Magnets and Magnetism

Making a magnet
If a steel rod is stroked 15-20 times with one end of a bar magnet, the domains within the rod can be made to line up so that they are all pointing in the same direction. The rod is then magnetized.
Magnetic fields
When an object made of iron or steel is placed close to a magnet, it is attracted towards it. This happens because the object is inside the magnet’s magnetic field.
Discovering the shape of a magnetic field
1. Using iron filings
A piece of paper is placed over the magnet. Iron filings are gently sprinkled over the paper. The pattern formed by the filings shows the shape of the magnetic field.
2. Using a compass
A magnet is placed on top of a piece of paper and drawn around. A compass is placed next to the magnet, a circle drawn around it and the direction of the compass needle marked inside the circle. The compass is then moved so that its tail is next to the compass point just drawn. A circle is again drawn around the compass and its direction recorded. This process is repeated all over the paper. The compass needles on the paper will show the shape and direction of the magnetic field.
Magnetic field pattern around a bar magnet
Both methods show that the field pattern around a bar magnet is as given in figure 11Where the field is strong, the lines are drawn close together. Where the field is weak, the lines are drawn well apart.
The earth’s magnetic field
If a bar magnet is suspended so that it is free to rotate, it will eventually come to rest with its north pole pointing northwards and its south pole pointing south wards. The magnet is therefore behaving like a simple compass. Magnets and compasses do this because they are inside the earth’s magnetic field.
It is this magnetic field which has allowed travelers to navigate using a compass.