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A point charge Q is placed inside a cavity within a solid isolated conducting sphere. Consider points A, B and C as shown in the figure, where the magnitudes of the electric fields are $E_A$, $E_B$, $E_C$, respectively. The points B and C are at the same distance from the center of the solid sphere. The correct option is:
Detailed Solution
Inside the cavity, the field at A is due to Q, so $E_A=\frac{kQ}{r^2}\neq0$. Outside, the induced charge +Q spreads uniformly on the outer surface of the sphere, so the field depends only on distance from the centre: $E_B=\frac{kQ}{r_B^2}=\frac{kQ}{r_C^2}=E_C$.