When current flows through a moving-coil galvanometer, the force exerted on the pointer depends on the: i…

Analyze the question: We need to decide which factors affect the force (and so the deflecting torque) in a moving-coil galvanometer when current flows.

Concept: A current-carrying conductor in a magnetic field experiences a force:

F = B I L

(more precisely, for a coil of N turns, F = N B I L)

Where:

• B = magnetic field strength (flux density)
• I = current
• L = length of the conductor (the length of the coil's sides in the field)

Check each statement:

• i. Strength of the current: F is directly proportional to I. Correct.
• ii. Magnetic field strength: F is directly proportional to B. Correct.
• iii. Length of the coil: F is directly proportional to L (the effective length of wire in the field, which grows with the length and the number of turns). Correct.

All three factors appear in the formula F = BIL, so all three statements are correct.

Answer: Option D, i, ii and iii.

Tip: If a question asks what affects the force on a current-carrying conductor in a magnetic field, think of F = BIL. Every quantity in the formula (B, I, L, plus N for a coil, and sin θ for the angle) matters. In a galvanometer, the radial magnetic field keeps the angle at 90°, so the force depends directly on those quantities.