RAJASTHAN ­ PET Rajasthan PET Solved Paper-2001

  • question_answer
    Twenty seven drops of water of the same size are equally potential V. They are then united to form a bigger drop. By what factor will the electrical potential changes?

    A)  9V

    B)  3V

    C)  27V            

    D)  \[\frac{1}{3}V\]

    Correct Answer: A

    Solution :

     Suppose the radius of small drop is r and charge is q and the radius of big drop is R and charge is Q. Then \[\frac{4}{3}\pi {{R}^{3}}=27.\frac{4}{3}\pi {{r}^{3}}\] \[\Rightarrow \] \[R=3r\] Potential at small drop \[V=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{r}\] \[\therefore \]Potential at big drop\[V'=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{Q}{R}\] \[=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{27q}{3r}\] \[=9V\]


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