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JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Electric Field and Potential

  • question_answer
    A pendulum bob of mass \[30.7\times {{10}^{-6}}\,kg\] and carrying a charge \[2\times {{10}^{-8}}\,C\] is at rest in a horizontal uniform electric field of 20000 V/m. The tension in the thread of the pendulum is \[(g=9.8\,m/{{s}^{2}})\]                                                                      [UPSEAT 2004]

    A)                    \[3\times {{10}^{-4}}\,N\]

    B)                                      \[4\times {{10}^{-4}}\,N\]

    C)                    \[5\times {{10}^{-4}}\,N\]

    D)                                      \[6\times {{10}^{-4}}\,N\]

    Correct Answer: C

    Solution :

                         \[T=\sqrt{{{(mg)}^{2}}+{{(QE)}^{2}}}\] \[=\sqrt{{{(30.7\times {{10}^{-6}}\times 9.8)}^{2}}+{{(2\times {{10}^{-8}}\times 20000)}^{2}}}\]\[=5\times {{10}^{-4}}N\]


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