Manipal Engineering Manipal Engineering Solved Paper-2011

  • question_answer
    A charge of \[{{10}^{-9}}\] C is placed on each of the 64 identical drops of radius 2 cm. They are then combined to form a bigger drop. Its potential will be

    A) \[7.2\times {{10}^{3}}V\]                             

    B) \[7.2\times {{10}^{2}}V\]

    C) \[1.44\times {{10}^{2}}V\]          

    D)         \[1.44\times {{10}^{3}}V\]

    Correct Answer: A

    Solution :

    Volume of bigger drop = volume of 64 small drops \[ie,\]    \[\frac{4}{3}\pi {{R}^{3}}=64\times \frac{4}{3}\pi {{r}^{3}}\] or            \[R=4r\] Potential on small drop                 \[{{V}_{1}}=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{r}\] Potential on bigger drop                 \[{{V}_{2}}=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{64q}{R}\]                 \[{{V}_{2}}=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{64q}{4r}\]                 \[=\frac{9\times {{10}^{9}}\times 64\times {{10}^{-9}}}{4\times 2\times {{10}^{-2}}}\]                 \[=7.2\times {{10}^{3}}V\]


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