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12th Class Physics Electrostatics & Capacitance Question Bank MCQ - Electrostatic Potential and Capacitance

  • question_answer
    The electric field intensity at a point P due to point charge q kept at point Q is \[24\,N{{C}^{-1}}\]and the electric potential at point P due to same charge is\[12\,J{{C}^{-1}}\]. The order of magnitude of charge q is:

    A) \[{{10}^{-6}}C\]                     

    B) \[{{10}^{-7}}C\]

    C) \[{{10}^{-10}}C\]                   

    D) \[{{10}^{-9}}C\]

    Correct Answer: D

    Solution :

    (d) \[{{10}^{-9}}C\] Electric field of a point charge, \[E=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{{{r}^{2}}}=24N{{C}^{-1}}\] Electric potential of a point charge, \[V=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{r}=12\,J{{C}^{-1}}\] The distance PQ is \[r=\frac{V}{E}=\frac{12}{24}=0.5\,m\] \[\therefore \]Magnitude of charge \[=4\pi {{\varepsilon }_{0}}Vr\] \[=\frac{1}{9\times {{10}^{9}}}\times 12\times 0.5=0.667\times {{10}^{-9}}C\approx {{10}^{-9}}C\]


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