Commutator enables continuous rotation in DC motors

Steps:

• Recall that a DC motor requires current reversal in the coil to maintain torque direction.
• Identify components: armature rotates, brushes contact, slip rings provide continuous connection, split-ring commutator switches connections.
• Analyze function: reversal occurs at half rotations to keep magnetic field interaction consistent.
• Match to choice: only split-ring commutator physically reverses current via its split design.

Why D is correct:

• The split-ring commutator, by design, inverts the current direction in the coil every half rotation, ensuring unidirectional torque per Fleming's left-hand rule.

Why the others are wrong:

• A. The armature is the rotating coil itself, not the reversing mechanism.
• B. The brushes maintain electrical contact but do not reverse current.
• C. Slip rings allow continuous AC-like connection without reversal, used in AC motors.

Final answer: D