The main function of the commutator in a simple d.c. motor is to

Analyze the question: It asks for the main job of the commutator in a simple d.c. motor.

Concept: In a d.c. motor, a current-carrying coil (armature) sits in a magnetic field. The force on each side of the coil is given by Fleming's left-hand rule, F = BIL.

• When the coil reaches the vertical position (neutral position), the forces would stop turning it. If it kept the same current direction, the coil would flip back and oscillate instead of rotating continuously.
• The commutator is a split-ring connected to the coil ends and touching the carbon brushes. Every half turn, each half of the ring swaps from one brush to the other.
• This reverses the direction of the current in the coil every half revolution. The force on each side of the coil then keeps pushing it in the same rotational direction, giving continuous rotation.

Checking the options:

• A. Letting the armature rotate freely: this is the job of the bearings/shaft, not the commutator.
• B. Increasing flux linkage: this depends on the magnets, the number of turns, and the soft-iron core.
• C. Maintaining a direct current in the armature: the supply is already d.c. The commutator actually makes the current in the coil alternate. (In a generator, the commutator is what converts a.c. to d.c. in the external circuit, which is why this option is a tempting trap.)
• D. Providing a uniform magnetic field: this is done by the magnet pole pieces (often curved).
• E. Reversing the direction of the current in the armature: this is correct.

Tip: Remember "split ring = switch". In a motor, the commutator reverses the coil current every half turn to keep the torque in one direction. In a generator, the same part rectifies the induced a.c. into d.c. in the external circuit. For NECO and JAMB, look at whether the question is about a motor or a generator.