Mains electricity Flashcards
State the two types of voltage
Types of voltage
Direct voltage
Alternating voltage
What is a direct voltage
A direct voltage maintains a constant value and does not change direction
Where do we receive direct voltage from
A direct voltage which we receive from batteries and power supplies
What type of voltage is mains electricity
Mains electricity is an alternating voltage
What is alternating voltage
Alternating voltage is voltage that repeatedly changes it’s value and reverses it’s direction
Sketch the graph for direct voltage
Time - x axis
Voltage in volts y axis
1st quadrant graph
Straight line
Sketch the graph for alternating voltage
See book
https://bam.files.bbci.co.uk/bam/live/content/z3m3kqt/small
time - x axis
voltage in volts - y axis
How long does one complete cycle take for alternating voltage
Once complete cycle takes 0.02 seconds
What is the frequency of alternating voltage
Frequency of alternating voltage = 50Hz - 50 complete cycles every second
What is the voltage of alternating voltage
Voltage of alternating voltage = 230 v
Through which mechanism are most electrical appliances connected to the mains through
Most electrical appliances are connected to the mains using three-core cable.
What is inside the electrical cable
The electrical cable contains three wires
What are the wires inside the electrical cable covered in
Each wire is covered with insulation
Why is the insulation covering each wire colour coded
The insulation covering each wire is colour coded for easy
identification
State the names of the three wires in a cable
The wires are called
Live
Neutral
Earth
What is the colour of the insulation covering the live wire
Brown
What is the colour of the insulation covering the neutral wire
Blue
What is the colour of the insulation covering the earth wire
Green and Yellow
State the function of the live wire
The live wire provides the alternating potential difference from the mains supply
State the function of the earth wire
The earth wire is a safety wire to stop the appliance from becoming live
State the function of the neutral wire
The neutral wire completes the circuit
What is the voltage of:
The live wire
The earth wire
The neutral wire
Live wire - 230 V
Earth wire - 0V
Neutral wire - 0V
When does the earth wire carry current
The earth wire carries a current only if there is a fault
What is the purpose of the longest pin of a three- pin plug
How is this useful
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
State what the pins are made out of and why - why aren’t they made out of copper
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
What is the cable and the wire made out of and why
The cable and the wires are made out of plastic because plastic is a good insulator
Why is the inside of the case shaped
The inside of the case is shaped so that the wires and the pins can’t touch each other when the plug is sealed
Which wire is connected to the live pin/terminal
The live wire is connected to the live pin
Which wire is the fuse connected to
The fuse is connected to the live wire
Which wire is connected to the neutral pin/terminal
The neutral wire
Which wire is connected to the earth pin/terminal
The earth wire
Which wire does a two-core cable not have
A two-core cable does not have an earth wire
What are the wires made out of and why
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.
Why is each wire encased in plastic
Each wire is encased in plastic to stop the wires touching and causing a short circuit
Draw a diagram of the structure of a cable
https://bam.files.bbci.co.uk/bam/live/content/zbxb87h/small
What is the cable grip made out of
Plastic
State the function of the cable grip
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.
What types of appliances need an earth wire
Appliances with a metal case need an earth wire
Explain how a fuse protets the wiring of a circuit
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
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
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
What effect does a current through a wire have on the wire
The current heats up the wire
Which two parts of a plug protect the wiring of a circuit
Fuse and Earth wire
Define double insulated
It means that there are two layers of insulating material
Define direct current
The current is always in the same direction
State why a kettle with the highest power will boil water in the shortest amount of time
A greater energy will be passed from the kettle into the water per second
What can happen if the fuse for an appliance is lower than the one recoomended
The wire in the fuse could melt immediately, breaking the circuit and stopping the flow of electricity
What can happen if the fuse which is used is higher than the one recommended
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
What do double insulated appliances have -
why is this good
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
Draw the symbol for double insulated
https://bam.files.bbci.co.uk/bam/live/content/zchcjxs/small
If an appliance is double insulated, what wire does it not need to have
Appliances that are double insulated do not need an earth wire
Calculate the value of a fuse
A laptop charger is 65W
Calculate the size of fuse needed
And explain your answer
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)
What does the amount of energy transfer in an appliance depend on
The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance.
What happens, when charge flows through a circuit
Work is done when charge flows in a circuit
State the standard fuse sizes
3A
5A
7A
13A
How does the Residual Current Circuit Breaker Work
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.
