Types of magnets and magnetic fields

In a nutshell

Magnetic materials such as iron, nickel and cobalt are examples of permanent magnets. Magnets create magnetic fields around them, which are regions of space where other magnetic materials will experience a force. Magnetic poles are where the magnetic field lines are most concentrated. Opposite magnetic poles attract and similar magnetic poles repel.

Types of magnets

There are different types of magnets, there are permanent magnets, electromagnets and temporary magnets. Permanent magnets and temporary magnets, as the name suggests, are magnets which stay magnetic or lose their magnetism relatively quickly.

Electromagnets are a special type of temporary magnet which can have a variety of strengths, shapes and sizes. Electromagnets can be switched on and off.

There are three main elements which have magnetic properties, which are iron, nickel and cobalt. Some alloys of iron such as steel will also show magnetic properties. Copper and aluminium are examples of metals which are not magnetic.

Magnetic fields

Magnetic fields are non visible force fields which are created by magnets. They are regions in which other magnetic materials will experience a force. Along with electric fields and gravitational fields, they are also a non-contact force. This means that the objects do not need to touch in order to experience the force.

Field lines

Magnetic field lines can be drawn around a bar magnet. A bar magnet is a simple permanent magnet with two magnetic poles. A magnetic pole is where the magnetic field is the strongest.

The field lines for a bar magnet looks like this. Magnetic field lines always point away from the north pole (N) and points towards the south pole (S).

Curiosity: It is impossible for a magnet to exist with only one pole.

How magnets interact

When two magnetic poles are bought together one of two things can happen.

magnet_attract — When two opposite magnetic poles are brought together, the field lines can flow out of one pole and straight into the next one. This will cause the magnetic poles to attract and will experience a force which brings them closer together.

magnet_repel — When two similar poles are brought together, the field lines start to push against one another. This will be experienced as a repulsive force and the magnets will push each other apart.

Curiosity: Magnetic field lines cannot intersect one another, which means they cannot pass over one another.

Earth's magnetic field

The Earth has a solid iron core which is surrounded by a molten iron shell. As the liquid iron moves around the solid core it creates a large magnetic field and its field lines protrude into space. This is called the dynamo effect.

The Earth's magnetic field and its field lines which surrounds the Earth.

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Spin axis

Science; Magnetism; KS3 Year 7; Types of magnets and magnetic fields

Curiosity: Earth's geographical North pole is actually a magnetic South pole, which is why the field lines flow out of the geographical South pole into the geographical North pole.

Compasses

Compasses are instruments which are made up of a suspended magnetic needle which is free to turn around in a casing. As the compass is rotated the needle stays aligned with the Earth's magnetic field lines and always points towards North.