Identifying the split-ring commutator in a DC motor

Steps:

• Recall that a simple DC motor has a coil (armature) rotating in a magnetic field to produce torque.
• Note that DC motors require current direction to reverse every half rotation for continuous motion.
• Identify Q as the component connecting the power source to the coil while allowing rotation and current reversal.
• Confirm Q matches the split-ring commutator, which has a gap to swap connections.

Why D is correct:

• The split-ring commutator reverses current in the coil every half turn, ensuring torque remains in one direction per Fleming's left-hand rule.

Why the others are wrong:

• A: The coil is the armature wound with wire, not a connecting device.
• B: The magnet provides the fixed magnetic field, stationary in the diagram.
• C: Slip rings provide continuous electrical contact without reversal, used in AC motors.

Final answer: D