Mains electricity

What are the risks of electrical devices?

- electric shocks from contact with exposed live wires

- fires & burns from overloaded circuits & current that it is too high

- tripping hazards from trailing cables

- shocks & malfunctions from damaged equipment & when water comes into contact with electricity

How can the device & user be protected from potential risks?

- insulation & double insulation

- earthing

- fuses

- circuit breakers

How does insulation & double insulation protect the device & user?

- insulation (e.g. plastic) covers exposed wires & absorbs any heat that is produced from the circuit

- this protects the user from electric shocks & burns

How does earthing protect the device & user?

• the earth wire is connected to the casing of the appliance

• so if the live wire touches the appliance casing, the earth wire provides an alternative path for electricity to flow

• this ensures that people don’t get electric shocks when in contact with the live appliance casing

How do fuses protect the device & user?

- fuses stop the flow of current if it gets to high by melting

- this protects the device from fires caused by components functioning at a too high temperature as well as protecting the user from burns

- fuses are easy & cheap to replace

How do circuit breakers protect the device & user?

- circuit breakers stop the flow of electricity if a fault is detected or the current is too high

- this prevents the device from overloading & short circuiting which could lead to a fire

- circuit breakers act faster than fuses & can be reset, rather than needing replacement

What happens when current flows through a resistor?

- the resistance causes some the electrical energy to transfer to heat energy

- some components are designed to make sure sure this happens (e.g. electrical heaters have a lot of resistors to ensure that a lot of heat is produced due to the high resistance)

What is the formula linking power, current & voltage?

power = current × voltage

P = I × V

What is the formula linking energy transferred, current, voltage & time?

Energy transferred = current × voltage × time

E = I × V × t

What is the difference between alternating current & direct current?

- alternating current (a.c.) is constantly changing magnitude & direction whereas direct current (d.c.) only flows in 1 direction

- alternating voltage produces alternating current

- direct voltage produces direct current

What is mains electricity?

- the electricity that is delivered to homes & businesses through an electric grid

- it is an alternating current supply

- in the UK, mains electricity has a frequency of 50Hz & 230V