Supplying Electricity Flashcards
(25 cards)
What is a dc?
Direct current
What is an ac?
Alternating current
What happens in a cell or battery?
- Direct p.d. induced
- Dc provided -> only flows in one direction
What happens in mains electricity?
- Alternating p.d. induced
- Ac provided -> current repeatedly changes direction.
How is a cell/battery different from mains electricity?
Cell/battery -> dc, direct p.d.
Mains -> ac, alternating p.d.
What is the frequency of mains electricity in the UK?
50Hz
What is the voltage of mains electricity in the UK?
230V
Plugs: what colour is the Earth wire?
Green and yellow striped
Plugs: what colour is the live wire?
Brown
Plugs: what colour is the neutral wire?
Blue
What does the Earth wire do?
It is a safety wire to stop the appliance becoming live.
What is the p.d. of the Earth and neutral wires?
0V
When does the Earth wire carry a current?
ONLY if there is a fault
What does the live wire do?
It is connected to the fuse, melts it to keep safe
What happens when an appliance short circuits?
- Live wire touches the neutral wire
- Which causes a large current (230V) to flow
- The fuse melts and disconnects the live wire from mains -> keeps it safe
Why is the live wire dangerous?
It has a large p.d. of 230V, which would induce a dangerously high current if it was touched.
Why is copper used for the wires in a plug?
It is a good conductor of electricity and bends easily
Why is plastic used for the wire coatings and case in a plug?
It is a good electrical insulator
What is the National Grid?
A nationwide network of cables and transformers that link power stations to homes, offices, etc.
What is a transformer?
Devices that can change the p.d. of an ac.
What do step-up transformers do?
Increase the p.d. from the power station to the transmission cables
What p.d. do power stations generate electricity at?
An alternating p.d. of around 25,000V
What voltage do the cables in the National Grid transfer electricity at?
About 400,000V
What do step-down transformers do?
Decrease the p.d. from the transmission cables so it is safe to use
