(2.2-2.6) Mains electricity

What are the three wires in a plug? What are their normal colours?

live wire- brown

earth wire- green/yellow

neutral wire- blue

What does the live wire do?

alternates between a high +ve and -ve voltage of 230V

What does the neutral wire do?

stays at 0V

What does the earth wire do?

reduces the risk of electric shock in non-metal casing appliances as earthed conductors can never become live.

Why do domestic appliances need to be modified to protect the user?

risk of:

electrocution- exposed wire

fire- overheating wire, moisture in contact with live wires

How does insulating a domestic appliance help safety?

conducting, metal parts of wires can electrocute.

covering any wires with insulators- like rubber, reduces risk.

How does double insulating a domestic appliance help safety?

wire and the appliance are both enclosed by insulators.

when an appliance doesn’t have a metal case, there’s no risk of the case becoming electrified.

How does earthing a domestic appliance help safety?

when a fault occurs,

earth wire provides low resistance path to earth

surge of current in earth and therefore live

high current blows fuse

cuts off electricity supply to the appliance

What is a fuse?

a glass cylinder containing a metal wire that can only withstand a certain current before melting

How does a fuse in a domestic appliance help safety?

when current exceeds limit, it blows, cutting off the flow of electricity to an appliance

What is a circuit breaker?

an automatic electromagnet switch that breaks the circuit

How does a circuit breaker help safety? Is it better or worse than a fuse?

it can quickly cut off electricity to appliances and be reused. Faster and more practical that a fuse.

Why does heat increase when current passes through a resistor?

this is an energy transfer pathway.

collisions of free electrons within the wire

lead to an increase in energy

some of which is dissipated into the surroundings by heating

When a resistor's heat increases, as does its…?

its resistance

What is power?

the rate at which an appliance transfers energy

How do you calculate energy transferred?

the electrical power of an appliance * how long it’s been running

State formula for P

power = current * voltage

P=IV

Formula for energy transferred.

voltage*current*time

E = IVt

What is direct current?

a steady current, produced by cells/batteries, flowing in the same direction, from a constant positive to constant negative terminal

What is alternating current?

a current, produced by electrical generators, that continuously change direction, alternating between two identical terminals that change from + → - etc.

a.c always goes form p → n so, as polarity changes, as does the current

What is the frequency of a.c?

the number of time the current changes direction per second.