Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    The radius\[R\]of the soap bubble is doubled under isothermal condition. If\[T\]be the surface tension of soap bubble, the work done in doing so is given by

    A) \[32\pi {{R}^{2}}T\]                        

    B) \[24\pi {{R}^{2}}T\]

    C) \[8\pi {{R}^{2}}T\]                           

    D) \[4\pi {{R}^{2}}T\]

    Correct Answer: A

    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            \[W=T\times 2\times 4\pi \times {{(2R)}^{2}}\]                               \[W=32\pi {{R}^{2}}T\]


You need to login to perform this action.
You will be redirected in 3 sec spinner