Previous Year Question

Correct answer: D — Flemming’s Right hand rule

Applying Fleming’s right-hand rule

When a conductor moves across a magnetic field, charges in it experience a magnetic force. The resulting charge separation produces a motional EMF. Fleming’s right-hand rule relates the direction of conductor motion, magnetic field and induced EMF/current in generator action.

Hold the thumb, first finger and middle finger of the right hand mutually perpendicular. Point the first finger in the magnetic-field direction, from north to south outside the magnet. Point the thumb in the direction of conductor motion. The middle finger then indicates the direction of induced conventional current if the circuit is closed.

For a rotating coil, apply the rule to each active conductor side using that side’s direction of motion and the local field direction. Their induced EMFs combine according to the coil connection. An open circuit can have induced EMF even though no sustained current flows.

For electromagnetic induction more generally, Lenz’s law determines the opposing sense of the induced effect, including cases with changing flux but no conductor motion. Faraday’s law, e = −N dΦ/dt, includes this opposition through its minus sign. The named hand rule expected by the paper is Fleming’s right-hand rule for generator action.