J & K CET Medical J & K - CET Medical Solved Paper-2005

  • question_answer
    If eight similar charge drops combine to form a bigger drop, then the ratio of capacitance of bigger drop to that of smaller drop will be :

    A)  2 : 1                                      

    B)  8:1

    C)  4:1                                        

    D)  16 : 1

    Correct Answer: A

    Solution :

                     Let radius of big drop be R and of smaller be r. Then, volume of bigger drop\[=8\times \]volume of single drop Also, since shape of drop is assumed spherical, volume of a sphere of radius a is\[\frac{4}{3}\pi {{a}^{3}}\]. \[\therefore \]  \[\frac{4}{3}\pi {{R}^{3}}=8\times \frac{4}{3}\pi {{r}^{3}}\] \[\Rightarrow \]               \[R=2r\] Capacitance of a sphere of radius a is \[C=4\pi {{\varepsilon }_{0}}a\] \[\therefore \]Capacitance of big drop \[C=4\pi {{\varepsilon }_{0}}R\] Capacitance of small drop                 \[C=4\pi {{\varepsilon }_{0}}(2r)\] \[\therefore \]  \[\frac{C}{C}=\frac{4\pi {{\varepsilon }_{0}}(2r)}{4\pi {{\varepsilon }_{0}}\,r}=\frac{2}{1}\]


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