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P6F The dynamo effect Electricity can be generated by moving a wire near a magnet, or by moving a magnet near a wire. This is called the dynamo effect. A voltage is induced (made to happen) across a wire when the wire moves relative to a magnetic field. If the wire is moved in the opposite direction, the voltage is reversed. A voltage is also induced across a coil when the magnetic field in it changes. If the magnet is moved in the opposite direction, the voltage is reversed. Just Imagine the arrow moving to positive everytime it goes it and out. If the wire or coil is part of a complete circuit, a current will flow. Changing the size of the induced voltage The size of the induced voltage depends on the rate that the magnetic field changes. The faster it changes, the greater the induced voltage. The AC generator The AC (alternating current) generator makes use of the dynamo effect to produce electricity. One simple example is the bicycle dynamo. It has a wheel that touches the back tyre. As the bicycle moves, the wheel turns a magnet inside a coil. This induces enough electricity to run the bicycle’s lights. The faster the bicycle moves, the greater the induced current and the brighter the lights. A generator can be described as an electric motor working in reverse – instead of using electrical energy to produce kinetic energy, kinetic energy is used to produce electrical energy. You should be able to label a diagram of an AC generator. These are the main features you should identify: coil magnets slip rings brushes (alternating current) electricity produced Mains electricity is supplied at 50 Hz (50 complete waves per second) in the UK. How an AC generator works The slip rings are connected to the coil. The brushes are connected to the external circuit. The brushes touch the spinning slip rings, which maintain electrical contact between the coil and the external circuit. At the power station Electricity is a useful form of energy. It allows energy to be transmitted over long distances easily through cables, and it allows energy to be stored for use later on. The large generators used in power stations use electromagnets instead of permanent magnets. Electricity is generated when the electromagnet rotates inside coils of wire. The more turns there are on the coils of the electromagnet, the greater the size of the voltage generated. The speed at which the electromagnet is rotated is important. The faster the electromagnet is rotated: the greater the size of the voltage generated the higher the frequency of the AC As the electromagnet turns, the direction of the induced voltage and current changes every half-turn. This is why AC electricity is produced.