BVP Medical BVP Medical Solved Paper-2002

  • question_answer The radius of a soap bubble is R and surface tension is T, keeping the temperature constant, the extra energy needed to double the radius of the soap bubble by blowing, will be:

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

    B)  \[24\pi {{R}^{2}}T\]

    C)  \[16\pi {{R}^{2}}T\]                       

    D)  \[8\pi {{R}^{2}}T\]

    Correct Answer: B

    Solution :

    Energy needed to double the radius \[E=T.2\Delta A\] \[=T.2\left\{ 4\pi r_{2}^{2}-4\pi r_{1}^{2} \right\}\] \[=T.2\times 4\pi \{r_{2}^{2}-r_{1}^{2}\}\] \[=T.2\times 4\pi \{{{(2R)}^{2}}-{{(R)}^{2}}\}\] \[=8\pi T.\{4{{R}^{2}}-{{R}^{2}}\}\] \[=24\pi {{R}^{2}}T\]

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