Natural magnets are composed of the substances created by nature, which have the property of attraction. The earth itself is considered to be the biggest natural magnet. Some other natural magnets are iron ore, magnetite and other iron-pyrites, etc. These magnets are composed of iron and oxygen and also have the property of attracting iron filings.
The force of these natural magnets cannot be increased or decreased as per one's wish or requirement. It remains the same always. Therefore, the use of the natural magnets is very restricted.
The man-made magnets are known as artificial magnets. The force of the artificial magnets can be increased or decreased at different degrees and can be manufactured in various designs. The artificial magnets can again be divided into two main categories: Electromagnets and Permanent magnets.
Electromagnets- The electromagnets work when electricity is applied to them and without electricity they have no power of their own to act. These magnets are extremely strong as they are composed by placing a metal core inside a coil of wire carrying an electric current. Electromagnets are most useful when a magnet must be switched on and off. The ideal example is the large cranes used to lift cables and rods in construction.
Permanent Magnets - The permanent magnets remain permanently magnetised once they are charged with electric current and can be used without electricity applied to them every time they are put to use. The permanent magnets do not lose their magnetism if they are properly preserved with keepers attached to them for many years. These magnets are usually composed of ferromagnetic material that comprises of atoms and molecules that each have a magnetic field and are positioned to reinforce each other. An everyday example is the magnet on refrigerator which is used to hold notes on a refrigerator door.
Permanent magnets are further classified into four types based on their composition including 'Neodymium Iron Boron', 'Samarium Cobalt', 'Alnico' and 'Ceramic' or 'Ferrite'.
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