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GCSE Physics LTS > Mains electricity > Flashcards

Mains electricity Flashcards

1
Q

State the two types of voltage

A

Types of voltage
Direct voltage
Alternating voltage

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2
Q

What is a direct voltage

A

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

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3
Q

Where do we receive direct voltage from

A

A direct voltage which we receive from batteries and power supplies

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4
Q

What type of voltage is mains electricity

A

Mains electricity is an alternating voltage

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5
Q

What is alternating voltage

A

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

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6
Q

Sketch the graph for direct voltage

A

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

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7
Q

Sketch the graph for alternating voltage

A

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

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8
Q

How long does one complete cycle take for alternating voltage

A

Once complete cycle takes 0.02 seconds

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9
Q

What is the frequency of alternating voltage

A

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

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10
Q

What is the voltage of alternating voltage

A

Voltage of alternating voltage = 230 v

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11
Q

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

A

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

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12
Q

What is inside the electrical cable

A

The electrical cable contains three wires

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13
Q

What are the wires inside the electrical cable covered in

A

Each wire is covered with insulation

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14
Q

Why is the insulation covering each wire colour coded

A

The insulation covering each wire is colour coded for easy
identification

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15
Q

State the names of the three wires in a cable

A

The wires are called
Live
Neutral
Earth

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16
Q

What is the colour of the insulation covering the live wire

A

Brown

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17
Q

What is the colour of the insulation covering the neutral wire

A

Blue

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18
Q

What is the colour of the insulation covering the earth wire

A

Green and Yellow

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19
Q

State the function of the live wire

A

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

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20
Q

State the function of the earth wire

A

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

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21
Q

State the function of the neutral wire

A

The neutral wire completes the circuit

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22
Q

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

A

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

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23
Q

When does the earth wire carry current

A

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

24
Q

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

A

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

25
Q

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

A

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

26
Q

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

A

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

27
Q

Why is the inside of the case shaped

A

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

28
Q

Which wire is connected to the live pin/terminal

A

The live wire is connected to the live pin

29
Q

Which wire is the fuse connected to

A

The fuse is connected to the live wire

30
Q

Which wire is connected to the neutral pin/terminal

A

The neutral wire

31
Q

Which wire is connected to the earth pin/terminal

A

The earth wire

32
Q

Which wire does a two-core cable not have

A

A two-core cable does not have an earth wire

33
Q

What are the wires made out of and why

A

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.

34
Q

Why is each wire encased in plastic

A

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

35
Q

Draw a diagram of the structure of a cable

A

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

36
Q

What is the cable grip made out of

A

Plastic

37
Q

State the function of the cable grip

A

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.

38
Q

What types of appliances need an earth wire

A

Appliances with a metal case need an earth wire

39
Q

Explain how a fuse protets the wiring of a circuit

A

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

40
Q

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

A

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

41
Q

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

A

The current heats up the wire

42
Q

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

A

Fuse and Earth wire

43
Q

Define double insulated

A

It means that there are two layers of insulating material

44
Q

Define direct current

A

The current is always in the same direction

45
Q

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

A

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

46
Q

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

A

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

47
Q

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

A

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

48
Q

What do double insulated appliances have -
why is this good

A

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

49
Q

Draw the symbol for double insulated

A

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

50
Q

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

A

Appliances that are double insulated do not need an earth wire

51
Q

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

A

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)

52
Q

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

A

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

53
Q

What happens, when charge flows through a circuit

A

Work is done when charge flows in a circuit

54
Q

State the standard fuse sizes

A

3A
5A
7A
13A

55
Q

How does the Residual Current Circuit Breaker Work

A

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.

GCSE Physics LTS (30 decks)

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