Mains electricity

Question 1

State the two types of voltage

Answer 1

Types of voltage
Direct voltage
Alternating voltage

Question 2

What is a direct voltage

Answer 2

A direct voltage maintains a constant value and does not change direction

Question 3

Where do we receive direct voltage from

Answer 3

A direct voltage which we receive from batteries and power supplies

Question 4

What type of voltage is mains electricity

Answer 4

Mains electricity is an alternating voltage

Question 5

What is alternating voltage

Answer 5

Alternating voltage is voltage that repeatedly changes it’s value and reverses it’s direction

Question 6

Sketch the graph for direct voltage

Answer 6

Time - x axis
Voltage in volts y axis
1st quadrant graph
Straight line

Question 7

Sketch the graph for alternating voltage

Answer 7

See book
https://bam.files.bbci.co.uk/bam/live/content/z3m3kqt/small
time - x axis
voltage in volts - y axis

Question 8

How long does one complete cycle take for alternating voltage

Answer 8

Once complete cycle takes 0.02 seconds

Question 9

What is the frequency of alternating voltage

Answer 9

Frequency of alternating voltage = 50Hz - 50 complete cycles every second

Question 10

What is the voltage of alternating voltage

Answer 10

Voltage of alternating voltage = 230 v

Question 11

Through which mechanism are most electrical appliances connected to the mains through

Answer 11

Most electrical appliances are connected to the mains using three-core cable.

Question 12

What is inside the electrical cable

Answer 12

The electrical cable contains three wires

Question 13

What are the wires inside the electrical cable covered in

Answer 13

Each wire is covered with insulation

Question 14

Why is the insulation covering each wire colour coded

Answer 14

The insulation covering each wire is colour coded for easy
identification

Question 15

State the names of the three wires in a cable

Answer 15

The wires are called
Live
Neutral
Earth

Question 16

What is the colour of the insulation covering the live wire

Answer 16

Brown

Question 17

What is the colour of the insulation covering the neutral wire

Answer 17

Blue

Question 18

What is the colour of the insulation covering the earth wire

Answer 18

Green and Yellow

Question 19

State the function of the live wire

Answer 19

The live wire provides the alternating potential difference from the mains supply

Question 20

State the function of the earth wire

Answer 20

The earth wire is a safety wire to stop the appliance from becoming live

Question 21

State the function of the neutral wire

Answer 21

The neutral wire completes the circuit

Question 22

What is the voltage of:
The live wire
The earth wire
The neutral wire

Answer 22

Live wire - 230 V
Earth wire - 0V
Neutral wire - 0V

Question 23

When does the earth wire carry current

Answer 23

The earth wire carries a current only if there is a fault

Question 24

What is the purpose of the longest pin of a three- pin plug
How is this useful

Answer 24

The longest pin of a three-pin plug is designed to make contact with the earth wire of a wall socket circuit.
When you plug an appliance with a metal case into a wall, the case is automatically earthed

Question 25

State what the pins are made out of and why - why aren't they made out of copper

Answer 25

The pins are made of brass because brass is a good conductor of electricity, it is a hard metal and it does not rust or oxidise. Copper isn't as hard as brass even though it conducts electricity better

Question 26

What is the cable and the wire made out of and why

Answer 26

The cable and the wires are made out of plastic because plastic is a good insulator

Question 27

Why is the inside of the case shaped

Answer 27

The inside of the case is shaped so that the wires and the pins can't touch each other when the plug is sealed

Question 28

Which wire is connected to the live pin/terminal

Answer 28

The live wire is connected to the live pin

Question 29

Which wire is the fuse connected to

Answer 29

The fuse is connected to the live wire

Question 30

Which wire is connected to the neutral pin/terminal

Answer 30

The neutral wire

Question 31

Which wire is connected to the earth pin/terminal

Answer 31

The earth wire

Question 32

Which wire does a two-core cable not have

Answer 32

A two-core cable does not have an earth wire

Question 33

What are the wires made out of and why

Answer 33

The wires are made of copper because copper is a good conductor of electricity. Copper is also flexible, causing the cables to be flexible as well.

Question 34

Why is each wire encased in plastic

Answer 34

Each wire is encased in plastic to stop the wires touching and causing a short circuit

Question 35

Draw a diagram of the structure of a cable

Answer 35

https://bam.files.bbci.co.uk/bam/live/content/zbxb87h/small

Question 36

What is the cable grip made out of

Answer 36

Plastic

Question 37

State the function of the cable grip

Answer 37

This holds the cable tightly in place so that wires do not become loose. It also grips the outer insulation of the cables, so if there is any force on the cable, the whole cable is pulled instead of the individual wires.

Question 38

What types of appliances need an earth wire

Answer 38

Appliances with a metal case need an earth wire

Question 39

Explain how a fuse protets the wiring of a circuit

Answer 39

If the current through the fuse wire gets too high, this will cause it to heat up and melt, breaking the circuit and stoping the flow of electricity

Question 40

If a fault makes the metal case live, the earth wire and the fuse inside the plug prevent the mains cable from overheating and causing a fire Explain how

Answer 40

When the live wire makes contact with the metal case, the resistance between the live wire and the earth wire decreases. Therefore the current through the live wire will increase This causes the wire in the fuse to heat up and melt, breaking the circuit and stopping the flow of electricity

Question 41

What effect does a current through a wire have on the wire

Answer 41

The current heats up the wire

Question 42

Which two parts of a plug protect the wiring of a circuit

Answer 42

Fuse and Earth wire

Question 43

Define double insulated

Answer 43

It means that there are two layers of insulating material

Question 44

Define direct current

Answer 44

The current is always in the same direction

Question 45

State why a kettle with the highest power will boil water in the shortest amount of time

Answer 45

A greater energy will be passed from the kettle into the water per second

Question 46

What can happen if the fuse for an appliance is lower than the one recoomended

Answer 46

The wire in the fuse could melt immediately, breaking the circuit and stopping the flow of electricity

Question 47

What can happen if the fuse which is used is higher than the one recommended

Answer 47

If a fuse is used which is higher than the one recommended, the current will increase and the fuse wire will not melt fast enough

Question 48

What do double insulated appliances have - why is this good

Answer 48

Double insulated appliances have plastic cases, without any wires connected to it. This means that the case cannot become live, because plastic does not conduct electricity. If one layer is damaged, the appliance is still safe for the user

Question 49

Draw the symbol for double insulated

Answer 49

https://bam.files.bbci.co.uk/bam/live/content/zchcjxs/small

Question 50

If an appliance is double insulated, what wire does it not need to have

Answer 50

Appliances that are double insulated do not need an earth wire

Question 51

Calculate the value of a fuse A laptop charger is 65W Calculate the size of fuse needed And explain your answer

Answer 51

Power = 65W Voltage = 230v (from mains electricity) Current? P = I x V I = P/V = 65/230 = 0.28A Sizes 3A, 5A, 7A, 13A Choose 3A fuse - choose the fuse where the current is as low as possible but it has a higher current than the current from the appliance EXPLAIN - The size of the fuse (it's current) is as low as possible, but still greater than the current from the appliance (charger)

Question 52

What does the amount of energy transfer in an appliance depend on

Answer 52

The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.

Question 53

What happens, when charge flows through a circuit

Answer 53

Work is done when charge flows in a circuit

Question 54

State the standard fuse sizes

Answer 54

3A 5A 7A 13A

Question 55

How does the Residual Current Circuit Breaker Work

Answer 55

The RCCB detects the current in the wire and the neutral wire, if the current is different it automatically switches the circuit off. These work much faster than a normal fuse.