2002

  • question_answer
    An electron tube was sealed off during manufacture at a pressure of\[1.2\times {{10}^{-7}}mm\]of mercury at\[27{}^\circ C\]. Its volume is 100 cm3. The number of molecules that remain in the tube is:

    A)  \[2\times {{10}^{16}}\]                                

    B)  \[3\times {{10}^{15}}\]

    C)         \[3.86\times {{10}^{11}}\]    

    D)         \[5\times {{10}^{11}}\]

    E)  \[2.5\times {{10}^{12}}\]

    Correct Answer: C

    Solution :

    \[PV=nRT\] \[\Rightarrow \]\[(1.2\times {{10}^{-10}}\times 13.6\times {{10}^{3}}\times 9.8)\times {{10}^{-4}}\]                                 \[=n\times 8.31\times (273+27)\] \[\therefore \]number of moles \[n=6.42\times {{10}^{-13}}\] Hence, number of molecules \[=6.42\times {{10}^{-13}}\times 6.02\times {{10}^{23}}\] \[=3.86\times {{10}^{11}}\]


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