Physics (school) · Part 07
Mains electricity and magnetism
Static charge, safe mains wiring, magnets and how motors and generators work.
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- Static electricityCharge that builds up on an insulator when electrons are rubbed from one material to another. Like charges repel and unlike charges attract.
- Mains electricityIn the UK, mains electricity is alternating current (a.c.) at 230 V and 50 Hz. The current keeps reversing direction. A battery gives direct current (d.c.), which flows one way.
- Plug wires and fusesA UK three-pin plug has a live wire (brown, carries the current), a neutral wire (blue, completes the circuit) and an earth wire (green and yellow, safety). A fuse melts if the current is too high.
- Earth wireA safety wire that connects a metal case to the ground. If the live wire touches the case, a large current flows down the earth wire, blows the fuse and cuts the power.
- Magnetic fieldsThe region around a magnet where another magnet or a magnetic material feels a force. Field lines run from north to south and are closest where the field is strongest.
- ElectromagnetA coil of wire with a current flowing makes a magnetic field like a bar magnet. Adding an iron core, more turns, or a bigger current makes it stronger. It switches off when the current stops.
- Motor effectA wire carrying current in a magnetic field feels a force. Reversing the current or the field reverses the force. A coil between two magnets will spin, which is how an electric motor works.
- Electromagnetic inductionA voltage is induced in a wire when it moves through a magnetic field, or when the field around it changes. This is how generators make electricity.