J & K CET Engineering J and K - CET Engineering Solved Paper-2006

  • question_answer
    Two identical spheres with charges \[4q,-2q\] kept some distance apart exert a force F on each other. If they are made to touch each other and replaced at their old positions, the force between them will be

    A)  \[\frac{1}{9}F\]          

    B)  \[\frac{1}{8}F\]

    C)  \[\frac{9}{8}F\]

    D)  \[\frac{8}{9}F\]

    Correct Answer: B

    Solution :

    When spheres are touched and separated, charge is \[q'=\frac{4q-2q}{2}=\frac{2q}{2}=q\] From Coulomb's law \[F=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{(4a)-(-2q)}{r}\] ?..(i) When made to touch \[F'=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{{{q}^{2}}}{r}\] ??(ii) From Eqs. (i) and (ii), we get \[F'=\frac{F}{8}\]


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