Supplying Electricity

Question 1

What type of current does a cell or battery provide?

Answer 1

A direct current (dc)

Question 2

Which way does a direct current flow and what is it produced by?

Answer 2

• Only flows in one direction
• Produced by a direct potential difference

Question 3

What type of current does mains electricity supply?

Answer 3

An alternating current (ac)

Question 4

Which way does an alternating current flow and what is it produced by?

Answer 4

• Repeatedly reverses directions
• Produced by an alternating potential difference

Question 5

What happens to the positive and negative terminals of an alternating power supply?

Answer 5

They swap over with a regular frequency

Question 6

What is the frequency of the UK mains electricity supply?

Answer 6

50Hz

Question 7

What is the voltage of the UK mains electricity supply?

Answer 7

230V

Question 8

What is the Earth wire?

Answer 8

• A safety wire to stop the appliance becoming live
• Potential difference is 0V
• It only carries a current if there is a fault
• Green and yellow

Question 9

What is the neutral wire?

Answer 9

• Completes the circuit
• Potential difference is 0V
• Blue

Question 10

What is the live wire?

Answer 10

• Dangerous because it has a high potential difference of 230V
• Brown
• Cause a large current to flow through you if touched

Question 11

What metal is used for most wires in the UK and why?

Answer 11

• Copper
• Good electrical conductor
• Bends easily

Question 12

What is used for the wire coating and why?

Answer 12

• Plastic
• Good electrical insulator

Question 13

What is a short circuit?

Answer 13

A very large current flowing if the live wire touches the neutral wire

Question 14

What happens when something short circuits?

Answer 14

The fuse melts and disconnects the live wire from the mains, keeping the appliance safe

Question 15

What is the national grid?

Answer 15

A nationwide network of cables and transformers that link power stations to homes, offices, and other consumers of mains electricity

Question 16

What are transformers?

Answer 16

Devices that can change the potential difference of an alternating current

Question 17

How much potential difference of electricity do power stations generate?

Answer 17

An alternating potential difference of about 25,000V

Question 18

What are step-up transformers used for?

Answer 18

To increase the potential difference from the power station to the transmission cables

Question 19

What do the cables in the National Grid transfer?

Answer 19

Electrical power at a potential difference of up to 400,000V

Question 20

What do step-down transformers do?

Answer 20

To decrease the potential difference from the transmission cables to the mains supply in homes and offices so that it is safe to use

Question 21

What does a high potential difference across the transmission cables mean?

Answer 21

A lower current is needed to transfer the same amount of power

Question 22

What does a lower current in the cables mean?

Answer 22

• Less electrical power is wasted due to heating of the cables
• This makes the National Grid an efficient way to transfer energy

Question 23

What happens when you turn an electrical appliance on?

Answer 23

The potential difference of the mains supply causes charge (carried by electrons) to flow through it