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FIND OUT MORE. Chemistry 162 • Electricity 182 • Electricity Supply 187 • Electromagnetism 186

The different objects that make up a circuit

are called components. A circuit must have

a power source, such as a battery, and the

current flows through a conductor, such

as a wire. Bulbs, buzzers, and motors are

components that change electricity into

light, sound, and movement.

WHAT IS A CONDUCTOR?

A material that carries a current well is called a

conductor. Metals are good conductors because metal

atoms readily release electrons to carry the current.

Silver and copper are the best conductors, and most

electric wires are made from copper. To prevent

electric shocks, wires are covered

with an insulator.

WHAT IS AN A INSULATOR?

Some materials do not carry current well. They are

said to resist (oppose) the flow of current. Materials

that do this are called insulators. Plastics, glass,

rubber, and ceramics are all good insulators. Insulators

are used to cover wires and components to prevent

electric shocks, and to stop currents flowing.

HOW DOES A SWITCH WORK?

Switches are like gates that control the flow of

electricity in a circuit. When a switch is open, it

creates a gap in the circuit and current will not flow.

When it is closed, it completes the circuit, and current

flows through it. Switches are used in parallel circuits

to turn different parts of the circuit on and off.

WHAT IS MAINS ELECTRICITY?

Most of the electricity we use in our homes and

workplaces is mains electricity. Mains electricity

is produced by machines in power stations called

generators. Generators send electric current through

a huge network of circuits spread around the country.

4 HEART PACEMAKER

The battery and other components

of an artificial heart pacemaker

send electric pulses through wires

to a patient’s heart to keep it

beating steadily. A pacemaker is

fitted when the heart does not

beat steadily by itself.

Voltage is the energy given to

each unit of charge

that flows in a circuit

Current is the amount of

electric charge

flowing past a

point in a circuit

each second

Wattage is the amount

of electrical energy

a circuit uses

each second

POWER INSULATORS 3

Mains electricity travels around the country in wires called power lines.

Giant ceramic insulators prevent the current flowing to the ground.

COMPONENTS

Decorative

metal ring

bounces ball

away

Heavy steel ball

operates switches

with its weight, or by

completing a circuit

Bulb inside

bumper unit

lights up

when the ball

activates a switch

CIRCUIT DEFINITIONS