CIE iGCSE Co-ordinated Sciences-P4.1 Simple phenomena of magnetism- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P4.1 Simple phenomena of magnetism – Study Notes
CIE iGCSE Co-ordinated Sciences-P4.1 Simple phenomena of magnetism – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole) and south pole (S pole), attraction and repulsion, magnetised and unmagnetised
- State the differences between the properties of temporary magnets (made of soft iron) and the properties of permanent magnets (made of steel)
- State the difference between magnetic and non-magnetic materials
- Describe how a permanent magnet differs from an electromagnet
Supplement
- Describe a magnetic field as a region in which a magnetic pole experiences a force
- State that the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point
- Describe induced magnetism
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Magnetic Poles and Forces
Magnets have two poles — the north pole (N) and the south pole (S). The forces between poles and materials can be described using attraction and repulsion.
1. Forces Between Magnetic Poles
- Like poles repel: N–N or S–S → repulsion force.
- Unlike poles attract: N–S → attraction force.
- The force is strongest near the poles of the magnets.
2. Forces Between Magnets and Magnetic Materials
- Magnetic materials: iron, steel, cobalt, nickel.
- A magnet will always attract a magnetic material, regardless of whether it is near the N pole or S pole.
- This is because the material becomes induced magnetised — its domains align with the external magnetic field.
3. Magnetised vs Unmagnetised Materials
- Unmagnetised: Domains (tiny magnetic regions inside the material) are randomly oriented → no overall magnetism.
- Magnetised: Domains align in the same direction → material becomes a magnet with a clear N and S pole.
- Steel is a permanent magnet material (hard to magnetise, hard to demagnetise). Iron is a temporary magnet material (easy to magnetise, easy to lose magnetism).
| Situation | Force |
|---|---|
| N pole – N pole (like poles) | Repulsion |
| S pole – S pole (like poles) | Repulsion |
| N pole – S pole (unlike poles) | Attraction |
| Magnet – magnetic material (iron, steel, etc.) | Attraction only (due to induced magnetism) |
Example :
Why does a magnet always attract an iron nail, regardless of whether the nail is near its N pole or S pole?
▶️ Answer/Explanation
Step 1: The magnet’s field induces magnetism in the iron nail by aligning its domains.
Step 2: The end of the nail near the magnet becomes the opposite pole to the magnet’s pole.
Step 3: This results in attraction, regardless of which pole is used.
Final Answer: The magnet always attracts iron due to induced magnetism.
Temporary and Permanent Magnets
Different materials can be used to make magnets. Their properties depend on how easily they are magnetised and demagnetised.
1. Temporary Magnets (Soft Iron)
- Soft iron is magnetised very easily.
- It is also easily demagnetised when the magnetising force is removed.
- Produces a strong but temporary magnet.
- Uses: Electromagnets, transformer cores, motor cores → where magnetism must be switched on/off.
2. Permanent Magnets (Steel)
- Steel is harder to magnetise.
- It is hard to demagnetise, so it retains its magnetism for a long time.
- Produces a weaker but permanent magnet.
- Uses: Compass needles, fridge magnets, loudspeakers → where constant magnetism is required.
| Property | Temporary Magnet (Soft Iron) | Permanent Magnet (Steel) |
|---|---|---|
| Ease of Magnetisation | Easily magnetised | Hard to magnetise |
| Ease of Demagnetisation | Easily demagnetised | Hard to demagnetise |
| Strength | Strong but temporary magnetism | Weaker but permanent magnetism |
| Typical Uses | Electromagnets, transformer cores, motor cores | Compass, fridge magnets, loudspeakers |
Example :
Why is soft iron used in electromagnets instead of steel?
▶️ Answer/Explanation
Step 1: An electromagnet must be magnetised quickly when current flows and lose magnetism when current is switched off.
Step 2: Soft iron is easily magnetised and demagnetised, so it responds quickly.
