Induced Magnetism — 3D Simulation
A bar magnet (red N / blue S) sits to the left of a transparent iron or steel bar. As you drag the magnet closer, magnetic domains inside the bar rotate and align with the external field — the near face develops an induced opposite pole, the far face develops the same pole as the magnet. Field lines show the complete closed flux circuit: gap arcs between the poles, internal B-field through the bar, and large return loops sweeping around the outside. The magnet’s own field is always visible as white arcs. Switching to hard steel demonstrates retained magnetism after the magnet is withdrawn.
Class Activity — “Predict, Observe, Explain” (Year 10/11, ~20 min)
Setup: Students work in pairs, one on the sim.
- Predict (2 min) — Before touching anything: “If I bring a N pole toward the iron bar, what pole appears on the near face? What happens to the domains?” Students write answers on a mini-whiteboard.
- Observe (5 min) — Drag the magnet in slowly. Toggle Labels on. Students check their prediction against the teaching panel and induction chip.
- Flip & re-predict (3 min) — “Now flip the magnet so S faces the bar. What changes?” Predict, then test.
- Steel vs iron (5 min) — Bring the magnet close, then switch to Hard Steel and pull it away. “What do the field lines show now? Why does soft iron demagnetise but steel doesn’t?”
- Exit question (5 min, written) — “A steel paper clip is held near a bar magnet. Explain, using the word ‘domain’, why the clip is attracted rather than repelled.”
Key AQA points covered: induced poles always opposite · attraction explained by opposite poles · soft iron = temporary, steel = permanent · domain alignment as the microscopic mechanism.