Poles, Magnetic Fields and Magnetic Materials

Magnetism is one of the fundamental forces in nature and underpins a vast range of technologies — from electric motors and generators to MRI scanners and maglev trains. This lesson covers the basic ideas of magnetic poles, magnetic fields, and the materials that interact with magnets, all as required by the AQA GCSE Combined Science Trilogy specification (8464), Physics Paper 2, section 7.1.

Magnetic Poles

Every magnet has two poles — a north pole (N) and a south pole (S). These are the regions where the magnetic force is strongest.

The fundamental rule of magnetic poles:

Like poles repel — N repels N; S repels S.
Unlike poles attract — N attracts S; S attracts N.

If you cut a bar magnet in half, you do not get an isolated north pole and an isolated south pole. Instead, you get two smaller magnets, each with its own north and south pole. This means that magnetic monopoles (a single isolated pole) have never been observed.

graph LR
    subgraph "Attraction"
    A["N"] -->|"attract"| B["S"]
    end
    subgraph "Repulsion"
    C["N"] -->|"repel"| D["N"]
    end
    subgraph "Cut in half"
    E["N|S"] --> F["N|S  +  N|S"]
    end

Exam Tip (AQA 8464): A classic 1-mark question: "What happens when two north poles are placed near each other?" Answer: They repel. Always state whether the interaction is attraction or repulsion — do not just say "they push away."

Magnetic Fields

A magnetic field is the region around a magnet where a magnetic force acts on another magnetic material or on a moving charge. You cannot see a magnetic field, but you can represent it using field lines (also called lines of magnetic force).

Rules for Magnetic Field Lines

Field lines go from north to south outside the magnet (and from south to north inside the magnet).
Field lines never cross.
The closer together the field lines, the stronger the magnetic field.
Field lines are three-dimensional — they exist all around the magnet, not just in a flat plane.
The direction of the field at any point is the direction a north pole of a small compass needle would point.

Field Pattern of a Bar Magnet

graph TD
    subgraph "Bar Magnet Field (top view)"
    A["N pole"] -->|"field lines curve outward"| B["S pole"]
    A -->|"lines closest together at poles"| C["Strongest field near poles"]
    end

The field around a single bar magnet is shaped like an elongated set of loops:

Lines emerge from the north pole and curve around to enter the south pole.
The lines are closest together at the poles, showing the field is strongest there.
Far from the magnet, the lines spread out, showing the field gets weaker with distance.

Field Patterns for Two Magnets

Arrangement	Pattern	Key Feature
Two N poles facing each other	Lines repel; neutral point between them	There is a point of zero field (neutral point) exactly between the two poles
N pole facing S pole	Lines connect smoothly from N to S	The field between the magnets is approximately uniform (evenly spaced parallel lines) if they are close

Exam Tip: If you are asked to draw field lines between two magnets, always include arrows on the lines (pointing N to S) and make sure lines from like poles curve away from each other.

Magnetic and Non-Magnetic Materials

Only certain materials are strongly attracted to magnets. These are called magnetic materials.

Material	Magnetic?	Notes
Iron	Yes	Easily magnetised but loses magnetism easily (soft magnetic material)
Steel	Yes	Harder to magnetise but retains magnetism well (hard magnetic material)
Nickel	Yes	Magnetic, used in some alloys
Cobalt	Yes	Magnetic, used in strong permanent magnets
Copper	No	Not attracted to magnets
Aluminium	No	Not attracted to magnets
Wood / Plastic / Glass	No	Non-magnetic

Common GCSE Exam Mistake: Students often write that "all metals are magnetic." This is wrong — only iron, nickel, cobalt, and their alloys (such as steel) are magnetic. Most metals (copper, aluminium, gold, silver, zinc, etc.) are not magnetic.

Ferromagnetic Materials

The term ferromagnetic refers to materials that are strongly magnetic. The three ferromagnetic elements are iron, nickel, and cobalt. Steel is an alloy of iron and carbon, so it is also ferromagnetic.

Inside a ferromagnetic material, groups of atoms align their tiny magnetic fields in the same direction, forming regions called magnetic domains. In an unmagnetised piece of iron, the domains point in random directions and cancel out. When placed in a magnetic field, the domains align with the field, and the material becomes magnetised.

graph LR
    subgraph "Unmagnetised (domains random)"
    A["→"] --- B["↑"] --- C["←"] --- D["↓"] --- E["↗"]
    end
    subgraph "Magnetised (domains aligned)"
    F["→"] --- G["→"] --- H["→"] --- I["→"] --- J["→"]
    end

The Earth's Magnetic Field

The Earth behaves as though it has a giant bar magnet inside it. The geographic North Pole is near the magnetic south pole of this imaginary bar magnet (because the north pole of a compass needle points towards geographic north, and opposite poles attract).

Key facts:

The Earth's magnetic field is roughly uniform over small areas on the surface.
A plotting compass aligns with the Earth's field and points approximately north–south.
The Earth's magnetic field protects us from charged particles in the solar wind, deflecting them towards the poles (causing the aurora borealis and aurora australis).

Worked Example 1: Identifying Poles

A student places two bar magnets on a table. Magnet A has its north pole pointing right. Magnet B is placed to the right of Magnet A, and the two magnets repel. Which pole of Magnet B faces Magnet A?

Answer: Since the magnets repel, the facing poles must be like poles. Magnet A's north pole faces right, so Magnet B's north pole must face left (towards Magnet A). Like poles repel.

Worked Example 2: Comparing Field Strength

A student draws the magnetic field around a bar magnet. Near the north pole, the field lines are 2 mm apart. Near the middle of the magnet, the field lines are 8 mm apart. Where is the field stronger?

Answer: The field is stronger where the lines are closer together. The field lines are 2 mm apart near the north pole compared with 8 mm apart near the middle, so the field is stronger near the north pole — approximately 4 times stronger (since field strength is roughly proportional to line density).

Worked Example 3: Compass Needle Direction

A compass is placed at point X between two bar magnets arranged as follows: Magnet 1 has its N pole on the left; Magnet 2 (to the right of the compass) has its S pole facing left. In which direction does the compass needle point at X?

Answer: Field lines go from N to S outside the magnet. Magnet 1's N pole pushes field lines to the right; Magnet 2's S pole receives field lines from the left. Both effects point the field to the right at point X. The compass needle (which points in the direction of the field) therefore points to the right.

Summary Table

Concept	Key Detail
Magnetic poles	Every magnet has N and S; like poles repel, unlike attract
Magnetic field	Region where a magnetic force acts; represented by field lines (N → S)
Closer field lines	Stronger field
Magnetic materials	Iron, nickel, cobalt (and alloys like steel)
Non-magnetic metals	Copper, aluminium, gold, silver, zinc
Magnetic domains	Groups of aligned atoms; random in unmagnetised material, aligned in magnetised material
Earth's field	Behaves like a bar magnet; geographic N ≈ magnetic S

Exam-Style Practice

Explain why breaking a magnet in half does not produce an isolated north pole. (2 marks)
Draw the magnetic field pattern between two bar magnets placed with their north poles facing each other. Label the neutral point. (3 marks)
A student claims that aluminium is a magnetic material because it is a metal. Explain why this claim is incorrect. (2 marks)
Describe what happens to the magnetic domains in an iron nail when it is brought close to a bar magnet. (3 marks)