A classroom public-address system uses a moving-coil loudspeaker. A cone is attached to a coil that sits in the magnetic field of a permanent magnet. A varying current flows through the coil. Which statement explains how the loudspeaker produces sound?
The varying current magnetises the cone, so the permanent magnet pulls the cone to and fro.
The motor effect gives a changing force on the coil, so the cone vibrates and pushes the air.
The varying current changes the strength of the permanent magnet, so the magnet vibrates the air.
The varying current flows into the cone and then travels through the air as sound waves.
90 exam-style questions on AQA GCSE Physics 7.2 The motor effect, covering 7.2.1 Electromagnetism, 7.2.2 Fleming's left-hand rule (HT only), 7.2.3 Electric motors (HT only), and 7.2.4 Loudspeakers (HT only). Each one has a worked solution and a mark scheme showing where the marks go.