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Electricity - Mains Electricity
A 3-pin plug is used to connect electrical appliances to a mains socket in the UK.

Electricity - Mains Electricity

Mains electricity is the phrase used to refer to the general-purpose 230 V AC electricity supply, as opposed to the specialist higher voltage industrial electricity supplies. You can regard it as the electricity that is supplied to normal wall sockets, lighting circuits etc. in homes and places of work like offices and shops. In GCSE Physics, mains electricity is focused on electricity in the home. Mains electricity is useful but, if used incorrectly, it can be deadly, so understanding this form of energy and how to use it safely is a very important life skill.

Any form of electricity is a source of energy which can be transferred into other forms of useful energy. There is usually at least one form of waste energy during any energy transfer. With home electrical appliances, it's a good bet that this waste energy will be heat (unless it is an electric heater of course!). This means that no appliance will ever be one hundred percent efficient, but some come quite close.

1.
Which colour wire is the live wire in a 3-pin plug?
Blue
Yellow and green
Brown
Red
The blue wire is the neutral wire, yellow and green is the earth wire and the brown wire is the live wire
2.
What does the power of an electrical appliance represent?
The amount of current that passes through the appliance
The rate at which it transforms energy
The speed at which it performs a task
The size of voltage that the appliance uses
An appliance that transfers one joule of electrical energy per second has a power of one watt
3.
What kind of a plug is used to connect electrical appliances to a mains socket in the UK?
2-pin plug
3-pin plug
4-pin plug
5-pin plug
2-pin plugs are found on low power items. They either need an adaptor or have a 'dummy' earth pin made out of plastic so that they can be used directly with a normal wall socket
4.
Why do some appliances not need an earth wire?
These appliances do not need an earth wire as they don't use electricity
They are double insulated so that shocks cannot be caused if the appliance malfunctions
They have been incorrectly wired
All appliances need an earth wire, some do not have a neutral wire
Double insulation of appliances is designed to make sure that, in normal use, it is not possible for the electricity to come into contact with the outer casing
5.
If an appliance uses mains electricity at 230 V and the service manual for the appliance recommends using a fuse of 13 A, what is the power consumption it can safely use?
2020W
2550W
2990W
3520W
Power (in watts) = current (in amps) multiplied by the potential difference (in volts). Fuses allow the appliance to operate at a safe capacity. If there is a power surge through the appliance, the fuse will break the circuit stopping an unsafe level of electricity flowing through the appliance which could either damage the appliance or cause an electric shock
6.
Most appliances have their power consumption and potential difference printed on them. Which of the following can be calculated from these values?
Internal resistance of transformer
Momentum
Current
Work done
The ability to calculate the current that the appliance uses allows us to correctly identify which fuse should be used in the plug, to ensure any electrical surges are prevented from damaging the appliance or posing safety risks
7.
What do electrical appliances transfer?
Chemical energy
Electrical energy
Light energy
Sound energy
Appliances convert electrical energy into other forms of energy
8.
Some cables for electrical appliances only have two wires within them. Which wire is missing from this configuration?
Earth
Neutral
Live
The red one
This is used normally for low power items like smartphone chargers, bedside lamps and items whose casing is made entirely from plastic
9.
What is the main difference between a circuit breaker and a fuse?
A circuit breaker can be used to control electrical circuits
A circuit breaker can be reset whilst a fuse needs to be replaced
A fuse can be reset whilst a circuit breaker needs to be replaced
A fuse can be used to control electrical circuits
They also respond much faster than fuses and are generally used to protect complete circuits that are fitted with several sockets or lights
10.
What size of fuse would be required for an electrical appliance which has a power rating of 600W and running off UK mains voltage at 230V?
1 A
2.5 A
3 A
5 A
600 W divided by 230 V = 2.61 A so you choose the next highest standard fuse
You can find more about this topic by visiting BBC Bitesize - Mains electricity

Author:  Martin Moore

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