Drawing the shape
You cannot see a magnetic field. Field lines are a drawing of it. N and S mark the north and south poles of a magnet.
Step 1 of 3
- A bar magnet, labelled N and S. No lines yet.
- Field lines run from N to S outside, arrows shown.
- Wrong: two lines crossing. A real field never does this.
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The rule
Field lines are closed curves. Outside a magnet they run from N to S. Closer lines mean a stronger field. Two field lines never cross. A closed curve has no end. It comes back to where it started.
A field line is a curve. A small compass placed on it points along the line.
| Feature | What it means |
|---|---|
| An arrow on the line | The direction of the field there |
| Lines close together | A stronger field |
| Lines far apart | A weaker field |
| Lines never cross | A compass cannot point two ways at once |
Worked example
Look at a bar magnet's field lines. They are closest together near the poles. Closer lines mean a stronger field, so the field is strongest there. It is weaker far away, where the lines are farther apart.
Inside the magnet the lines run from S to N. So each line comes back to where it started.