2b: Mains electricity

2 types of electricity

- static electricity
- current electricity

hazards of mains electricity

- damaged insulation
- overheating of cables
- damp conditions

safety features built into domestic appliances

- double insulation
- earthing
- fuses
- circuit breakers

power

the rate of energy transfer or the amount of energy transferred per second

what is power dependent on

voltage and current

relationship between power, current and voltage

power = current x voltage

unit of power

watts

fuse

a safety device that cuts off the flow of electricity to an appliance if the current becomes too large

what do the ratings on a fuse tell us

how much current it can withstand

what does exceeding the current rating on a fuse cause

the fuse blows

should the fuse have a current rating higher than the current needed

yes

what will a low fuse current rating do

it will break the circuit even when an acceptable current is flowing through

what will a too high fuse current rating do

it will not be breaking the circuit in enough time before damage occurs

insulation

wires are covered with an insulating material as the conducting part of the wire is usually made of a metal that poses a risk of electrocution

double insulation

appliances with two layers of insulation

two layers of insulation in double insulated wires

- insulation around the wires
- a non-metallic cased

do double insulated appliances require an earth wire

no because the earth wire can't touch the metal casing

earthing

many electrical appliances have metal cases which poses a potential safety hazard if the live wire comes into contact with the case risking electrocution

how does the earth wire protects the user

the earth wire provides a low resistance path to the earth causing a surge of current causing the fuse to melt and break which cuts off electricity supply to the appliance

circuit breaker

an electromagnet switch that breaks the circuit if the current exceedds a certain value h

how does a circuit breaker work

it quickly shuts off electricity to the whole house

how is a circuit breaker better than a fuse

it doesn't melt and break and works much faster

DC

direct current

how does DC current travel

in one direction only

does a DC power supply have a fixed terminal

yes

AC

alternating current

how does AC current travel

it constantly changes direction

does an AC power supply have a fixed terminal

it has 2 identical terminals that switch between positive and negative

frequency of an alternating current

number of times the current changes direction back and forth each second

where is DC current produced/used

cells and batteries

where is AC current produced/used

electrical generators

when is work done

when charge flows through a circuit

relationship between work done and energy transferred

work done = energy transferred

relationship between energy transferred, current, voltage and time

energy transferred = current × voltage × time

why does temperature increase when electricity passes through a component

it's turned into heat

what is energy a transfer of

collisions between electrons flowing in the conductor and lattice of atoms within the metal conductor

current

flow of electrons

atomic configuration of metals

lattice of metals

what happens to electrons as they flow through metals

they collide with ions which resist the flow of electronsh

how does metal heat up

electrons collide and lose energy by giving it to ions which vibrate more

which appliances can the heating effect be utilised in

heaters, ovens, hobs, toasters, kettles