In a simple d.c. motor, a split-ring commutator is connected to the coil to ensure that it continues to rotate in the same direction.
How does the split-ring commutator achieve this?
By reversing the direction of the current in the coil every half turn.
By maintaining a constant direction of current in the coil throughout the full rotation.
By reversing the polarity of the permanent magnetic field every half turn.
By varying the potential difference across the brushes during rotation.
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.