CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2004

  • question_answer
    A spherical drop of capacitance \[1\,\mu F\] is broken into eight drops of equal radius. Then, the capacitance of each small drop is:

    A)  \[\frac{1}{2}\mu F\]                      

    B)  \[\frac{1}{4}\mu F\]

    C)  \[\frac{1}{8}\mu F\]                      

    D)  \[8\,\mu F\]

    Correct Answer: A

    Solution :

    Let R and r be the radii of bigger and each smaller drop respectively. \[\Rightarrow \]               \[\frac{4}{3}\pi \,{{R}^{3}}=8\times \frac{4}{3}\pi {{r}^{3}}\]                        \[\Rightarrow \]               \[R=2r\]                                                               ... (1) The capacitance of a smaller spherical drop is                 \[C=4\pi \,{{\varepsilon }_{0}}r\]                                              ... (2) The capacitance of bigger drop is                 \[C=4\,\pi \,{{\varepsilon }_{0}}\,R\]                 \[=2\times 4\,\pi \,{{\varepsilon }_{0}}\,r\]                          \[(\because \,R=2r)\]                 = 2C                                       [from eq (2)] \[\therefore \]  \[C=\frac{C}{2}\]                 \[=\frac{1}{2}\mu F\]                     \[(\because \,C=1\,\mu \,F)\]


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