Step 3: Steel would stay magnetised (permanent magnet), which is not suitable for electromagnets.
Final Answer: Soft iron is used because it is a temporary magnet that can be switched on and off easily.
Magnetic and Non-Magnetic Materials
1. Magnetic Materials:
- Can be attracted to magnets.
- Can be magnetised (temporary or permanent).
- Examples: iron, steel, nickel, cobalt.
2. Non-Magnetic Materials:
- Not attracted to magnets.
- Cannot be magnetised.
- Examples: copper, aluminium, plastic, wood.
Permanent Magnets vs Electromagnets
Permanent Magnet:
- Made of steel or other hard magnetic materials.
- Produces a constant magnetic field.
- Strength cannot be varied (fixed).
- Always magnetised (cannot be switched off).
- Uses: Compass needles, fridge magnets, loudspeakers.
Electromagnet:
- Made by passing a current through a coil wound around a soft iron core.
- Magnetic field exists only while current flows.
- Strength can be varied by changing current or number of turns.
- Can be switched on and off easily.
- Uses: Electric bells, relays, cranes for lifting scrap metal, MRI machines.
Example :
Why are electromagnets used in cranes for lifting scrap metal instead of permanent magnets?
▶️ Answer/Explanation
Step 1: A crane needs to pick up and release scrap metal easily.
Step 2: Electromagnets can be switched on (to attract) and off (to release), unlike permanent magnets.
Step 3: Their strength can also be varied by changing the current.
Final Answer: Electromagnets are used because they can be controlled and switched off when the load needs to be released.
Magnetic Field
A magnetic field is a region of space where a magnetic pole experiences a force.
Direction of a Magnetic Field:
- The direction of the magnetic field at a point is defined as the direction of the force that would act on a north pole placed at that point.
- By convention, magnetic field lines are drawn to show this direction.
- Field line convention: Field lines go out of the North pole of a magnet and into the South pole.
Key Features of Magnetic Field Lines:
- They never cross each other.
- The closer the lines, the stronger the field.
- The field is strongest near the poles of a magnet.
- Field lines form closed loops outside and inside the magnet.
| Concept | Explanation |
|---|---|
| Magnetic Field | Region where a magnetic pole experiences a force |
| Direction of Field | Direction of force on a north pole at that point |
| Field Line Convention | From North → South (outside the magnet) |
Example :
At a point near the north pole of a bar magnet, in which direction will a free north pole move?
▶️ Answer/Explanation
Step 1: By definition, magnetic field direction = direction of force on a north pole.
Step 2: A north pole is repelled by another north pole.
Final Answer: The free north pole will move away from the bar magnet’s north pole, following the field line direction.
Induced Magnetism
Induced magnetism occurs when a magnetic material (e.g. iron, steel, nickel, cobalt) becomes temporarily magnetised when placed in a magnetic field.
How It Happens:
- In an unmagnetised material, the atomic magnetic domains are randomly oriented → no overall magnetism.
- When placed near a magnet or in a magnetic field, the domains align with the field.
- This produces a temporary north and south pole in the material → it behaves like a magnet.
Key Features:
- Induced poles are always opposite to the nearby pole of the inducing magnet → causes attraction.
- This is why a magnet will always attract magnetic materials (never repel them).
- If the magnetising force is removed, the material often loses its magnetism (especially soft iron).
Examples of Induced Magnetism:
- An iron nail placed near a bar magnet becomes temporarily magnetised and is attracted to the magnet.
- Paper clips can form a chain when one is touched by a magnet, each becoming an induced magnet.
Example :
Why does a bar magnet always attract an iron nail, no matter which pole is used?
▶️ Answer/Explanation
Step 1: The magnet induces an opposite pole in the end of the iron nail closest to it.
Step 2: Opposite poles attract, so the nail is drawn toward the magnet.
Final Answer: The magnet always attracts the nail due to induced magnetism, regardless of which pole is used.