A bar magnet is placed near and lying along the axis of a solenoid connected to a galvanometer. The pointer of the galvanometer shows no deflection when?

1. Analyze the question A bar magnet lies along the axis of a solenoid that is connected to a galvanometer. We need to find when the galvanometer pointer shows no deflection, meaning no current is flowing.

2. The concept: Faraday's law of electromagnetic induction An EMF (and so a current in a closed circuit) is induced in a coil only when the magnetic flux linking the coil changes.

EMF = -N (ΔΦ/Δt)

• If the flux changes, ΔΦ ≠ 0, so there is an induced EMF and the galvanometer deflects.
• If the flux does not change, ΔΦ = 0, so there is no EMF and no deflection.

Flux through the solenoid changes only when there is relative motion between the magnet and the solenoid. It makes no difference which one moves.

3. Check each option

• A. The magnet moves towards the solenoid. The flux increases, so the pointer deflects.
• B. There is no relative motion. The flux is constant, so there is no induced EMF and no deflection.
• C. The magnet moves away. The flux decreases, so the pointer deflects (in the opposite direction to A).
• D. The solenoid moves away from the magnet. There is relative motion, so the flux changes and the pointer deflects.

4. Answer

5. Exam tip Remember: "No change in flux, no induced current." A steady magnet, even a strong one, induces nothing in a coil. Only relative motion (or a changing current in a nearby coil) produces induction. In JAMB questions like this, look for the option that says "no relative motion" or "constant flux" when the question asks about zero deflection.