Mains Electricity

Question 1

What does AC mean?

Answer 1

Alternating Current.

This is current which is constantly
changing between a negative and a
positive maximum.

Question 2

What does DC mean?

Answer 2

Direct Current.

This is current which takes a constant
value.

Question 3

Is mains electricity an AC supply or a DC supply?

What do each of these stand for?

Answer 3

Mains electricity is an AC supply

Question 4

What is meant by the frequency of a supply?

Answer 4

This is the rate at which an AC current

changes

Question 5

What is the frequency and voltage of the UK mains

electricity supply?

Answer 5

● Frequency: 50 Hz

● Voltage: 230V

Question 6

What type of current do batteries and cells supply?

Answer 6

Direct current

Question 7

What is the power rating of an appliance?

Answer 7

It shows how much energy a device

converts per second

Question 8

What wires does a typical appliance have?

Answer 8

1. Live wire
2. Neutral wire
3. Earth wire

Question 9

What colour is the live wire?

Answer 9

Brown

Question 10

What colour is the neutral wire?

Answer 10

Blue

Question 11

What colour is the earth wire?

Answer 11

Green and yellow (striped)

Question 12

Explain when the Earth wire does and doesn’t carry

a current

Answer 12

● Under normal circumstances, no current
flows through the Earth wire
● Current flows when a fault occurs in the
appliance (such as a surge or the casing
becoming live)

Question 13

What potential is the neutral wire at?

Answer 13

0 volts

Question 14

State the potential difference between the live and

earth wires

Answer 14

230 Volts

Question 15

What is the purpose of the neutral wire?

Answer 15

To complete the circuit by connecting the

appliance back to the mains supply.

Question 16

For metal appliances, where is the Earth wire

connected to? Why?

Answer 16

● Earth wire is connected to the metal casing
of the appliance
● If live wire becomes touches the casing, the
current will flow through the Earth wire,
preventing electrocution

Question 17

How does a fuse wire stop the device from getting

damaged?

Answer 17

When the current becomes too high the fuse wire
will melt and break, therefore stopping current
from flowing to the appliance and preventing
damage.

Question 18

Why is it important to connect a fuse or switch to the

live wire?

Answer 18

When the switch is turned off, or when the fuse
breaks, it will break the circuit and stop current
running through the wire. This provides a method
to stop current flowing into the appliance.

Question 19

Why is it dangerous to have a connection between

the earth wires and the live wire?

Answer 19

In can result in a current surge, causing

electrical shocks.