Alternating current :

direct current - current which only flows in one direction

Alternating current - current which repeatedly reverses its directions, flows one way than the other. Its frequency is the number of cycles it passes through each second.

uk mains frequency is 50 cycles per second / 50hz

Step up transformer :
Is used to transfer energy from power station to national grid. These transformers are used to make the alternating potential difference much bigger typically from about 25,000 to 132,000

Step down transformer :

Used to supply electricity from the national grid to the consumers in homes and offices. They are supplied electricity which has the same power as 230V Direct current supply.

Factories are supplied with a much larger p.d : from 100kv to 30Kv

By making the potential different large, much less current is needed to transfer the same amount of power so the power loss due to the resistance heating in the cables is much reduced.

This means that the national grid is an efficient way to transfer power

Plugs and cables:

Some appliances have earth wires, such as heaters. When you plug a heater in the plug case may sometimes be metal. The earth wire within th plug is there to stop the plug from becoming live if the live wire was to break and touch the case.

Plastic materials are good insulators as they are double insulated, therefore they require no earth wire connection. All appliances sold in the uk with a plastic case must be double insulated.

Earth wire - connected to the ground at 0v and only carries current if there is a fault. The longest pin of a 3 pin plug is designed to make contacted with the earth wire if the socket so when you plug an appliance in it is automatically earthed. The metal pins of a plug is made out of brass as brass is a good conductor and does not oxidise or rust. Plug is shapes to that wires and cables cannot touch each other when sealed.

to be finished

	Criado por Rayyan Abhram quase 9 anos atrás

Notes for all topics which may come up in GCSE