A magnetic field is the area around a magnet where the magnetic force works. It is stronger at the poles of the magnet. Magnetic objects placed within a magnetic field would be affected in two ways: a magnetic material would always be attracted to the magnet, whereas another magnet could be attracted or repelled.
A magnetic field can be shown when placing small shavings of iron - iron filings - near a magnet. They arrange themselves in such a way that they show the magnetic field (see diagram below). Each iron filing becomes a small magnet and is attracted more strongly to the poles of the magnet.
A magnetic field can also be shown by drawing magnetic field lines. These lines would be shown by the iron filings as they line up along the field lines. The direction of the magnetic field is the same as the direction of the lines and the less space between the lines, the stronger the magnetic field. Different types of magnets produce different arrangements of magnetic field lines.
The diagram below shows an example of magnetic field lines, the Earth’s magnetic field, as the Earth acts as a giant bar magnet:
The Earth behaves as if it has large permanent magnet at its centre; that’s why a compass always points North. It is attracted to the Earth’s geographical North pole, which is the Earth’s South magnetic pole.
The Earth’s magnetic field protects us from cosmic rays and solar wind, making life on Earth possible. The Earth’s centre has a dense fluid outer core and a solid inner core, both of which are high in iron-rich materials. The magnetic field is created due to a combination of the movement of molten iron in the outer core and the convection currents caused by the heat of the inner core. This is the Geodynamo Theory. Aurora Borealis (the Northern Lights) are charged particles from the Sun attracted by the Earth’s magnetic poles. The Earth’s magnetic field extends into space and forms the magnetosphere.