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12th Class Physics Electrostatics & Capacitance Question Bank Case Based (MCQs) - Electrostatic Potential and Capacitance

  • question_answer
    If a parallel plate air capacitor consists of two circular plates of diameter 8 cm. At what distance should the plate be held so as to have the same capacitance as that of sphere of diameter 20 cm?                         

    A) 9 mm                           

    B) 4 mm     

    C) 8 mm                           

    D) 2 mm

    Correct Answer: B

    Solution :

    (b) 4 mm As,        \[\frac{{{\varepsilon }_{0}}A}{d}=4\pi {{\varepsilon }_{0}}R\] Or \[\frac{{{\varepsilon }_{0}}\pi {{D}^{2}}}{4d}=4\pi {{\varepsilon }_{0}}R\] Or \[d=\frac{{{D}^{2}}}{16R}=\frac{{{\left( 0.08 \right)}^{2}}}{16\times 0.10}=4\times {{10}^{-3}}m=4\,mm\]


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