In an alternator, a coil rotates in a magnetic field. At certain instants, the induced potential difference is zero.
Why is the induced potential difference zero at these instants?
The coil stops for an instant at the top of each turn, so it is not moving at all
The sides of the coil are moving parallel to the field, so no field lines are cut
The magnetic field of the magnet reverses at that instant, so the field is zero
The current in the coil is at its largest, so it cancels the induced p.d. exactly
48 exam-style questions on OCR GCSE Physics 4.2 Uses of magnetism, covering 4.2.1 The motor effect, 4.2.2 Fleming's left-hand rule, 4.2.3 The force on a current-carrying conductor, 4.2.4 The electric motor, 4.2.5 Electromagnetic induction, 4.2.6 Alternators and dynamos, 4.2.7 How transformers work, 4.2.8 Transformer turns ratio, 4.2.9 Potential differences and turns in transformers, and 4.2.10 Microphones, loudspeakers and headphones. Each one has a worked solution and a mark scheme showing where the marks go.