A transformer only works when there is an alternating current in its primary coil.
Which statement explains why?
A direct current would flow straight through the iron core into the secondary coil
A direct current would magnetise the core permanently, so the core stops working
Only a changing magnetic field in the core can induce a p.d. in the secondary coil
An alternating current carries more energy, so it can cross the gap between coils
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.