1. Electricity in the Home CBE

2. Wiring a plug

3. DC 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) 1/50 th s 240V V V Time T

4. Fuses 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

5. Circuit 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

6. Earth 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

7. The National Grid Electricity 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 station Step up transformer Step down transformer Homes Words – step down, high, power, low, high

8. Transformers Transformers 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 (V p ) No. of turns on secondary (N s )Voltage across secondary (V s ) No. of turns on primary (N p ) Words – alternating, magnetic field, induce, step up, voltage We can work out how much a transformer will step up or step down a voltage: