Mains Electricity Flashcards
What is the frequency mains electricity is generated at and voltage it’s delivered to houses in
50Hz
230V
How does a direct current look in a voltage time graphs
As a straight line
How does an alternating current look on a voltage time graph
As a wavey line
Alternating.between postitive and negative values
Why are the wires made out of copper?
Because they are good conductors
Why are the wires coated with plastic
Because it’s a good insulator
What is the outer insulation of a cable for?
Wraps the three wires in the cable with extra insulation for safety
What is the cable grip of a plug for?
Holds the cable tightly so the wires don’t become loose
What is the live wire?
The brown plastic that coats a copper wire along which current enters the device
What is a fuse?
Glass or ceramic canister that has a thin wire that melts inside if current gets too high
What is a neutral wire?
Blue plastic plastic that coats a copper wire that connects to the cable in the wall and completes the circuit
What is the Earth wire?
Striped plastic coated copper wire that provides a path for current to flow from the case of device to ground if there is a fault
How does the Earth wire prevent the user from getting electrocuted?
The Earth wire is connected to the case and is attached to a water pipe underground
Because the wire is made of copper the Earth wire provides a low reisistnce path to the ground
So if anything goes wrong the live wire current passing through the case will pass through the ground instead of the person
How does a fuse work when a fault happens?
If there is a fault a large currrent will flow through the low resistance Earth wire
This causes the fuse to melt
Since the fuse is melted the circuit is broken and no more current flows through the device
What does the national grid do?
Distribute electricity across the county
How is electricity in national power grid produced?
With a generator or another method
What are transformers used for?
Used to change voltages and currents in transmission lines
How are transformers made?
Two coils of wire around a magnetic core
What does the number of coils on a transformer determine?
If it’s a step up or step down transformer of voltage
What happens to current as voltage increases?
Is decreases current
What happens to voltage as current increases?
It decreases voltage
What does a step up transformer do?
Increases voltage and reduce current
How much does a step up transformer increase voltage and what does this do?
25000V-400000V causing current to decrease
Meaning less energy is lost through heating the wire
What is used to keep high voltage wires safe from people?
Pylons to keep transmission lines above the ground
How much does a step down transformer reduce voltage by?
230V
What happens to transmission lines as electric current flows through it?
Electrons flow through the cable and they get hot and dissipate energy to the surroundings
How do you ensure minimal power is lost from the cables?
Make cables are thick so resistance is low
High voltages are used to reduce the current through the transmission lines
How does having a low resistance and low current affect power delivered to consumer?
The wires won’t heat up as much so most of the power is delivered to the customer
