Magnetic materials and forces between poles
Magnetic materials (attracted to a magnet and able to be magnetised): iron, steel, nickel, cobalt — name them; "metals" or "conductors" scores zero, and cobalt is the one most often forgotten. Other common materials (copper, aluminium, wood, plastic) are non-magnetic. Forces between poles: unlike poles (N–S) attract; like poles (N–N or S–S) repel. A magnetic field is a region in which a force acts on a magnetic pole — not merely "a region around a magnet".
Permanent vs induced; hard vs soft materials
Permanent magnet (retains its magnetism without an external field) — made from a hard magnetic material (steel), hard to demagnetise. Induced magnet (becomes magnetised in an external field and loses most of its magnetism when the field is removed) — made from a soft material (iron, nickel), easily magnetised and demagnetised. "Hard" means magnetically hard to demagnetise, NOT mechanically hard. Each definition needs both elements for full marks.
Magnetic field lines and plotting
Field lines run from N to S outside the magnet, form closed loops (S → N inside), never cross, and are closer together where the field is stronger (strongest at the poles). The field direction at a point is the way a compass north-seeking end points (N → S outside). Plot with a plotting compass: mark the needle's N-seeking end, step the compass along so its S end sits on that dot, repeat, join into a smooth curve, then add N → S arrows.
Drawn from real examiner reports.
Do not swap iron and steel properties
Candidates often reverse iron and steel. Correct: iron is a soft magnetic material — easily magnetised and demagnetised — used for electromagnet cores and induced magnets. Steel is a hard magnetic material — it retains its magnetism — used for permanent magnets. Remember the direction: soft = loses magnetism (iron); hard = keeps it (steel).
November 2023 Paper 31/32/33 Q10(a) and June 2023 Paper 32/33 Q7(a)(ii) — examiner reports explicitly note that "many candidates interchanged the properties of iron and steel".
Only repulsion proves magnetism
Attraction does not prove magnetism: an unmagnetised magnetic material becomes an induced magnet with the opposite pole at the near end, so it is attracted whichever pole is brought near. Only repulsion by a known magnet proves the specimen is itself a magnet — test both ends, and if any end is repelled it is a magnet.
June 2024 Paper 41/42/43 Q7(a) — examiner report explicitly states: "A common misconception was that there would be no force on an unmagnetised piece of steel" and "Candidates needed to state clearly that both ends need to be tested for repulsion or attraction."
Magnetic field: name force AND magnetic pole
"The region around a magnet" scores zero — it omits force and magnetic pole. The mark scheme needs two elements: (1) a region (2) in which a force acts on a magnetic pole (or a magnetic material experiences a force). Do not borrow the electric-field wording "a region in which a charge experiences a force".
June 2023 Paper 42 Q8(a)(i) — examiner report: "many candidates were unable to state what is meant by a magnetic field"; common errors named explicitly.
Field lines never cross or stop at a pole
Field lines never cross — two field directions at one point is impossible. They are closed loops: continue them through the magnet body (S → N inside); do not stop them at the pole surface, which implies the field ends there and loses the mark. Lines closer together mean a stronger field, so draw them densest at the poles, thinning out with distance.
Field direction: compass points N to S
The field direction at a point is the way the north-seeking end of a plotting compass points — from N to S outside the magnet. Wrong answers examiners flag: "towards the N pole", or borrowing the electric-field idea (direction of the force on a positive charge). State "from N to S", or "the direction of the force on a north pole".
Not all metals are magnetic
A common trap is assuming every metal is magnetic. Only iron, steel, nickel and cobalt are magnetic; copper, aluminium, brass and gold — and non-metals like wood and plastic — are not. Answering "metals" or "conductors" scores zero: Cambridge needs the named materials. Cobalt is the magnetic material candidates most often leave off the list.
Field-line sketch: shape, arrows, density
Markers give three separate marks: (1) correct shape; (2) an arrow on every line pointing N → S outside — one missing arrow loses it; (3) lines as closed loops, densest at the poles. Work in order: label poles, shape, arrows, density.
Give both elements of each definition
Write each definition with both elements: a magnetic field = a region where a force acts on a magnetic pole; a permanent magnet keeps its magnetism without an external field; an induced magnet magnetises in a field and loses it when the field is removed.
Comparisons: state both sides
For "compare iron and steel", give both properties, not one: "steel retains/keeps its magnetism; iron loses/does not retain it". A one-sided or vague answer like "steel is a better magnetic material" is not credited — the contrast must be explicit.
Magnetism test: repulsion, both ends
To show a specimen is magnetised, the key word is repulsion — only repulsion proves it, because an unmagnetised magnetic material is also attracted. Say you test both ends of the specimen against a known magnet; if any end is repelled, it is a magnet.
This topic has no numeric formulas. All marks come from precise language about definitions, field directions, and material properties. The mark-scheme vocabulary below replaces a formula table.
| Term | Cambridge mark-scheme definition (both elements required) |
|---|---|
| Magnetic field | A region in which a force acts on a magnetic pole (or on a magnetic material) |
| Permanent magnet | A magnet that (1) retains its magnetism (2) without an external magnetic field; made from a hard magnetic material (e.g. steel) |
| Induced magnet | A material that (1) becomes magnetised when placed in an external magnetic field and (2) loses most of its magnetism when the external field is removed; made from a soft magnetic material (e.g. iron) |
| Hard magnetic material | A material difficult to demagnetise — retains magnetism strongly (e.g. steel); used for permanent magnets |
| Soft magnetic material | A material easily magnetised and demagnetised (e.g. iron, nickel); used for electromagnet cores and induced magnets |
Define a magnetic field.
A student holds the north pole of a bar magnet near end P of an iron bar.
(a) State the name of the type of magnet that the iron bar becomes. [1]
(b) Explain why the iron bar is attracted to the bar magnet. [2]
(c) The student moves the bar magnet away from the iron bar. Describe what happens to the magnetism of the iron bar. [1]
