A student turns the handle of a simple alternating current (a.c.) generator, causing a rectangular coil to rotate between the north and south poles of a permanent magnet.
Explain, in terms of magnetic fields, how the rotation of the coil produces an alternating electromotive force (e.m.f.) across its output terminals.
State the position of the rotating coil relative to the magnetic field when the magnitude of the alternating output voltage is zero, and explain why the voltage is zero at this position.
A heating resistor and a switch are connected in series across the generator's output terminals. When the switch is closed, a current flows through the circuit. To keep the coil rotating at the same constant speed, the student must exert a significantly larger turning force on the handle.
Explain why a larger turning force is needed when the switch is closed.
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.