Magnetic Fields

All magnets produce a magnetic field: an area around the magnet where forces influence other magnets or magnetic materials.

Magnetic field lines always go from the north pole to the south pole. This is shown by the arrows, so make sure to include arrowheads as they show the direction of the field lines. Magnetic fields are strongest near the north and south poles, which is shown by the concentration of the lines.

The spacing between the field lines indicates the strength of the magnetic field.

  • The closer the field lines are, the stronger the magnetic field is – So the magnetic field lines are closer together at the poles.
  • The further the field lines are, the weaker the magnetic field is – So the magnetic field lines are slightly further apart as you go away from the magnets.

Finding Magnetic Fields

Two ways that magnetic field lines can be shown are by plotting compasses and by using iron fillings.

Plotting compasses

One method to show magnetic field lines is by using plotting compasses.

Here we have many small compasses surrounding the bar magnet. As you can see, the north pole of each compass points towards the south pole at all times. If you extend these indications, they will resemble the original magnetic field diagram, emerging from the north pole and entering the south pole.

Iron filings

Another method to visualize magnetic field lines is to place a bar magnet in a pile of iron fillings. The iron fillings will sort themselves along the magnetic field lines.

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.

Here we can see the field lines of the two magnets interacting. As we know that field lines travel from north to south, it is easier to understand why there is an attraction between opposite poles.

Like poles

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

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

This means that when like poles are placed together, there is a repulsion.

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