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Electricity - Mains Electricity - Coggle Diagram
Electricity - Mains Electricity
Current
Direct current - A direct current flows in one direction only. Appears as a straight horizontal line at a constant voltage on a graph. Examples: car batteries, dry cells and solar cells.
Alternating current - An alternating current regularly changes direction. Appears as a curve alternating between positive and negative voltages. Examples: mains electrical supply, generated at a frequency of 50 Hz and is delivered to houses at 230 V.
Household electricity
Plugs - A plug connects a device to the mains electricity supply. The cable between the device and the three-pin plug contains three copper wires that are coated with plastic.
Outer insulation - All three cables are bundled together and there is extra plastic insulation wrapped around them for safety.
Cable grip - This holds the cable tightly in place so that wires don't become loose.
Live wire - Copper wire coated with brown plastic along which the current enters the device.
Fuse - A glass or ceramic canister containing a thin wire that melts if the current gets too high.
Neutral wire - Copper wire coated in blue plastic that also connects to the cable in the wall and completes the circuit.
Earth wire - Copper wire coated in striped plastic that provides a path for current to flow from the case of the device to the ground if there's a fault.
Earthing - Without the earth wire, if a fault occurs and the live wire becomes loose, there is a danger that it will touch the case. The next person who uses the appliance could get electrocuted.
Fuses - A fuse provides a built-in fail-safe to the electrical circuit for a device. The fuse contains a thin wire that will melt if the current gets too high.
Electrical appliances
All electrical appliances transfer energy from one store to another, for example chemical energy in the fuel in power stations. This is transferred into kinetic energy in a fan or heat energy in a cooker.
The amount of energy transferred depends on the power (the energy transferred each second) and the amount of time the appliance is switched on for.
energy = power x time, E = P x t
Alternating current and The National Grid
The National Grid distributes electricity across the country. The National Grid connects power stations to homes, workplaces and public buildings all around the country. The electricity may be produced by a conventional power station turning a generator or by another method.
Transformers - Used to change voltages and currents in transmission lines. Formed from two coils of wire around a magnetic core. Number of coils determines whether it will step-up or step-down the voltage. A step-up transformer is used to increase the voltage and reduce the current. A step-down transformer, reduces the voltage from the transmission voltage to the safer voltage of 230 V for home use.
Transmission lines - As an electric current flows through the thick cables held up by the pylons, they will get hotter and dissipate energy to the surroundings.
power = current squared x resistance, P = I squared x R
To ensure that the minimum amount of power is lost from the cables, the cables are thick so that their resistance is low.
