the amount of energy transferred each second

the unit of power; equal to the number of joules of energy transferred each second

a unit of power; 1 kilowatt is equal to 1000 watts

a thin wire that melts when a dangerously large current flows through it

Power of an appliance or electric circuit

Combined science

Danger from electric shock

Short circuits and earth wires

Calculating with electric charge

The National Grid

Energy resources

In the Circuit components unit, pupils learnt how the resistance of filament lamps and diodes change with current and about the properties and applications of light dependent resistors and thermistors.

This unit covers UK domestic a.c. supply, mains wiring safety, energy changes in electrical systems, power ratings, and energy transfer. It explains the National Grid, transformers, energy sources, and calculations for energy changes and power transmission efficiency.

Mains electricity

A lamp has power of 7 W. Which of the following explains what this means?

When an iron is working correctly, the current through it varies between 1.6 A and 3.3 A. Which of the following fuse sizes should be used in the plug of this iron?

too many appliances being connected in series

too many appliances being connected in parallel

Which of the following could cause a circuit breaker to switch off a circuit?

The current through a lamp is 1.5 A and the p.d. across it is 12 V. The power of the lamp is {{}} W.

What is the current through a 600 W lawnmower that is plugged into the mains?

A 1300 W iron and a 1000 W hairdryer are plugged into a mains circuit, in parallel. What is the current through a circuit breaker in the consumer unit?

Which of the following are ways of writing the definition of power?

A mains circuit includes a fuse. Which of the following makes a fuse ‘blow’?

What is the potential difference across the resistor in the circuit shown?

What is the missing current in the circuit shown?

A cell is connected to a lamp and a current flows. What happens to the current through the cell if another lamp is added in parallel with the first lamp?

An ammeter shows that the current through a resistor is 0.40 A and a voltmeter shows that the p.d. across it is 1.5 V. A pupil calculates the resistance. Which of these answers should they give?

Power of an appliance or electric circuit

Lesson outcome