The ancient Greeks discovered that certain kinds of stones attract pieces of iron with a force that is called "magnetic". The Chinese may have discovered this even earlier. Magnetic stones contain iron or other magnetic metals such as nickel and cobalt. The fact that iron and a few other metals can have the property of attracting or repelling each other is called magnetism. It turns out that a piece of iron may be magnetized. If the magnetized iron is in the shape of a long, thin rectangular solid, it is called a bar magnet.
DefinitionBack to Top
Bar magnet is a kind of magnetic material in a shape of the long rectangular solid. Two ends of the bar magnet is north and south pole respectively. The magnetic field direction of a bar magnet is from north pole to the south pole.
Magnetic FieldBack to Top
If two bar magnets are placed near to each other end to end, then these magnets either attract or repel each other. If they attract each other we can realize that the two poles are opposite. If the same poles are placed near to each other these magnets get repelled. The two ends or poles of a bar magnet are known as the north pole and south pole. If there is a force on a magnet at some point in space, we say that a magnetic field exists at that point in space. A magnetic field is a vector field whose direction outside the magnet is defined to be away from a north pole and towards a south pole.
Neodymium Bar MagnetsBack to Top
Permanent magnets made from a mixture of iron and a substance known as neodymium can produce extremely strong magnetic forces. In fact, some versions of neodymium magnets the size of a 50-cent coin can lift a 10kg object. Neodymium magnets can also retain their magnetism for long periods of time. It's a kind of flat and round type magnet usually magnetized at their flat surfaces.
Strong Bar MagnetBack to Top
We have already noted that the pattern of magnetic field lines of a bar magnet is similar to the pattern of electric field lines near two electric charges. The unit of magnetic field can be denoted in Tesla (T). The magnetic field close to one of the poles of a strong bar magnet has a magnitude of about 1T. The Earth also acts approximately as a bar magnet, with a magnetic field of approximately 50$\mu$T near the Earth surface.