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

  • question_answer
    At a point 20 cm from the centre of a uniformly charged dielectric sphere of radius 10 cm, the electric field is 100 V/m. The electric field at 3 cm from the centre of the sphere will be                                   [BCECE 2005]

    A)            150 V/m

    B)                                      125 V/m

    C)            120 V/m

    D)                                      Zero

    Correct Answer: C

    Solution :

                         Electric field outside of the sphere \[{{E}_{out}}=\frac{kQ}{{{r}^{2}}}\]         ...(i) Electric field inside the dielectric sphere \[{{E}_{in}}=\frac{kQx}{{{R}^{3}}}\]...(ii) From (i) and (ii),  \[{{E}_{in}}={{E}_{out}}\times \frac{{{r}^{2}}x}{R}\] Þ At 3 cm,  \[E=100\times \frac{3\,{{(20)}^{2}}}{{{10}^{3}}}=120\,V/m\]


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