4.1.3Electricity and Magnetism
Magnetic Fields — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 10 parts Lesson 7 of 65 1 quiz
Lesson summary
4.1.3 Magnetic Fields — IGCSE PHYSICS notes: Define a magnetic field, describe field lines and patterns and what they show about strength.Definition — a region in which a magnetic pole experiences a forceVector field — it has a size and a direction at every pointDirection — the d…
- Compass needle
- Meaning of the arrow
- Never cross
- Closed loops
- Strongest at the poles
- Weaker with distance
Section 1 of 10What a magnetic field is
Definition
- Definition a region in which a magnetic pole experiences a force
Vector field
- Vector field it has a size and a direction at every point
Direction
- Direction the direction of the force on a north pole placed at that point
Compass needle
- Compass needle a tiny magnet that turns to point along the field
Section 2 of 10Field lines
Direction
- Direction field lines go from the north pole of a magnet to the south pole, with an arrow on each line
Meaning of the arrow
- Meaning of the arrow the direction in which the magnetic force would act
Never cross
- Never cross the field has only one direction at each point
Closed loops
- Closed loops outside the magnet lines run from north to south and inside from south to north
Section 3 of 10Strength of the field
Strongest at the poles
- Strongest at the poles field lines are closer together at the ends of the magnet
Weaker with distance
- Weaker with distance field lines get further apart as the distance from the magnet increases
Strong or weak
- Strong or weak closely spaced lines show a strong field and widely spaced lines a weak field
Force
- Force a small magnet or iron feels the biggest force near the poles
Section 4 of 10Field patterns
| Arrangement | Pattern |
|---|---|
| Bar magnet | Lines curve from the north pole to the south pole, close together near the poles |
| Unlike poles facing | Lines run from north to south across the gap, nearly parallel and evenly spaced between flat faces |
| Like poles facing | Lines bend away and a neutral point between them has zero field |
| Attracting and repelling magnets | Field lines show the interaction between the two magnets |
- Uniform field
- parallel, evenly spaced lines mean the same strength and direction everywhere
Section 5 of 10Earth's magnetic field
Pattern
- Pattern the Earth's field is like that of a bar magnet, with a magnetic pole near each geographic pole
Compass
- Compass points to geographic north because the magnetic pole there is magnetically a south pole
Section 6 of 10Drawing a field
Direction
- Direction add arrows pointing away from the north pole and towards the south pole
Strength
- Strength draw lines further apart as the distance from the magnet increases
Spacing
- Spacing draw lines closer together at the poles
Section 7 of 10Shielding
Field through materials
- Field through materials a magnetic field passes through most materials such as air, glass and plastic
Soft iron shield
- Soft iron shield field lines prefer to pass through a soft iron ring or box, so the space inside is almost free of field
Use
- Use protects sensitive instruments and watches from stray fields
Section 8 of 10More from the specification
1Field line density and magnetic forces
- Field line density and magnetic forces closer magnetic field lines indicate stronger local magnetic forces acting perpendicular to moving charges.
2Magnetic field mapping
- The magnetic field around permanent bar magnets and solenoids is mapped using iron filings or plotting compasses, with field lines pointing from North to South.
3Induced magnetism in ferromagnetic materials
- Placing unmagnetised iron or steel in a magnetic field causes alignment of magnetic domains, creating induced magnetic polarity.
4Electromagnets and core materials
- A current-carrying solenoid produces a magnetic field amplified by inserting a magnetically soft iron core that easily magnetises and demagnetises.
5Plotting compass field mapping
- Plotting compass field mapping small compass needles align tangent to local magnetic field lines, pointing from north to south.
6Electromagnets versus permanent magnets
- Electromagnets versus permanent magnets electromagnets produce magnetic fields only when current flows,
- whereas permanent steel magnets maintain magnetization.
7Magnetic induction in metals
- Magnetic induction in metals unmagnetised ferromagnetic metals like iron or nickel develop induced opposite poles when placed in external fields.
8Electromagnet
- Magnet made by current through a coil around a magnetic core.
9Permanent magnet
- Magnet whose field is always there.
10Induced magnetism
- Magnetism produced in a magnetic material by a nearby magnet
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Magnetic field | Region in which a magnetic pole experiences a force |
| Field line | Line showing the direction of the force on a north pole |
| Uniform field | Field with parallel, evenly spaced lines of constant strength |
| Neutral point | Point where the fields of two magnets cancel and the field is zero |
| Magnetic shield | Soft iron container that keeps a space almost free of magnetic field |
Section 10 of 10Exam technique
1
Drawing field lines with no arrows — each line needs a direction arrow.
2
Drawing field lines that cross or touch — they never cross.
3
Saying the field is strongest where lines are far apart — it is strongest where they are closest.
4
Saying the compass points to a north magnetic pole of the Earth — it points to a magnetic south pole near geographic north.
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