GCSE Physics P5 Electricity in the home,

Fuse

This component melts and breaks the circuit when too much current flows

Earth pin

The longest pin that connects first for safety, potential of 0V

neutral wire

This wire completes the circuit and carries away current (potential of 0V)

Live wire

This wire supplies the current, mains potential of 230V in UK

Explain where the fuse is located.

It is connected in the live wire so the supply is cut off if the fuse melts.

outer metal case. What is the Earth wire connected to? (not the pin!)

outer metal case.

Colour of the neutral wire

blue

Colour of the live wire

brown

Colour of the earth wire

green and yellow

alternating current (a.c.) and is supplied by what?

This current is constantly changing direction (supplied by the mains)

direct current (d.c.) and is supplied by what?

This current always flows in the same direction (supplied by cells and batteries)

what is the equation for power

= p.d. x current (P=VI)

what is the equation for energy?

=Power x time (E=Pt)

electrical energy transferred = (equation)

p.d. x charge (E=QV)

what is the equation for charge?

= Current x time (Q=It)

what is the equation for p.d.?

= current x resistance (V=IR)

current² x resistance =????

= Power (P=I²R)

what is the equation for efficiency?

= useful power output/total power input (x100%)

Units of resistance?

Ω

unit of power?

watts

units of energy?

joules

units of time

seconds

unit of current

amps

units of p.d.

volts

units of efficiency

% or ratio (decimal)

units of charge?

Coulombs

current in wires(or friction of moving parts) causes?

This causes heat energy loss in appliances

A smaller proportion of energy is wasted, higher proportion of energy is usefully transferred describe an appliance with a higher efficiency in terms of energy

A smaller proportion of energy is wasted, higher proportion of energy is usefully transferred

If a fault causes the outer metal case to become live, high current flows down the low resistance earth causing the fuse in the live to melt, stopping the current from flowing.

A smaller proportion of energy is wasted, higher proportion of energy is usefully transferred .

explain the meaning of double insulated?

The appliance has insulation covering the wires and the outer case so no earth wire is needed as the case cannot become live.

WHY do you get a shock from a live appliance?

There is a p.d. between you (0V) and the appliance (230V) so a current will flow through you to earth.

UK mains voltage?

230V

UK mains frequency

50Hz

what is a step-up transformer?

Increases the voltage (so decreases the current) in the national grid.

what is a Step-down transformer?

Decreases the voltage (so increases the current) in the national grid.

Why is energy transferred at a high voltage through the national grid?

For the same power, a high voltage means a low current. Low current means cables stay cooler so a smaller proportion of heat energy is wasted so the efficiency of the national grid is higher.

Describe 3-core cable

It has live, neutral and earth wires

Describe 2-core cable

It has live and neutral wires only, no earth is needed as the appliance is double insulated

What are plug pins plug are made of & why?

Brass: hard, strong and a good conductor

what is the plug outer case is made of & why?

Plastic: a good insulator so you don't get a shock

What are cables and wires are made from & why?

Copper: very good conductor of electricity

What is the national grid?

A system of cables and transformers linking power stations to consumers.

Why is the voltage stepped down to go into homes?

For safety to reduce the chances of an electric shock being fatal