Emergency electricity generators are used in major buildings in case the mains electricity should fail. This is very important in buildings like hospitals for instance.

A generator is composed of coils of wire that rotate within a magnetic field. When the wire cuts across magnetic field lines it induces a potential difference (voltage). In a complete circuit the creation of a potential difference leads to an electric current which is able to travel through the circuit.

If an piece of insulated wire is connected to an ammeter then moved between the poles of a U-shaped magnet a current is produced each time the magnetic field line is cut by the wire. This is called the dynamo effect. If the wire was to be made into a coil then the current would increase.

Forcing a rectangular coil to rotate within a magnetic field it’s possible to make a simple alternating current (AC) generator.

• – An ammeter and coil are connected by two metal brushes.
• – The metal brushes are attached to the commutator.

As long as the coil turns in one direction, the ammeter points one way then the other. The current being produced is alternating current (AC).

As the rotation of the coil increases:

• – the alternating current’s peak value increases
• – the frequency of the alternating current increases

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Basic Magnetism

A region where a magnetic force is being exerted is known as a magnetic field. Magnetic field lines always run from north to south.

• – Poles which are opposite attract each other.
• – Poles which are like repel each other.
• – The neutral point is the area in which there’s no magnetic force.

Imagine a wire between two opposite magnets. The magnetic field lines would run from north to south. However, not all the wire’s field lines correspond with with the magnetic field lines of the magnets. In other words, part of the wire’s field is going in the opposite direction of the poles’ field lines.

Due to this, the wire is pushed up by the magnetic force in order to cancel out the forces which are moving in the opposite direction to the magnetic field lines. This is called the catapult effect.