RAJASTHAN PMT Rajasthan - PMT Solved Paper-2006

  • question_answer
    If n drops of potential V merge, find new potential on the big drop.

    A)  \[{{n}^{2/3}}V\]                              

    B)  \[{{n}^{1/3}}V\]

    C)  \[nV\]                 

    D)         \[{{V}^{n/3}}\]

    Correct Answer: A

    Solution :

    Volume of big drop\[=n\] \[\times \] volume of a small drop \[\Rightarrow \]               \[\frac{4}{3}\pi {{R}^{3}}=n\frac{4}{3}\pi {{r}^{3}}\] \[\Rightarrow \]               \[R={{n}^{1/3}}r\]                                            ... (i) Potential of small drop  \[V=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{r}\] \[\Rightarrow \]               \[q=V4\pi {{\varepsilon }_{0}}r\]                                               ... (ii) So, potential of big drop\[=\frac{1}{4\pi {{\varepsilon }_{0}}}\times \frac{nq}{R}\] \[\Rightarrow \]               \[V=\frac{4\pi {{\varepsilon }_{0}}\times V\times r}{4\pi {{\varepsilon }_{0}}\times {{n}^{1/3}}r}={{n}^{2/3}}V\]


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