A U-shaped permanent magnet rests on a top-pan balance. A horizontal wire is clamped so that it passes between the poles of the magnet. The wire does not touch the magnet.
When there is a current in the wire, the force on the wire is upwards.
What happens to the reading on the balance?
It increases, because the wire exerts an equal downward force on the magnet
It decreases, because the magnet is pulled upwards towards the wire
It stays the same, because the force acts on the wire and not on the magnet
It decreases, because the upward force on the wire reduces the total weight
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.