Glossary — Magnetism and electromagnetism

Alternator — a generator that produces alternating current. A coil rotates in a magnetic field, and the induced current reverses every half turn.

Commutator — the part of a dynamo or a motor that reverses the connections every half turn. In a dynamo it keeps the output current in one direction. In a motor it keeps the coil turning.

Dynamo — a generator that produces direct current. A commutator reverses the connections every half turn, so the current in the outside circuit always flows the same way.

Electromagnet — a solenoid with an iron core. The iron core makes the field stronger, and the magnet can be switched on and off with the current.

Fleming's left-hand rule — a rule that gives the relative directions of the force, the current and the magnetic field for the motor effect. The first finger points along the field, the second finger along the current, and the thumb along the force.

Generator effect — the production of a potential difference across a conductor when the conductor moves relative to a magnetic field, or when the magnetic field around it changes. If the conductor is in a complete circuit, the effect drives a current.

Induced magnet — a material that becomes a magnet when it is placed in a magnetic field, and loses most or all of its magnetism when it is removed. Induced magnetism always causes a force of attraction.

Induced potential difference — the potential difference produced across a conductor by the generator effect.

Iron core — a piece of iron placed inside a solenoid to make the magnetic field much stronger. The field of the coil magnetises the iron.

Magnetic field — the region around a magnet or a current-carrying conductor where a force acts on a magnetic material or on another magnet.

Magnetic flux density — the strength of a magnetic field, measured in tesla (T). Its symbol is $B$.

Magnetic material — a material that is attracted by a magnet. Iron, steel, cobalt and nickel are magnetic materials.

Motor effect — the force that acts on a current-carrying conductor when it is placed in a magnetic field.

National grid — the network of cables and transformers that carries electrical energy around the country. It transmits at high potential difference to keep the current, and the energy wasted as heat, small.

Permanent magnet — a magnet that produces its own magnetic field all the time.

Plotting compass — a small compass with a needle that can turn freely. It is used to find the direction of a magnetic field at a point.

Pole — one of the two places on a magnet where the magnetic force is strongest. Two like poles repel, and two unlike poles attract.

Solenoid — a coil of wire wound into a cylinder. The field inside is strong and uniform, and outside it the field has the shape of the field of a bar magnet.

Step-down transformer — a transformer with fewer turns on the secondary coil than on the primary coil, so the secondary potential difference is smaller.

Step-up transformer — a transformer with more turns on the secondary coil than on the primary coil, so the secondary potential difference is larger.

Transformer — a device that changes the size of an alternating potential difference. Two coils are wound on an iron core, and the ratio of the potential differences equals the ratio of the numbers of turns.

Turns — the number of times the wire is wound around the coil of a solenoid or a transformer.