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FIND OUT MORE. Circuits 184–185 • Electricity 182 • Magnetism 183

186

An electric current produces magnetism, and a magnet

can produce an electric current. The two forces are so

closely connected that scientists talk about the single

force of electromagnetism. Without it, we would not

have an electricity supply, or. ELECTRIC MOTORS.

HOW DOES ELECTRICITY CREATE MAGNETISM?

Each electron is surrounded by a force called an electric field. When an electron

moves, it creates a second field – a magnetic field. When electrons are made to

flow in a current through a conductor, such as a piece of metal or a coil of wire,

the conductor becomes a temporary magnet – an electromagnet.

HOW DO ELECTRIC MOTORS WORK?

A current turns a conductor into an electromagnet.

If the current is reversed, the electromagnetic poles

will reverse, too. When the electromagnet is placed

near to a fixed magnet, the two sets of poles repel and

attract each other. This produces a force which makes

the conductor rotate (spin) at high speed. This turns

a shaft which then drives a machine.

WHAT DO GENERATORS DO?

Generators supply us with most of the electric current

we use. They turn mechanical energy (movement) into

electrical energy. Inside a generator, a coil of wire is

spun inside a powerful magnetic field. This creates an

electric current in the wire. A large generator can

produce enough electricity to run an entire city.

HOW DOES MAGNETISM PRODUCE ELECTRICITY?

If a coil of wire is placed near a magnet with an

unchanging magnetic field, nothing happens. But if

the magnetic field is changed, by moving the magnet

back and forth, or spinning the wire, the changing

magnetic field produces an electric current in the wire.

Electric motors are machines that turn

electrical energy into mechanical energy to

do work. Electric motors can be small, like

the motor that turns the fan in a hairdryer,

or huge, like the engine that drives a train.

4 METAL DETECTOR

A metal detector makes use of

electromagnetic effects to find

metal landmines hidden under

the soil. Wire coils in the detector

produce a changing magnetic

field, which induces (causes)

electric currents to flow in the

metal landmines. These in turn

produce magnetism that can be

sensed by the detector.

Electromagnetism

1 MICRO MOTOR GEARS

In 1960, engineer William

McLellan built a motor the size of

a full stop from 13 separate parts.

Today, engineers are trying to

build motors thousands of times

smaller. This picture of motor

gears is magnified 200 times.

4 ELECTROMAGNET

Unlike permanent magnets,

electromagnets can be switched

on and off. This is useful in a

scrapyard, where a powerful

electromagnet separates iron and

steel scrap from other materials.

ELECTRIC MOTORS

Non-magnetic scrap

is left behind

Iron and steel scrap

is attracted by the

magnet when it is on

Electromagnet

hangs from

chains

Cable carries

electric current

Crane jib

moves magnet

into place

electromagnet