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What are magnetic poles and fields, and how do magnetic materials behave?

Describe magnetic poles and fields, the laws of magnetic force, and magnetic and non-magnetic materials

A focused answer to the O-Level Physics outcome on magnetism. Magnetic poles, the law of force between poles, magnetic field lines and how to plot them, magnetic versus non-magnetic materials, and magnetic induction.

Generated by Claude Opus 4.87 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
  4. Try this

What this dot point is asking

SEAB wants you to describe magnetic poles and the law of force between them, to draw and plot magnetic field patterns, to tell magnetic from non-magnetic materials, and to understand magnetic induction. The big idea is that a magnet has two poles, produces a field in the space around it, and that field exerts forces and can induce magnetism in nearby magnetic materials.

The answer

Magnetic poles

Every magnet has two poles, a north pole and a south pole. They cannot be separated: break a magnet in half and each piece has its own north and south pole. The law of magnetic force is:

like poles repel,unlike poles attract\text{like poles repel}, \qquad \text{unlike poles attract}

A freely suspended magnet turns so its north pole points toward the Earth's geographic north, which is the basis of the compass.

Magnetic materials

  • Magnetic (ferromagnetic) materials are attracted to magnets and can be magnetised: iron, steel, nickel, and cobalt.
  • Non-magnetic materials are not attracted: copper, aluminium, wood, plastic, and most other materials.

Soft iron is easily magnetised and demagnetised, so it is used for temporary magnets (such as electromagnet cores). Steel keeps its magnetism, so it is used for permanent magnets.

Magnetic fields and field lines

A magnetic field is the region around a magnet where a magnetic force acts. It is represented by field lines that:

  • point from the north pole to the south pole outside the magnet,
  • never cross,
  • are closer together where the field is stronger (near the poles).

You can plot the field with a plotting compass, marking the direction the needle points at many places and joining the dots into smooth lines from north to south.

Magnetic induction

When a magnetic material is placed in a magnetic field, it becomes a magnet itself, with an induced pole. The end nearest the magnet's north pole becomes an induced south pole, so the two attract. This is why a magnet can pick up a chain of paper clips: each clip becomes an induced magnet.

Examples in context

Example 1. The compass and the Earth. The Earth behaves like a giant bar magnet, and a compass needle is a small magnet free to turn. Its north pole lines up with the Earth's magnetic field, pointing roughly toward geographic north, which is how navigators have found direction for centuries.

Example 2. Fridge magnets and steel doors. A fridge magnet sticks to the steel door because the door is a magnetic material. The magnet induces an opposite pole in the steel, and the resulting attraction holds the magnet (and your notes) in place, while it would not stick to an aluminium or plastic surface.

Try this

Q1. State what happens when the north pole of one magnet is brought near the north pole of another. [1 mark]

  • Cue. They repel, because like poles repel.

Q2. Name two magnetic materials and one non-magnetic material. [2 marks]

  • Cue. Magnetic: iron and steel (or nickel, cobalt). Non-magnetic: copper (or aluminium, plastic, wood).

Q3. Explain why a magnet can attract an unmagnetised steel nail. [2 marks]

  • Cue. The magnet induces an opposite pole in the nail; the unlike poles then attract, pulling the nail to the magnet.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original4 marks(a) State the law of magnetic force between two poles. (b) Two bar magnets are placed end to end and attract each other. State what this tells you about the two poles facing each other, and explain.
Show worked answer →

(a) Like poles repel and unlike poles attract.

(b) The two poles facing each other must be unlike (one north and one south), because they attract. If they were like poles (both north or both south) they would repel instead.

Markers reward the law (like repel, unlike attract), and the deduction that attraction means the facing poles are unlike (a north and a south).

Original4 marks(a) Describe how you would plot the magnetic field pattern around a bar magnet using a plotting compass. (b) State two features that the field lines show about the magnetic field.
Show worked answer →

(a) Place the bar magnet on paper. Put a plotting compass near one pole, mark dots at the two ends of the needle, move the compass so the tail sits where the head was, and repeat to trace a line from north to south. Repeat from different starting points to build the whole pattern.

(b) The field lines show the direction of the field (from north to south, given by the way a compass needle points) and the strength of the field (lines are closer together where the field is stronger, such as near the poles).

Markers reward a valid plotting-compass method tracing lines from north to south, and the two features: direction (north to south) and strength (closeness of the lines).

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