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A neutral spherical metallic conductor has a spherical cavity. A positive point charge sits at the centre of the cavity, and another positive point charge is placed outside the conductor. Match each cause in Column-I with the effects it produces in Column-II. Column-I (Cause): (A) The outside charge is moved to a new position. (B) The inside (cavity) charge is moved to a new position within the cavity. (C) The magnitude of the charge inside the cavity is increased. (D) The conductor is earthed. Column-II (Effect): (P) The charge distribution on the inner surface of the cavity changes. (Q) The charge distribution on the outer surface of the conductor changes. (R) The electric potential at the centre due to the charges on the outer surface changes. (S) The force on the charge inside the cavity changes. Which single option lists effects that genuinely occur for the matched causes overall?

1. (P), (Q), (R) and (S)
2. (P), (Q) and (S) only
3. (Q), (R) and (S) only
4. (P), (R) and (S) only

Correct answer: (P), (Q), (R) and (S)

Solution

Electrostatic shielding decouples inside and outside. (A) Moving the outside charge changes outer-surface distribution (Q) and the potential at the centre from outer charges (R); it does not change the inner cavity field or the force on the inside charge. (B) Moving the inside charge changes the inner-surface induced distribution (P) and the force on the inside charge (S). (C) Increasing the inside charge changes inner-surface (P), outer-surface (Q) and potentials (R). (D) Earthing changes the outer surface charge (Q) and potential (R). Across all causes, every effect (P), (Q), (R) and (S) is produced, so the inclusive option is correct.

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