P2.4 Mains electricity Flashcards
What is the voltage of the UK mains supply?
230 volts
What is the current of the UK mains supply?
50Hz
What type of current is the UK mains supply?
AC
What is ‘direct current’?
Current always passing in the same direction
What is ‘alternating current’?
Current constantly changing direction
Give one example of where direct current is used.
Batteries
How are most electrical appliances connected to the mains?
Using a cable and 3 pin plugs
What is the structure of a three core cable?
- Three wires inside them, each with a core of copper and covered with a coloured plastic coating:
- The live (brown) wire - transmits an alternating current
- The neutral (blue) wire - always at 0V
- The earth wire (green-yellow) wire - protects wiring and is for safety.
- It is covered with metal casing.
How does the earth wire ensure a safer cable?
It is connected to the casting of the appliance and the earth pin - it carries the electricity to the earth if any of the other wires touch the metal case.
What is the structure of a two core/double-insulated cable?
- It only has live and neutral wires
- The plug it is attached to is already covered in plastic so it doesn’t need an earth wire
Do all cables need an earth wire?
No, only metal cased plugs
How are three pin plugs wired?
- Green-yellow wire is connected to the earth pin
- Blue wire is connected to the neutral pin
- Brown wire is connected to the live pin
- No bare wires should be showing in the plug
- The cable grip is then fastened tightly over the cable outer layer
How does a fuse work?
It melts if the current gets too high (higher than its rating), cutting off the live supply and breaking the circuit
What rating of fuse should be used for an appliance?
One just higher than the normal operating current
What is the relationship between the thickness of a cable and fuse rating?
The larger the current, the thicker the cable thickness needed to carry it, so the higher the fuse rating.
What are RCCBs and how do they work?
- Residual Current Circuit Breaker
- It detects a difference between the live and neutral wire
- When there is a surge between them, it trips a switch and breaks the current.
What are the advantages of an RCCB?
- More sensitive
- Can be reset by flicking the switch on a device
- They don’t have to be replaced like fuses
- Much faster as no time is wasted waiting for the fuse to melt
What is the effect of electric charge flowing through a resistor?
- Electrical energy is converted to heat energy
- The more current flowing, the more heat produced
- A bigger voltage means more heating because it pushes more current through
Why do filament bulbs waste so much energy?
Filament bulbs work by passing a current through a very thin wire meaning more heat energy wasted
Define ‘power’ (of an appliance)
The rate at which it transforms energy/second
