Which of the following is NOT part of an a.c generator?

Analyze the question You are asked to pick the component that does NOT belong to an a.c. generator (alternator).

Explain the concept An a.c. generator works by rotating a coil (armature) in a magnetic field, which induces an e.m.f. by electromagnetic induction. Its main parts are:

• Field magnet: produces the magnetic field.
• Armature: the coil that rotates and in which the e.m.f. is induced.
• Slip rings: two continuous rings connected to the ends of the coil. They keep the same connection to the external circuit throughout rotation, so the output stays alternating.
• Carbon brushes: press against the slip rings and carry current to the external circuit.

A commutator (split-ring) is different. It reverses the connections every half turn, so the output current flows in one direction. This is the feature of a d.c. generator (or d.c. motor).

Step-by-step check

• A. Commutator: belongs to a d.c. machine, not an a.c. generator.
• B. Armature: part of an a.c. generator.
• C. Field magnet: part of an a.c. generator.
• D. Carbon brushes: part of an a.c. generator.
• E. Slip rings: part of an a.c. generator.

Answer The commutator is the odd one out, which is A.

Exam tip Remember: Slip rings = AC, Split ring (commutator) = DC. If you see "commutator" in a question about a.c. generators, it is almost always the answer to a "NOT part of" question.