DC Machines is one of 9 topics in the Grade 11 Electrical Technology CAPS syllabus, covered across 3 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. What is the key difference between a generator and a motor?
A generator converts mechanical energy to electrical energy; a motor converts electrical energy to mechanical energy
A generator and a motor perform identical energy conversions
A motor only works on AC supply, never DC
A generator has no rotating parts, unlike a motor
Answer: A generator converts mechanical energy to electrical energy; a motor converts electrical energy to mechanical energy — A generator converts mechanical energy (input) into electrical energy (output), while a motor converts electrical energy (input) into mechanical energy (output).
Easy
2. What is the function of the commutator in a DC machine?
To reverse the connection to the external circuit at the correct moment, converting induced AC to DC output (or maintaining correct current direction in a motor)
To provide mechanical support for the entire machine frame
To produce the main magnetic field
To measure the machine's rotational speed
Answer: To reverse the connection to the external circuit at the correct moment, converting induced AC to DC output (or maintaining correct current direction in a motor) — The commutator reverses the connection to the external circuit at the correct moment during rotation, converting alternating induced current into unidirectional DC output in a generator, or maintaining correct current direction for continuous torque in a motor.
Medium
3. Name the stationary conducting contacts that press against the rotating commutator to provide electrical connection to the armature.
Answer: brushes — Brushes are the stationary conducting contacts (commonly carbon or graphite) that press against the rotating commutator, providing the sliding electrical connection to the armature windings.
