P5 Electricity in the home

Question 1

what is direct current?

Answer 1

current that flows in only one direction

Question 2

what is alternating current?

Answer 2

current that repeatedly reverses its direction of flow

Question 3

what type of current does the main electricity supply use?

Answer 3

alternating current

Question 4

what is the frequency of the mains electricity?

Answer 4

50Hz

Question 5

which two wires are in a mains circuit?

Answer 5

a live wire and a neutral wire

Question 6

what colour is the live wire?

Answer 6

brown

Question 7

what colour is the neutral wire?

Answer 7

blue

Question 8

what are step-up transformers?

Answer 8

• used at power stations to transfer electricity to the National Grid
• used to increase the size of the alternating potential difference and decrease the current

Question 9

what are step-down transformers?

Answer 9

• used to supply electricity from the National Grid to consumers
• used to decrease the size of the alternating potential difference and increase the current

Question 10

what is the advantage of making the grid potential difference very large?

Answer 10

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

Question 11

what are the three wires in a three-core cable?

Answer 11

live wire, neutral wire and earth wire

Question 12

what colour is the earth wire?

Answer 12

green and yellow stripes

Question 13

what is the function of the earth wire?

Answer 13

• a safety wire to stop the appliance becoming live
• carries a current only if there is a fault

Question 14

what is the function of the live wire?

Answer 14

carries the alternating current from the supply in a mains power supply, 230V

Question 15

what is the function of the neutral wire?

Answer 15

completes the circuit in a mains power supply

Question 16

what is the potential difference of a mains power supply?

Answer 16

230V

Question 17

If the electrician touches the live wire he will receive an electric shock. Explain why.

Answer 17

• the potential of the live wire is 230V
• the potential of the electrician is 0V
• so there is a large potential difference between the live wire and the electrician
• charge/current passes through his body

Question 18

what is the function of a fuse?

Answer 18

if too much current passes through the wire in the fuse, it melts and cuts the live wire off

Question 19

why is copper used for the wires?

Answer 19

it is a good electrical conductor and bends easily

Question 20

why is plastic used in a plug?

Answer 20

it is a good electrical insulator, so if anyone touches the cable, it stops them from getting an electric shock

Question 21

what is the National Grid?

Answer 21

a system of cables and transformers linking power stations to consumers