Supplying Electricity Flashcards
What type of current does a cell or battery provide?
A direct current (dc)
Which way does a direct current flow and what is it produced by?
- Only flows in one direction
- Produced by a direct potential difference
What type of current does mains electricity supply?
An alternating current (ac)
Which way does an alternating current flow and what is it produced by?
- Repeatedly reverses directions
- Produced by an alternating potential difference
What happens to the positive and negative terminals of an alternating power supply?
They swap over with a regular frequency
What is the frequency of the UK mains electricity supply?
50Hz
What is the voltage of the UK mains electricity supply?
230V
What is the Earth wire?
- A safety wire to stop the appliance becoming live
- Potential difference is 0V
- It only carries a current if there is a fault
- Green and yellow
What is the neutral wire?
- Completes the circuit
- Potential difference is 0V
- Blue
What is the live wire?
- Dangerous because it has a high potential difference of 230V
- Brown
- Cause a large current to flow through you if touched
What metal is used for most wires in the UK and why?
- Copper
- Good electrical conductor
- Bends easily
What is used for the wire coating and why?
- Plastic
- Good electrical insulator
What is a short circuit?
A very large current flowing if the live wire touches the neutral wire
What happens when something short circuits?
The fuse melts and disconnects the live wire from the mains, keeping the appliance safe
What is the national grid?
A nationwide network of cables and transformers that link power stations to homes, offices, and other consumers of mains electricity
What are transformers?
Devices that can change the potential difference of an alternating current
How much potential difference of electricity do power stations generate?
An alternating potential difference of about 25,000V
What are step-up transformers used for?
To increase the potential difference from the power station to the transmission cables
What do the cables in the National Grid transfer?
Electrical power at a potential difference of up to 400,000V
What do step-down transformers do?
To decrease the potential difference from the transmission cables to the mains supply in homes and offices so that it is safe to use
What does a high potential difference across the transmission cables mean?
A lower current is needed to transfer the same amount of power
What does a lower current in the cables mean?
- Less electrical power is wasted due to heating of the cables
- This makes the National Grid an efficient way to transfer energy
What happens when you turn an electrical appliance on?
The potential difference of the mains supply causes charge (carried by electrons) to flow through it
