Electricity in the Home

CBE

Wiring a plugWiring a plug

DC and ACDC and AC

DC stands for “Direct Current” – the current only flows in one direction:

AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)

1/50th s

240V

V

V

Time

T

FusesFuses

Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____.

Words – large, harm, safety, melt, live, circuit, fuse

Circuit breakersCircuit breakers

If the current becomes too high the __________ is activated. This will ______ the iron and the contact will be _______. This will break the circuit.

Circuit breakers have two main advantages over fuses: they work ______ and can easily be ______.

Words – electromagnet, broken, attract, reset, quicker

Earth wiresEarth wires

Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows.

Words – fuse, fault, metal, surges, touch

The National GridThe National GridElectricity reaches our homes from power stations through the National Grid:

If electricity companies transmitted electricity at 240 volts through overhead power lines there would be too much ______ loss by the time electricity reaches our homes. This is because the current is ___. To overcome this they use devices called transformers to “step up” the voltage onto the power lines. They then “____ ____” the voltage at the end of the power lines before it reaches our homes. This way the voltage is _____ and the current and power loss are both ____.

Power stationStep up

transformerStep down

transformerHomes

Words – step down, high, power, low, high

TransformersTransformersTransformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil.

Voltage across primary (Vp)

No. of turns on secondary (Ns)

Voltage across secondary (Vs)

No. of turns on primary (Np)

Words – alternating, magnetic field, induce, step up, voltage

We can work out how much a transformer will step up or step down a voltage: