A simple d.c. motor consists of a coil positioned between magnetic poles. A split-ring commutator connects the d.c. power supply to the coil.
What is the function of the split-ring commutator in this motor?
It reverses the direction of the external magnetic field every half-turn (180∘180^\circ180∘) of the coil.
It reverses the direction of the current in the coil every half-turn (180∘180^\circ180∘) to ensure continuous rotation in the same direction.
It converts direct current (d.c.) from the supply into high-frequency alternating current (a.c.) to increase the motor's speed.
It disconnects the current permanently once the coil reaches its maximum rotational speed.
275 exam-style questions on CIE IGCSE Physics 4.5 Electromagnetic effects, covering 4.5.1a Electromagnetic induction, 4.5.1b Direction of an induced e.m.f., 4.5.2 The a.c. generator, 4.5.3a Magnetic effect of a current and its applications, 4.5.3b Strength and direction of the field around wires and solenoids, 4.5.4a Force on a current-carrying conductor, 4.5.4b Force on beams of charged particles, 4.5.5 The d.c. motor, 4.5.6a Construction and operation of a transformer, 4.5.6b Turns ratio and current in a transformer, and 4.5.6c High-voltage transmission of electricity. Each one has a worked solution and a mark scheme showing where the marks go.