JEE Main & Advanced Physics Electrostatics & Capacitance JEE PYQ-Electrostatics and Capacitance

  • question_answer
    The energy stored in the electric field produced by a metal sphere is 4.5 J. If the sphere contains \[4\mu C\] charge, its radius will be: [Take :\[\frac{1}{4\pi {{\varepsilon }_{0}}}=9\times {{10}^{9}}N-{{m}^{2}}/{{C}^{2}}\]] [JEE Online 08-04-2017]

    A) 32 mm

    B) 16 mm

    C) 28 mm

    D) 20 mm

    Correct Answer: B

    Solution :

    [b] Energy of sphere\[=\frac{{{Q}^{2}}}{2C}\]
                \[4.5=\frac{16\times {{10}^{-12}}}{2C}\]
                \[C=\frac{16\times {{10}^{-12}}}{9}=4\pi {{\varepsilon }_{0}}R\]
                \[R=\frac{16\times {{10}^{-12}}}{9}\times \frac{1}{4\pi {{\varepsilon }_{0}}}\]
                \[=9\times {{10}^{9}}\times \frac{16}{9}\times {{10}^{-12}}\]
                \[=16\times {{10}^{-3}}=16mm\]


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