Magnetic field lines

Magnets create magnetic fields. These magnetic fields cannot be seen. They fill the space around a magnet where the magnetic forces work, and where they can attract or repel magnetic materials.

Finding magnetic fields

Field lines around a bar magnet
Field lines around a bar magnet

Although we cannot see magnetic fields, we can detect them using iron filings. The tiny pieces of iron line up in a magnetic field.

Drawing magnetic field diagrams

It would be difficult to draw the results from the sort of experiment seen in the photograph, so we draw simple magnetic field lines instead.

A bar magnet, with several curved lines pointing from the north to south poleA bar magnet, with several curved lines pointing from the north to south pole

In the diagram, note that:

  • the field lines have arrows on them
  • the field lines come out of N (north pole) and go into S (south pole)
  • the field lines are more concentrated at the poles

The magnetic field is strongest at the poles, where the field lines are most concentrated.

Two bar magnets

The magnetic field pattern when two magnets are used is shown in this diagram.

A: Single  magnet, field lines curve, N to S. B: Unlike pole attraction - field lines N of magnet travel to S of second magnet. C: Like pole repulsion - N of two bar magnets, field lines forced apart.Magnetic field lines for fields involving two magnets

Note the different patterns seen when two like poles are used and two opposing poles are used.

Uniform magnetic field

When magnetic field lines are the same distance apart from each other, we say that the magnetic field is uniform. This is shown in the diagram:

Two bar magnets lie side by side. One is labelled north and the other south. Magnetic field lines travel in straight lines from the north to the south magnet, at right angles to both magnets.Magnetic field lines in a uniform field
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