er poles are called consequent poles. A magnet can have zero poles, two poles, four poles, six poles and so on. This pattern shows that the number of poles is always even, this is because poles always exist in pairs. The lifting power of a magnet does not depend on the number of poles, however, but the shape of the polar surface, the shape of the load to be lifted and the type of iron used in the load. The material used for permanent magnets has to process high retentivity and high coercivity. Retentivity is the ability of the material to retain much of its magnetism after the magnetizing force is removed. Coercivity is the power of resisting demagnetization. Every bar and horseshoe magnet tends to demagnetize itself to a certain extent. Magnets can be made by several different means. The prosess of making an unmagnetized object magnetized is called magnetic induction. The most powerful magnets are made by placing a bar of metal inside a coil of wire and then passing an electric current through the wire. This requires enormous currents of electricity; the more electricity used, the more magnetism surrounding the wire. You might wonder how long it takes before a magnet cant become any further magnetized or if there even is such a point. The truth is there is a point at which this happens. It is said to be magnetically saturated which happens when the magnetism of all of its domains has been aligned parallel to the external field. At this time no further increase in magnetization can take place, no matter how much the external field is increased. Another method of making magnets is by using particles of iron. The particles have to be less than .000002 centimeters in diameter. This makes it so that each particle is small enough to be a domain. If the single domain particles are magnetized in the direction of their elongation, the shaped powders become magnetically stable. The manufacturing process consists of aligning the f...
