P2 - Household Electricity

Question 1

What is direct current?

Answer 1

Where the current flows in one direction only for example in batteries.

Question 2

What is alternating current?

Answer 2

Where the current changes direction for example mains electricity.

Question 3

What are the properties of mains electricity?

Answer 3

Potential difference is 230V.

Frequency is 50Hz.

Question 4

This is an oscilloscope reading. What does it show?

Answer 4

Direct Current

Question 5

This is an oscilloscope reading. What does it show?

Answer 5

Alternating Current

Question 6

What happens if we use a diode on an AC oscilloscope?

Answer 6

Trace on only one half.

Question 7

What colour is neutral wire?

Answer 7

Blue.

Question 8

What colour is live wire?

Answer 8

Brown.

Question 9

What colour is earth wire?

Answer 9

Green and yellow.

Question 10

Describe an electrical wire.

Answer 10

3 copper wires inside - live, neutral and earth. (Earth not needed if the object is double insulated. Surrounded by a plastic insulator.

Question 11

What is the live wire for?

Answer 11

Carrying electrical supply.

Question 12

What is the neutral wire for?

Answer 12

Carrying electrical supply.

Question 13

What is the earth wire for?

Answer 13

Safety, particularly for devices which have a metal case in conjunction with the fuse.

Question 14

Describe how a fuse works.

Answer 14

Fuses have different current ratings (3A, 5A, 13A). If the current is higher than this rating then the fuse wire will melt.

Question 15

Where should fuses always be placed?

Answer 15

Fuses should always be placed in series with the live wire and the appliance so if the fuse melts then the appliance is cut off from the live.

Question 16

What is the danger of using a fuse with an incorrect current rating?

Answer 16

If a fuse with a too high current rating is used then the fuse will not melt when it should.
If a fuse with a too low current rating is used then the fuse will melt even at safe levels for the appliance.

Question 17

What does a fuse protect against?

Answer 17

It protects the appliance and prevents fires.

Question 18

What are circuit breakers?

Answer 18

Circuit breakers are electromagnetic switches which open (trip) when there is a fault which prevents the current in the live wire from flowing.

Question 19

Where should fuses always be placed?.

Answer 19

Fuses should be placed in series with the live wire so if the current is too large then the magnetic field will be strong enough to pull the switch contacts open. This stops the current.

Question 20

What is an advantage of a circuit breaker over a fuse?

Answer 20

1) They work faster.

2) They can be reset.

Question 21

What does RCCB stand for?

Answer 21

Residual Current Circuit Breaker

Question 22

How does an RCCB work?

Answer 22

It detects a difference in current between the live and neutral wire. They are A LOT faster than regular circuit breakers or fuses.

Question 23

What does earthing protect against?

Answer 23

Electric Shocks. If there was a fault and the live wire came into contact with the metal casing of the appliance and you touched it then the current would go through you to get to ground. Earthing would prevent this.

Question 24

How does earthing protect you?

Answer 24

If there was a fault and the live wire touched the metal case

The current travels through the metal casing to the earth wire

The earth wire has a low resistance which would cause the current to increase

This would melt the fuse or trigger the circuit breaker and prevent electrocution.

Question 25

What is double insulation?

Answer 25

Where the case of an appliance is made of an insulator so there is no need for an earth wire.