Magnetic Fields

Around a magnet, there are invisible magnetic field lines that indicate the magnetic field.

The image illustrates a "Bar magnet" with its magnetic field lines. At the centre is a horizontal bar magnet divided into two equal parts. The left side is coloured red and labelled "N" representing the north pole, while the right side is coloured blue and labelled "S" for the south pole. Surrounding the magnet are concentric curved lines, representing the magnetic field lines, that emerge from the north pole and curve around to enter the south pole. These lines depict the flow of the magnetic field and are accompanied by arrows, indicating the direction from the north pole towards the south pole.

These magnetic field lines always come out of the north pole and go towards the south pole. This is shown by the direction of the arrows.

Make sure to include arrowheads, as they indicate the direction of the field lines. The magnetic fields are strongest at the north and south poles, which is shown by the line concentration.

The distances between the field lines show how strong the magnetic field is.

  • The closer the field lines are, the stronger the magnetic field is – which is why the magnetic field lines are closer together at the poles
  • The further the field lines are, the weaker the magnetic field is – which is why the magnetic field lines are slightly further apart as you move away from the poles

Finding Magnetic Fields

Two ways that magnetic field lines can be shown are:

  • Plotting compasses
  • Iron fillings

Plotting compasses

Using plotting compasses is one way to visualise magnetic field lines.

A horizontal bar magnet in the centre, split into two sections: the left half is coloured red and labelled "N" for north, while the right half is blue and labelled "S" for south. Scattered around the magnet are seven compasses, each with a wooden rim. Every compass has a red-tipped needle pointing towards the "N" of the bar magnet and a blue-tipped end pointing towards the "S", showcasing the magnet's influence on the compass needles.

Here we have many small compasses surrounding the bar magnet. As you can see, the north pole is pointing towards the south pole at all times. If you extend the lines, they will start to resemble the original magnetic field diagram, extending from the north pole and leading to the south pole.

Iron filings

Another way to show magnetic field lines is by placing a bar magnet in a pile of iron filings. The iron fillings will sort themselves along the magnetic field lines.

The image depicts a red vertical bar magnet in the centre, surrounded by a dense field of iron filings that have arranged themselves in response to the magnet's magnetic field. The iron filings create a radiating pattern, highlighting the magnetic field lines emanating from and returning to the magnet.

Here we can see the iron fillings showing the magnetic field around the bar magnet.

Magnetic Field Lines of Attraction

Opposite poles

We can use the magnetic field lines of two magnets to show how opposite poles attract.

The image illustrates two adjacent bar magnets with opposing poles facing each other, specifically the south pole of the left magnet facing the north pole of the right magnet. Around the magnets are depicted magnetic field lines, shown as concentric circles with arrows. The field lines emerge from the magnets, indicating the direction and strength of the magnetic field. The overlapping field between the two magnets is denser, highlighting the interaction and attraction between opposite poles. The overall visual representation demonstrates the magnetic force interaction when two bar magnets with opposing poles are brought close to each other.

In this scenario, you can observe the field lines of the two magnets interacting. As we know that field lines travel from north to south, it is easy to see why there is an attraction between opposite poles.

Like poles

Now let’s look at like poles. For example, two north poles placed next to each other.

The image depicts two adjacent bar magnets with like poles facing each other: the south pole of the left magnet faces the south pole of the right magnet and vice versa for the north poles. Surrounding the magnets are magnetic field lines represented as concentric circles with arrows. These field lines demonstrate the direction and strength of the magnetic field, with the arrows between the magnets pointing away from each other. This visual representation showcases the repulsive force and interaction when two bar magnets with similar poles are positioned close to each other.

As the magnetic field lines are trying to go from north to south, the magnets will repel each other. The magnetic field lines of the magnets are not touching because the magnetic field lines are trying to reach the south pole.

This means that when like poles are positioned near each other, they repel each other.