In a simple d.c. generator, a coil is rotated at a constant rate in a uniform magnetic field. A split-ring commutator connects the rotating coil to the external circuit. What is the function of this split-ring commutator?
to reverse the direction of the induced e.m.f. inside the coil every half revolution
to convert the alternating e.m.f. induced in the coil into a unidirectional e.m.f. across the external circuit
to ensure the current inside the rotating coil always flows in a single, constant direction
to prevent any induced e.m.f. when the plane of the coil is perpendicular to the magnetic field
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.