Magnetic Fields — Magnetism & Electromagnetism | IGCSE Physics

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 9% of your exam marks.

stable

Medium

Stable9%

Magnetic field patterns, the motor effect and Fleming's Left-Hand Rule tested in most series.

What a magnetic field is

A magnetic field is the region around a magnet in which a force would act on another magnet, or on a piece of magnetic material placed within it
Magnetic fields are visualised using magnetic field lines:
- The direction of the field at any point is the direction the north pole of a small test compass would point if placed at that point
- The strength of the field is shown by the spacing of the lines: close together where the field is strong, far apart where it is weak
Two important drawing rules:
- Field lines always run from N to S outside the magnet (and from S to N inside it, completing a closed loop)
- Field lines never cross or touch each other; they only meet at the poles themselves

Exam tip

Drawing magnetic field lines around a bar magnet

What comes up: draw or complete the field-line pattern around a bar magnet, or add arrowheads to given lines.

Write (two marks): (1) Lines run from the north pole and curve round to enter the south pole — arrowheads point from N to S on every line. (2) Lines are closest together at the poles (where the field is strongest) and spread out further away; no two lines cross or touch.

Watch out: if any arrowhead points the wrong way (S to N outside the magnet), the direction mark is lost entirely. Check every arrow on every line before moving on.

The field around a bar magnet

The field is strongest at the poles, so the lines are packed close together there and spread out further from the magnet
The pattern is symmetric: lines bow outward from the N pole, curve round, and re-enter the S pole

A bar magnet with the conventional N–S field-line pattern drawn around it, showing close-together lines at the poles and spreading lines further out, plus two additional small panels showing the line pattern between two attracting (N–S) and two repelling (N–N) bar magnets

Uniform fields

A uniform magnetic field has the same strength and the same direction at every point. On a diagram it is drawn as a set of equally spaced parallel field lines
A uniform field can be made by placing two flat magnets with opposite poles facing each other, separated by a few centimetres. Between the poles, the field looks uniform to a good approximation; outside that gap it is curved like a normal two-magnet field