a complete circuit with a very small resistance, often caused by a loose wire

two layers of electrical insulation, including the outer casing of an appliance

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

a wire connected between a metal casing and the ground (0 V)

a switch that is turned off by an electromagnet when a dangerously large current flows through it

Short circuits and earth wires

Combined science

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

Some electrical appliances have two layers of electrical insulation: the plastic around the wires, and an insulating outer casing. This is called {{}} insulation.

The diagram shows three electric circuits. How many of these have a short circuit?

If it switches on, it needs to be replaced.

A wire inside it melts if the current is too high.

Which of the following statements about a circuit breaker are correct?

always, whether the appliance is switched on or off

if the live wire comes loose and touches the metal casing

if the earth wire comes loose and touches the metal casing

When does current flow in the earth wire of an appliance that has a metal outer casing?

the insulation around the wires in the appliance

Which of the following is the earth wire of an appliance connected to?

It breaks the circuit if the current is too large.

It is used as a switch to turn a circuit on and off.

It provides a low resistance path for current to flow to earth.

Which of the following is the purpose of a fuse?

The electricity from sockets and circuits in a home is called {{}} electricity.

Which of the following are good electrical insulators?

Which of the following are names of wires in appliances that are plugged into sockets at home?

Which of the following causes pain or injury during an electric shock?

The wires usually have much less resistance than the components.

The wires usually have similar resistance to the components.

The wires usually have much more resistance than the components.

Which of the following statements about wires in a circuit is correct?

There is a large resistance between the two wires.

There is a small potential difference between the two wires.

There is a large potential difference between the two wires.

A person touches a live wire with one hand and a neutral wire with the other hand. Which of these statements explain why they get an electric shock? 

Introduction

What will you need for this lesson?

Are you ready to learn?

Equipment

Worksheet