P2.4 (mains electricity) Flashcards
What is DC?
DC stands for direct current
In a direct current the current flows in one direction only
All battery powered portable TV devices
Typically 1.5 V
What is AC?
AC is alternating current Frequency of 50hz 230 v Constantly changes direction Mains electricity is an AC supply
Why do mains electricity cables have a core of copper?
Copper is a good conductor of electricity
Why do mains electricity cables have an outer layer of plastic?
The plastic is flexible and a good insulator.
Within a wire, what colours are the three wires?
Blue, Brown, Green + Yellow stripes
What do the blue, brown, yellow + green striped wires mean?
Blue = neutral Brown = live g+y = earth
What are the features of a plug?
Tough plastic/rubber case –> good electrical insulators
Three brass pins –> good conductor of electricity
Fuse between live terminal and live pin (breaks the circuit if too much current flows)
Cable secured by cable grip
Where do the three wires connect inside the plug?
bLue -> to the Left
bRown -> to the Right
sTriped -> Top
What are RCCBs?
Residual current circuit breakers detect a difference in current between live and neutral wires.
They work faster than fuses
What is earthing?
Earthing is used in electrical appliances with a metal casing such as cookers and dishwashers. You would get an electrical shock if the live wire was to come loose and touch the casing, and so the earth wire is connected to the casing itself as well and the current flows through it. The earth wire has a very low resistance and so a large current passes through it causing the fuse to burn out and disconnect the appliance.
What is double insulation?
Double insulation is in appliances that do not have an earth wire as the appliance eg a vacuum cleaner/electric drills has been designed so the live wire cannot touch the casing or they have a plastic casing.
What is the period of an AC supply?
The time it takes for one complete oscillation
This can be calculated by the distance between two peaks / troughs / identical areas on the graph
What is the frequency of an AC supply?
The frequency is the number of oscillations per second
It can be calculated by frequency = 1 / period (in seconds)
UK mains frequency is 50hz
What is the relationship between energy transfer, power, and time?
Energy transfer (kWh) = power (kW) x time (hour)
How do you convert from watts to kilowatts?
divide by 1000
