JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Charge and Coulombs Law

  • question_answer
    Two point charges \[+3\mu C\] and \[+8\mu C\] repel each other with a force of \[40N\]. If a charge of \[-5\mu C\]is added to each of them, then the force between them will become                                                               [SCRA 1998; JIPMER 2000]           

    A)                    \[-10N\]                         

    B)                                              \[+10N\]

    C)                    \[+20N\]                                   

    D)                    \[-20N\]

    Correct Answer: A

    Solution :

                         In second case, charges will be \[-\,2\mu C\] and \[+3\mu C\]                    Since \[F\propto {{Q}_{1}}{{Q}_{2}}\] i.e. \[\frac{F}{{{F}'}}=\frac{{{Q}_{1}}{{Q}_{2}}}{Q{{'}_{1}}Q{{'}_{2}}}\]                    \ \[\frac{40}{{{F}'}}=\frac{3\times 8}{-2\times 3}=-4\] Þ \[{F}'=10\,N\](Attractive)


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