Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    A body of specific heat\[0.2\,\,kcal/k{{g}^{o}}C\]is heated through\[{{100}^{o}}C\]. The percentage increase in its mass is

    A) \[9%\]                                  

    B) \[9.3\times {{10}^{-11}}%\]

    C) \[10%\]               

    D)         None of these

    Correct Answer: B

    Solution :

    The surface tension \[(T)\] of a liquid is equal to the work \[(W)\] required to increase the surface area of the liquid film by unity at constant temperature. As per key idea, tension                 \[=\frac{work\,\,done}{surface\,\,area}\] or      \[T=\frac{W}{\Delta \,\,A}\] Since soap bubble has two surface and surface area of soap bubble is\[4\pi {{R}^{2}}\] where\[R\]is radius of bubble. then                      \[W=T\times 2\times 4\pi {{R}^{2}}\] Given                    \[R=2R\] therefore            \[W=T\times 2\times 4\pi \times {{(2R)}^{2}}\]                               \[W=32\pi {{R}^{2}}T\]


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