Chapter 7 - Mains Electricity

Question 1

A hairdryer is connected to the mains supply takes a current of 5.5A What fuse should be used? a) 5A b) 7A c) 13A

Answer 1

b) 7A Because it is the nearest above

Question 2

A hair dryer has a plastic case so there is no need for an earth wire connection to the plug. Explain why the hairdryer is still safe to use. (2)

Answer 2

• Plastic insulator, so doesn’t conduct
• No risk of shock or electrocution

Question 3

What is direct current? [1 mark]

Answer 3

Current in a single direction

Question 4

What colours are the following wires: {3 marks}

• Neutral
• Live
• Earth

Answer 4

Neutral - Blue

Live - Brown

Earth - Green/Yellow

Question 5

What voltage is the UK mains supply? {1 mark}

Answer 5

230V

Question 6

Name 2 safety precautions when using plugs, and the risks that come with them {4 marks}

Answer 6

• Check cables aren’t frayed (live parts might be uncovered)
• Check there’s no water near electrical objects (water is a good insulator)

Question 7

Name 2 advantages of using RCCB’s over fuses {2 marks}

Answer 7

• RCCB’s can be easily reset, so they don’t have to be replaced
• RCCB’s respond faster

Question 8

State the equation linking power, current and voltage {1 mark}

Answer 8

Power = Current x Voltage

Question 9

Give two reasons why lamps are wired in parallel {2 marks}

Answer 9

• So that the lamps work independently
• So that they all get the same voltage (230V)

Question 10

Explain how a fuse protects a circuit {4 marks}

Answer 10

• Current increases over max value of fuse
• Fuse wire melts
• Cuts off current
• Prevents wires in circuit from overheating

Question 11

Two heating elements can be connected in series or in parallel. Describe an advantage of each method {2 marks}

Answer 11

Series -

Parallel -