P4 - Safe electricals Flashcards
What is electric current?
The rate of flow of electric charge.
How does a resistor work?
Adding a resistor to a circuit reduces the flow of charge so the current is smaller.
What affects the resistance?
- longer wires (increased distance for charge to travel)
- thinner wires (less space for current to pass through)
What is resistance measured in?
Ohms.
A piece of wire has a resistance of 3 ohms and melts if the current exceeds 5A. What is the maximum voltage across the wire without melting it?
V = I x R
3 x 5 = 15V
What are the two wires connecting a house to a power station?
- live
- neutral
What are the colors for the following wires:
- live
- neutral
- earth
Live: brown
Neutral: blue
Earth: green/yellow striped
What does the live wire do?
The live wire carries a high voltage into and around the house.
What does the neutral wire do?
The neutral wire completes the circuit, providing a return path for the current to the loves electricity sub-station.
What does the earth wire do?
The earth wire is a safety wire. There is no current in it and it is attached to the metal casing.
How does a fuse work?
1) there is suddenly a large current in the live and earth wires
2) a fuse melts when the current becomes too large, stopping the flow of charge
3) as the fuse is in the live wire, the appliance is now disconnected from the mains supply
How does double insulation work?
A double-insulated appliance does not need an earth connection. It has a plastic case with no electrical connections to it so the case cannot become live.
