In a direct current (DC) motor, a split-ring commutator is connected to the rotating coil. Which of the following describes the key function of the split-ring commutator?
It reverses the polarity of the external power supply every half turn.
It reverses the direction of the current in the coil every half turn to ensure the turning effect (torque) remains in the same direction.
It maintains a constant direction of current within the coil throughout its entire rotation.
It reverses the direction of the external magnetic field every half turn.
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.