Explain how iron filings can be used to show the shape of a magnetic field around a bar magnet, and describe what the pattern of iron filings tells us about the strength of the field in different regions.

Iron filings are small ferromagnetic particles that become magnetised in the presence of a magnetic field. When sprinkled over a bar magnet they align themselves along the field lines, forming a visible pattern that shows the shape of the field.

The pattern reveals the field’s geometry: lines emerge from the north pole, curve around the magnet and re‑enter at the south pole.

Where the filings are closest together – i.e. where the density of filings is greatest – the magnetic field is strongest. This occurs near the poles, where the filings are most densely packed.

Where the filings are more spread out, the field is weaker, as the spacing between filings increases with distance from the poles.