Mains Electricity Flashcards
What is direct current?
Electric current in a circuit that is in one direction only.
What is an alternating current?
Electric current in a circuit that repeatedly reverses its direction.
What is the frequency?
The number of wave crests passing a fixed point every second.
What is the unit for frequency?
Hz
What is the peak voltage of an alternating potential difference?
The maximum voltage measures from zero volts
What is the mains frequency in the UK?
50Hz
What is the live wire?
It is alternatively positive and negative every cycle.
What is the neutral wire?
- it’s earthed at the local substation.
* it is at zero volts.
What is an oscilloscope?
A device used to display the shape of an electrical wave.
How do we use an oscilloscope to measure the frequency of an alternating current?
Measure the time period of the waves then use the formula:
Frequency = 1 / time for one cycle
What does the live wire alternate between?
+325V and -325V
Where is the earth wire connected to?
The ground at your home.
Why is there a longer pin of a three-pin plug?
It makes contacts with the earth wire of a wall socket circuit. When you plug an appliance with a metal case to a wall socket, the case is automatically earthed.
Why are sockets and plugs made of stuff plastic materials?
Plastic is a good electrical insulator.
Why are the pins made out of brass?
- it is a good electrical conductor.
* it does not rust/oxidise.
Why isn’t copper used instead of brass?
It isn’t as hard as brass although it conducts better.
Why is there a fuse in the plug?
If too much current passes through the wire in a the fuse, it melts and cuts the live wire off.
What colour is the live wire?
Brown.
What colour is the neutral wire?
Blue.
What colour is the earth wire?
Yellow and green.
What is the difference between a three-core cable and a two-core cable?
A two-core cable does not have an earth wire.
Why is copper used for the wires?
- good electrical conductor.
* bends easily.
Why is plastic used to surround the copper wires?
It is a good electrical insulator so it prevents anyone touching the cable from receiving an electric shock.
What are two-core cables used for?
Appliances with plastic cases.
