Split-Ring Commutator in DC Motors

Steps:

• Recognize the device reversing current direction in a DC motor as a split-ring commutator.
• Distinguish from slip rings, which maintain current direction in AC generators.
• Identify reversal timing: occurs when the coil's plane is parallel to the magnetic field for maximum torque.
• Select option matching split ring and parallel orientation.

Why D is correct:

• Split-ring commutator reverses current precisely when the coil plane is parallel to the magnetic field, maintaining unidirectional torque via Fleming's left-hand rule.

Why the others are wrong:

• A: Slip rings do not reverse current; parallel orientation irrelevant for AC use.
• B: Slip rings suit AC, not reversal; perpendicular plane misaligns with torque maximum.
• C: Split ring correct but perpendicular plane delays reversal, halting rotation.

Final answer: D