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| Sunday, 15 January 2006 |
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Junior Observer |  |
| News Business Features Editorial
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Amazing magnets In our day-to-day life, magnets come in handy in many ways. From simple chores to advanced industrial works, magnets are helpful in our lives. What is a magnet? What are the types of magnets and how do they work? Let's take a closer look at these amazing magnets. A magnet is any object that has a magnetic field. It attracts ferrous objects (containing iron) like pieces of iron, steel, nickel and cobalt. In the early days, the Greeks observed that the naturally occurring 'lodestone' attracted iron pieces. From that day began the journey into the discovery of magnets. These days, magnets are made artificially in various shapes and sizes, depending on their use. One of the most common magnets - the bar magnet - is a long, rectangular bar of uniform cross-section, that attracts pieces of ferrous objects. The magnetic compass needle is also commonly used. The compass needle is a tiny magnet, which is free to move horizontally on a pivot. One end of the compass needle points to the North direction and the other end points to the South. The end of a freely pivoted magnet will always point in the North-South direction. The end of a magnet that points to the North is called the North Pole and the end that points South is called the South Pole. It has been proven by experiments that like magnetic poles in different magnets (e.g. North - North) repel each other, whereas unlike poles (North - South) attract each other. What is a magnetic field? The space surrounding a magnet, in which magnetic force is exerted, is called a magnetic field. If a bar magnet is placed in such a field, it will experience magnetic forces. However, the field will continue to exist even if the magnet is removed. The direction of magnetic field at a point is the direction of the resultant force acting on a hypothetical (supposed, but not necessarily true) North Pole placed at that point. How is a magnetic field created? When current flows in a wire, a magnetic field is created around the wire. From this it has been decided that magnetic fields are produced by the motion of electrical charges. A magnetic field of a bar magnet thus results from the motion of negatively charged electrons in the magnet. Magnetic lines of force Just as an electric field is described by drawing the electric lines of force, a magnetic field is described by drawing the magnetic lines of force. When a small North magnetic pole is placed in the magnetic field created by a magnet, it will experience a force. And if the North Pole is free, it will move under the influence of the magnetic field. The path traced by a North magnetic pole free to move under the influence of a magnetic field is called a magnetic line of force. In other words, the magnetic lines of force are the lines drawn in a magnetic field along which a North magnetic pole would move. The direction of a magnetic line of force at any point gives the direction of the magnetic force on a North Pole placed at that point. Since the direction of a magnetic line of force is the direction of force on a North Pole, the magnetic lines of force always begin on the N-pole of a magnet and end on the S-pole. A small magnetic compass, when moved along a line of force, always sets itself along the line next to it. So, a line drawn from the South Pole of the compass to its North Pole indicates the direction of the magnetic field. Properties of the magnetic lines of force 1) The magnetic lines of force originate from the North Pole of a magnet and end at its South Pole. 2) The lines come closer to one another near the poles of a magnet, but they are widely separated at other places. 3) They do not intersect (or cross) one another. 4) When a magnetic compass is placed at different points on a magnetic line of force, it aligns itself along the tangent (straight line which touches the outside of a curve without dividing it) to the line of force at that point. These are just some of the basic concepts of magnetism. One cannot possibly grasp the depth and appreciate the versatility of magnets without reading more about the uses of magnets, and electromagnetism, among other things. Types of magnets There are various types of magnets depending on their properties. Some of the most well known are listed below. Permanent magnets These are the most common type of magnets that we know and interact with, in our daily lives, e.g. the magnets on our refrigerators. These magnets are permanent in the sense that once they have been magnetised, they retain a certain degree of magnetism. Permanent magnets are generally made of ferromagnetic material. Such material consists of atoms and molecules that each have a magnetic field and are positioned to reinforce (strengthen) each other. Permanent magnets can further be classified into four types, based on their composition: 1. Neodymium Iron Boron (NdFeB or NIB) 2. Samarium Cobalt (SmCo) 3. Alnico 4. Ceramic or Ferrite NIB and SmCo are the strongest types of magnets and are very difficult to demagnetise. They are also known as rare earth magnets since their compounds come from the rare earth or Lathanoid series of elements in the periodic table. The 1970s and 80s saw the development of these magnets. Alnico is a compound made of ALuminium, NIckel and CObalt. Alnico magnets are commonly used and first became popular around the 1940s. They are not as strong as NIB and SmCo and can be easily demagnetised. This magnet is however, least affected by temperature. This is also the reason why bar and horseshoe magnets have to be taken care of, to prevent them from losing their magnetic properties. Ceramic or Ferrite magnets are the most popular today. They were first developed in the 1960s. These are fairly strong magnets, but their magnetic strength varies greatly with variations in temperature. Permanent magnets can also be classified into Injection moulded and Flexible magnets. Permanent magnets can be demagnetised in the following ways: Heating a magnet until it is red hot Stroking one magnet with another in a random fashion; or Hammering or jarring will loosen the magnet's atoms from their magnetic attraction. Temporary magnets Temporary magnets are those that simply act like permanent magnets when they are within a strong magnetic field. Unlike permanent magnets however, they loose their magnetism when the field disappears. Paperclips, iron nails and other similar items are examples of temporary magnets. Temporary magnets are used in telephones and electric motors. Electromagnets Had it not been for electromagnets, we would have been deprived of many luxuries and necessities in life, including computers, television and telephones. Electromagnets are extremely strong. They are produced by placing a metal core (usually an iron alloy) inside a coil of wire carrying an electric current. The electricity in the current produces a magnetic field. The strength of the magnet is directly proportional to the strength of the current and the number of coils of wire. Its polarity depends on the direction of current flow. While the current flows, the core behaves like a magnet. However, as soon as the current stops, the core is demagnetised. Electromagnets are most useful when a magnet must be switched on and off, as in large cranes used to lift cables and rods in the construction industry. Superconductors are the strongest magnets. They don't need a metal core at all, but are made of coils of wire made
from special metal alloys, which become superconductors when cooled to
very low temperatures. |
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