O-Level and SEC G3 Physics K323
P17: Magnetism
Represent magnetic fields, poles, materials, and force effects with field direction kept explicit.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Magnetism covers pole behaviour, induced magnetism, temporary and permanent magnets, compass use and field patterns around single and paired bar magnets.
Magnetic properties
A freely suspended magnet aligns approximately north-south. Like poles repel and unlike poles attract. Magnetic poles occur in pairs in the school model; cutting a bar magnet produces smaller magnets, not isolated poles.
Magnetic materials can be magnetised by a nearby field. Attraction alone does not prove that an object is a permanent magnet because induced magnetism can attract an initially unmagnetised magnetic material.
Temporary and permanent magnets
Soft iron magnetises strongly and loses magnetism readily, so it suits temporary electromagnets. Steel is harder to magnetise but retains magnetism, so it suits permanent magnets.
Choose a material from the required behaviour rather than memorising a material-use pair. A relay core needs rapid magnetisation and demagnetisation, while a compass needle needs retained magnetism.
Field direction and patterns
A magnetic field is represented by the direction in which the north-seeking pole of a small compass points. Outside a bar magnet, field lines run from north to south and are closer where the field is stronger.
Between unlike poles, lines connect across the gap. Between like poles, the fields oppose and curve apart, with a weak or neutral region between them depending on geometry. Field lines show a model, not physical threads.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: Why is soft iron used as the core of an electromagnet rather than steel?
- The core must become strongly magnetised when current flows.
- It must also lose most magnetism when current stops.
- Soft iron has high temporary magnetic response and low retention compared with steel.
Answer: Soft iron supports strong, controllable temporary magnetism.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Draw magnetic field direction from north to south outside a magnet and recognise field strength by line spacing.
- Distinguish magnetic materials, permanent magnets, and induced magnetism.
- Predict attraction or repulsion from pole and field information rather than diagram appearance.
Official outcome coverage
K323 P17: 5 mapped outcomes, references P17(a), P17(b), P17(c), P17(d), P17(e). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Map a field with a plotting compass, record direction at multiple points, and avoid treating drawn field lines as physical objects.
Exam traps and retrieval check
Avoid these traps
- Using attraction as the only test for a permanent magnet.
- Drawing external field arrows from south to north.
- Choosing steel for a core that must demagnetise quickly.
Check from memory
What is the sure magnetic test?
Repulsion between known like poles, because attraction can arise by induction.
How does a compass show field direction?
Its north-seeking end points along the field.
Where is a drawn field stronger?
Where field lines are closer together.
Pure versus Combined scope
Combined Physics revisits part of this core under CP15 Magnetism and Electromagnetism, but with reduced outcome scope. Combined students should follow the component checklist rather than assume every K323 outcome is assessable.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.