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

  • question_answer
    Three charges \[Q,\,+q\] and \[+q\] are placed at the vertices of a right-angled isosceles triangle as shown. The net electrostatic energy of the configuration is zero if Q is equal to                                                                                                                                                                              [IIT-JEE (Screening) 2000]

    A)            \[\frac{-q}{1+\sqrt{2}}\]

    B)            \[\frac{-2q}{2+\sqrt{2}}\]

    C)            \[-2q\]

    D)            \[+q\]

    Correct Answer: B

    Solution :

                         Net electrostatic energy \[U=\frac{kQq}{a}+\frac{k{{q}^{2}}}{a}+\frac{kQq}{a\sqrt{2}}=0\] \[\Rightarrow \,\frac{kq}{a}\left( Q+q+\frac{Q}{\sqrt{2}} \right)=0\] Þ \[Q=-\frac{2q}{2+\sqrt{2}}\]


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