BHU PMT BHU PMT (Mains) Solved Paper-2008

  • question_answer
    A liquid drop of radius R breaks into 64 tiny drops each of radius r. If the surface tension of the liquid is. T, then the gain in energy is

    A) \[48\pi {{R}^{2}}T\]        

    B) \[12\pi {{r}^{2}}T\]

    C) \[96\pi {{R}^{2}}T\]                        

    D) \[192\pi {{r}^{2}}T\]

    Correct Answer: D

    Solution :

                     Volume of big drop \[=64\times volume\text{ }of\text{ }tiny\text{ }drops\] Or           \[\frac{4}{3}\pi {{R}^{3}}=64\times \frac{4}{3}\pi {{r}^{3}}\] Or        \[R=4r\] So, the gain in surface energy = work done in splitting a liquid drop of radius R into n identical drops \[=4\pi T{{R}^{2}}({{n}^{1/3}}-1)\] \[=4\pi T{{(4r)}^{2}}({{64}^{1/3}}-1)=192\,\pi {{r}^{2}}T\]


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