10.1.1 Magnetism — Edexcel GCSE Combined Science 1SC0 - Physics Revision Notes & Topical Questions

Section 1 of 9Poles and the law of magnetism

Every magnet has two poles, a north-seeking pole (N) and a south-seeking pole (S). The poles are where the magnetic effect is strongest, usually near the ends of a bar magnet. If a bar magnet is suspended so that it can turn freely, it comes to rest pointing roughly north-south. The end that points north is the north pole.

The law of magnetism states: like poles repel, unlike (opposite) poles attract. Two north poles push apart; a north and a south pole pull together. The force between two poles gets weaker as the distance between them increases, and acts without contact, which is why magnets are said to act through a field.

Section 2 of 9Testing for a magnet: repulsion, not attraction

Both poles of a magnet attract an unmagnetised piece of iron, so attraction alone does not prove that something is a magnet.

Repulsion

The only reliable test for a magnet is repulsion: if an object is repelled by a known pole, it must be a magnet,

because only a magnet can have a pole of the same type.

Attraction means the object is either a magnet (with an opposite pole facing) or a magnetic material that has become temporarily magnetised.

Section 3 of 9Magnetic materials

Only a few materials are magnetic, meaning they are attracted by a magnet and can be magnetised.

1Iron, steel, nickel and cobalt

The common ones are iron, steel, nickel and cobalt, and some of their alloys.

2

Copper, aluminium, plastic, glass, wood and most other materials are non-magnetic.

3

Note that steel is magnetic because it is mainly iron, but stainless steel varies; most pure metals are not magnetic.

4

Magnets do not attract most metals, so a magnet cannot be used to separate aluminium from copper but can pick out iron or steel objects from rubbish.

Section 4 of 9Magnetically hard and soft materials

	Magnetically soft	Magnetically hard
Example	Iron (soft iron)	Steel, alloys such as alnico
Magnetising	Easy and quick	More difficult
Demagnetising	Loses magnetism easily	Keeps its magnetism
Use	Cores of electromagnets, transformers, relays	Permanent magnets, compass needles

The difference is due to how easily the tiny regions inside the material (domains) can be lined up and whether they stay aligned afterwards.

Section 5 of 9The magnetic domain picture

Inside iron there are microscopic regions called domains, each acting as a tiny magnet.

1

In an unmagnetised piece the domains point in random directions and their effects cancel.

2

When the iron is placed near a magnet or inside a coil carrying current, the domains line up, and the iron becomes a magnet.

3

Hammering, heating or dropping a magnet can jumble the domains and so weaken or destroy its magnetism.

4

Cutting a magnet in half does not separate the poles; each half becomes a smaller magnet with its own N and S pole.

Section 6 of 9Everyday uses

1

Fridge magnets and door catches (permanent magnets, hard materials).

2

Compasses: a small, freely pivoted magnet aligns with the Earth's field.

3

Cranes in scrap yards: electromagnets that can be switched on and off to lift iron and steel.

4

Credit-card stripes and loudspeakers.

Link to 6.1.2 for how we picture the force around a magnet using field lines.

Magnetic force and distance

The force between two magnets depends on how far apart they are.

Everyday uses

Bring two magnets slowly towards each other and the push or pull is barely noticeable at 10 cm but is strong at 1 cm.

The force falls off quickly with distance, which is why a magnet can pick up a nail only when it is very close.

Magnets also exert forces on magnetic materials through non-magnetic materials such as paper, wood or thin plastic,

which is how a fridge magnet holds a sheet of paper to a steel door.

The force between poles is a field effect: each magnet creates a magnetic field in the space around it and the other magnet feels the force of that field (see 6.1.2). Because the effect is a property of the field it does not require the magnets to touch.

Section 7 of 9Worked examples

A student has three identical-looking metal bars, A, B and C. A attracts B, A repels C and B attracts C. Which, if any, are magnets?
A scrapyard has to separate a mixed pile of iron nails, aluminium cans and copper wire. Describe how a magnet can help and what remains.

Section 8 of 9Key terms

Term	Meaning
Pole	Region of a magnet where the magnetic force is strongest.
Magnetic material	Material attracted by a magnet, such as iron, nickel and cobalt.
Magnetically soft	Easily magnetised and loses magnetism easily.
Magnetically hard	Hard to magnetise but keeps its magnetism.
Domain	Microscopic region in a material that acts as a tiny magnet.

Section 9 of 9Exam technique

1

Saying that a magnet attracts all metals: only iron, steel, nickel, cobalt and some alloys.

2

Believing attraction proves magnetism. Only repulsion does.

3

Thinking cutting a magnet separates the north from the south pole.

4

Mixing up 'soft' with weakmagnetically soft means easily magnetised and demagnetised.