Magnets are objects that can exert a powerful force on other objects without touching them. A magnet can cause metal objects or other magnets to move from far away. There are many different kinds of magnets, from the simple refrigerator magnet all the way up to industrial magnets that can lift a car. Magnets are used in compasses to determine direction, in speakers to produce sound, in computers and televisions, and they have many other applications. Some magnets are formed naturally; others are made by humans.
Magnetism and Natural Magnets
All matter is made out of atoms. An atom can be thought of as a small nucleus of material around which orbit even smaller particles of matter called electrons. The electrons have an electrical charge, so when they orbit they form small loops of electrical current around each nucleus. Magnetic fields are formed by electricity. In most materials the little magnets formed by each atom are all pointing in different directions, and so they cancel each other out. In some materials such as lodestone, an iron ore, the Earth's magnetic field lined up all the atom-magnets and left the whole stone one large magnet.
People have used naturally occurring magnets for thousands of years. Once people found that other materials could also be made into magnets, they started producing stronger magnets by a variety of different processes. Certain metals can be made into magnets by exposing them to magnetic fields. Although just placing the metal in a magnetic field can work, making it vibrate increases the effect. Stroking the metal with the magnet also increases the effect. Heating the metal up while it is in the field and hammering it while it cools increases the effect even further. Steel and iron make good magnets. So does an alloy of aluminum, nickel, and cobalt called alnico.
Ceramic, Flexible, and Shaped Magnets
Ceramic magnets are made from iron oxide and barium or strontium carbonate. They are shaped and baked like any other ceramic. Flexible and shaped magnets are made by mixing magnetized powder (like iron oxide powder) in with resin or plastic. The resin or plastic can then be molded as normal, and the result is a magnet with a unique shape that can be flexible.
Electromagnets are unlike other kinds of magnets. They do not necessarily utilize any magnetic material in their construction. Because any moving electric current produces a magnetic field, a magnet can be made out of a battery and a wire. If the wire is formed in a loop, it creates a magnetic field with a north and south pole like permanent magnets. If many coils of wire are made of the same wire, then the magnet that is formed is even stronger. If iron or some similarly magnetizable material is put in the center of the coil, then the magnet becomes stronger still.
Superconducting magnets are a special type of electromagnet. The loops of wire are cooled to nearly absolute zero and disconnected from their power source. Because the coil is so cold the atoms in it are so still that they offer no resistance to the movement of the electrons, and the current keeps flowing. This results in a much stronger magnetic field being formed.
- compass image by cico from Fotolia.com