Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised
4.1 Simple Phenomena of Magnetism
Learning Objective (AO1)
Describe the forces between magnetic poles and between magnets and magnetic materials, using the exact terminology required by the Cambridge IGCSE 0625 syllabus:
- North pole (N‑pole)
- South pole (S‑pole)
- Attraction
- Repulsion
- Magnetised
- Un‑magnetised
Glossary (AO1 Vocabulary)
North pole (N‑pole) – the end of a permanent magnet that points toward the Earth’s geographic north.
South pole (S‑pole) – the opposite end of a permanent magnet; it points toward the geographic south.
Attraction – a force that pulls two objects toward each other.
Repulsion – a force that pushes two objects apart.
Magnetised – a material that has acquired a magnetic field (its magnetic domains are aligned).
Un‑magnetised – a material that has no net magnetic field (its domains are randomly oriented).
1. Forces Between Magnetic Poles
- Like poles (N–N or S–S) → Repulsion
- Unlike poles (N–S) → Attraction
These rules are qualitative only; no formula is required for the IGCSE.
Quick‑check: What will happen if you bring the north pole of one magnet close to the south pole of another magnet? Answer: they will attract each other.
Magnetic Field (definition)
Magnetic field: the region around a magnet in which a north‑pole test charge would experience a force. The direction of the field at any point is the direction of the force that would act on a north pole placed at that point.
Field‑line pattern and direction (Core requirement)
Field lines emerge from the N‑pole, travel through the surrounding space, and re‑enter at the S‑pole. Inside the magnet the lines run from S to N, completing a closed loop.
2. Forces Between Magnets and Magnetic Materials
Induced Magnetism (syllabus wording)
When an un‑magnetised ferromagnetic material (e.g., iron) is placed in the magnetic field of a permanent magnet, the magnetic domains inside the material rotate so that they line up with the external field. The material therefore becomes magnetised and is attracted to the nearest pole, whether N or S.
Types of magnetic response
| Material Type | Magnetic Behaviour | Typical Examples |
|---|---|---|
| Ferromagnetic | Strong attraction; becomes magnetised (induced magnetism) | Iron, nickel, cobalt |
| Paramagnetic | Weak attraction | Aluminium, oxygen, platinum |
| Diamagnetic | Weak repulsion | Bismuth, copper, graphite |
| Non‑magnetic (practically negligible) | No noticeable force | Wood, plastic, most non‑ferrous metals (e.g., brass) |
Practical Demonstrations
- Bring a small iron nail close to either pole of a bar magnet. The nail is attracted to both poles because it becomes magnetised in the field.
- Place a compass near a magnet. The needle aligns with the field lines, pointing toward the magnet’s N‑pole.
- Use a piece of aluminium or copper near a strong magnet. Observe the very slight attraction (paramagnetic) or repulsion (diamagnetic).
Note: The effect is so weak it may require a strong magnet or a sensitive balance to detect.
3. Temporary (Soft‑Iron) vs Permanent Magnets
- Permanent magnet – retains its magnetisation without any external influence (e.g., a fridge magnet, a steel bar magnet).
- Temporary (soft‑iron) magnet – becomes magnetised only while an external magnetic field is present and loses its magnetisation as soon as the field is removed (e.g., the iron core of an electromagnet when the current is switched off).
Simple experiment – observing loss of magnetisation
- Place a soft‑iron rod between the poles of a strong permanent magnet. The rod is attracted and sticks to the magnet.
- Carefully remove the permanent magnet while keeping the rod isolated.
- After a few seconds the rod no longer attracts the magnet – it has become un‑magnetised again.
4. Drawing Magnetic Field Lines (Core requirement)
Students must be able to draw and interpret the pattern and direction of magnetic field lines around a bar magnet.
Step‑by‑step activity
- Lay a sheet of white paper on a flat surface.
- Place a bar magnet underneath the centre of the paper (or tape it to the underside of a clear plastic sheet).
- Sprinkle a thin layer of iron filings evenly over the paper.
- Gently tap the paper to allow the filings to settle along the field lines.
- Observe the pattern: lines emerge from the N‑pole, curve around the magnet, and re‑enter at the S‑pole. Inside the magnet the lines run from S to N.
- Using a pencil, trace the visible pattern. Indicate the direction of the field with arrows pointing away from the N‑pole and toward the S‑pole.
5. Real‑World Uses of Permanent Magnets and Electromagnets
- Fridge door seal – a permanent magnet holds the door shut; the field is constant and does not require power.
- Loudspeaker coil – an electromagnet (temporary magnet) is created when an audio signal passes through the coil, causing the attached diaphragm to vibrate.
- Magnetic levitation (maglev) train – powerful permanent magnets on the train interact with the track’s magnetic field to produce lift and propulsion without contact.
- Electric motor – a rotating coil becomes a temporary magnet when current flows, interacting with permanent magnets to produce motion.
6. Summary of Interactions
| Interaction | Resulting Force | Typical Materials |
|---|---|---|
| North pole – North pole | Repulsion | Two permanent magnets |
| South pole – South pole | Repulsion | Two permanent magnets |
| North pole – South pole | Attraction | Two permanent magnets |
| Magnet – Ferromagnetic material (un‑magnetised) | Strong attraction (material becomes magnetised) | Iron, nickel, cobalt |
| Magnet – Paramagnetic material | Weak attraction | Aluminium, oxygen |
| Magnet – Diamagnetic material | Weak repulsion | Bismuth, copper |
| Magnet – Non‑magnetic material | Negligible force | Wood, plastic, most non‑ferrous metals |
Common Misconceptions (Addressed)
- “Magnetism only works between two magnets.” – Ferromagnetic materials become magnetised in a magnetic field and are attracted.
- “North and south are fixed labels on any object.” – Only a magnet has permanent poles; an un‑magnetised piece of iron has no permanent poles.
- “All metals are attracted to magnets.” – Only ferromagnetic metals show strong attraction; others are weakly attracted, repelled, or essentially unaffected.