Why does placing an iron core inside a solenoid make its magnetic field much stronger?
The iron lowers the resistance of the coil, so the current increases
The iron becomes an induced magnet and its field adds to that of the coil
The iron is a permanent magnet, so it adds its own field to that of the coil
The iron carries part of the current through the middle of the coil
44 exam-style questions on OCR GCSE Physics 4.1 Magnets and magnetic fields, covering 4.1.1 Magnetic poles, attraction and repulsion, 4.1.2 Permanent and induced magnets, 4.1.3 The magnetic field of a magnet, 4.1.4 Compasses and the Earth's magnetic field, 4.1.5 The magnetic field around a current-carrying wire, 4.1.6 Field strength, current and distance, and 4.1.7 Solenoids and electromagnets. Each one has a worked solution and a mark scheme showing where the marks go.