JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Capacitance

  • question_answer
    The diameter of each plate of an air capacitor is \[4cm\]. To make the capacity of this plate capacitor equal to that of \[20cm\] diameter sphere, the distance between the plates will be                                                         [MP PET 1996]

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

    B)            \[1\times {{10}^{-3}}m\]

    C)                    \[1cm\]                           

    D)            \[1\times {{10}^{-3}}cm\]

    Correct Answer: B

    Solution :

               Capacity of spherical conductor of 20 cm diameter \[{{C}_{1}}=4\pi {{\varepsilon }_{0}}r=4\pi {{\varepsilon }_{0}}\times 10\] Capacity of parallel plate air capacitor \[{{C}_{2}}=\frac{{{\varepsilon }_{0}}A}{d}=\frac{{{\varepsilon }_{0}}[\pi {{(2)}^{2}}]}{d}=\frac{{{\varepsilon }_{0}}\times 4\pi }{d}\] Hence \[{{C}_{1}}={{C}_{2}}\] Þ \[40\pi {{\varepsilon }_{0}}=\frac{4\pi {{\varepsilon }_{0}}}{d}\]Þ \[d={{10}^{-3}}m\]


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