Childrens Illustrated Encyclopedia

329

Origin Of magnetism

iron contains millions of tiny

magnets called magnetic domains.

normally, all of the domains point

in different

directions,

so their

magnetism cancels out. in

a magnet, the domains point

the same way so that their

magnetism combines.

the fOrce of magnetism is

invisible, yet you can see its power

when a magnet drags a piece of

metal toward it. a material that

attracts certain metals, such as

iron, is called a magnet. materials

that are attracted by a magnet are

called magnetic. every magnet has two

poles—places at which magnetic objects

cluster. earth itself is a huge magnet;

its magnetic poles are close to the geographical

north and south poles. One pole of a magnet is

attracted to earth’s northern magnetic pole and is

called the magnet’s north pole; the other is attracted to

the south and is called the magnet’s south pole. materials

that retain their magnetism all the time are called permanent

magnets. an electric current flowing in a coil of wire produces

a magnet called an electromagnet

that can be switched on and

off. electromagnets are used in

electric motors, loudspeakers,

and many other devices.

magnetic field

the area around a magnet in which

its magnetic force works is called

its magnetic field. for instance,

a paper clip is pulled toward

the magnet (right) when it is

placed within the magnetic

field of the magnet.

All magnets attract

iron and steel

objects but not

plastic or

wooden

ones.

Magnetism

Magnetic poles

A magnetic pole, such as a

south pole, repels (pushes away)

another pole of the same kind.

NS SN

NSSN

The north pole of one magnet

and the south pole of another

magnet attract each other.

cOmpass

the needle inside a magnetic compass is

a thin, light magnet, balanced so that it

swings freely. the needle’s north pole

points toward earth’s magnetic north

pole, which is very close to

the geographical north. people

use magnetic compasses to

navigate at sea and on land.

The pattern of lines shows

Earth’s magnetic field. The

field is strongest where the

lines are closest together.

electrOmagnets

an electromagnet is a coil of

wire. an electric current within

the coil creates a magnetic

field. the field can be made stronger by winding

the wire around a piece of iron. turning off the

current switches off the magnetic field. some

cranes use an electromagnet instead of a hook.

The geographical North and South

poles lie on Earth’s axis, which is the

line around which Earth spins.

geOmagnetism

earth produces a

magnetic field that makes

it seem as though it has a 

huge “bar” magnet inside it.

electric currents flowing within

earth’s liquid iron core cause

earth’s magnetism, which is

called geomagnetism.

The magnetic north

and south poles lie a

small distance away

from geographical

North and South.

lOdestOne

magnetite is an

iron ore that

often possesses

magnetism. it was

once commonly

called lodestone, which

means “guiding stone,”

because early navigators

used it as a compass.

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