Nature of Magnetisms
Magnets are found in a natural state in the form of a magnetic ore with two main types – Magnetite and Lodestone. These two magnets are highly effective and if they are suspended from a piece of string then they take their position with the Earth's magnetic field pointing towards North. For example, we can refer to the needle of compass. In practical applications these natural magnets are disregarded as their magnetism is very low and man-made magnets are of more magnetic strengths.
Magnetism is of two types - “Permanent Magnets” and “Temporary Magnets”. There are different types of materials which make magnets like iron, nickel, nickel alloys, chromium and cobalt. When mixed or alloyed together with other materials like iron or aluminium peroxide they become strong magnets like “alcomax”, “hycomax”, “alni” and “alnico”. In the non-,agnetic state magnetic material is in the form of loose magnetic chains or individual tiny magnets. The overall effect of this type of arrangement results in zero or very weak magnetism. As soon as the material is magnetised the arrangement of the molecules change and the become “lined-up” in such a way that they can produce magnetic arrangement in a series. This idea is known as Weber's Theory.
Magnetic Molecule Alignment of a Piece of Iron and a Magnet
Weber's theory is based on the fact that all atoms have magnetic properties due to the spinning action of the atoms electrons. Magnetic materials are composed of groups of tiny magnets at a molecular level around the atoms. A magnetised material has its tiny magnets lined up in one direction only. A material which has molecular magnets directing at several directions will have its magnets neutralised by the neighbouring magnet. So the magnetic effect will also be neutralised.
Any magnetic material produces a magnetic field and it depends on the alignment of the magnetic domains. The effect of applying a magnetising force to the material is to align some of the domains to produce a non-zero magnetisation value. If the force is removed then the magnetism decays with time and when it is retained this power is called Retentivity.
Magnetic Flux
All magnets have two regions called magnetic poles, Lines of flux are collectively referred as magnetic field of the magnet. At each end of a magnet is a pole with highest magnetism. These lines of flux cannot be seen by the naked eye but through iron fillings onto a sheet of paper or by a small compass to trace them out. The two poles are North Pole and South Pole. Magnetic fields are shown as lines of force which go to make up a magnetic field and they are called Lines of Force or Magnetic Flux.
Lines of Force from a Bar Magnets Magnetic Field
The magnet field remains strongest near to the poles. Moreover the magnetic lines form closed loops and the magnetic poles are always in pairs. Magnetic flux doesn't flow from the north to the south pole as it is a static region around a magnet consisting of magnetic force. Magnetic forces attract and repel like electric forces and when two lines of force are brought close together the interaction causes attraction and repulse. This effect leads to the concept that “opposites attract”.
Magnetic Field of Like and Unlike Poles
When magnetic field lines are plotted with a compass the lines of force are produced in such a way to give a definite pole at each end of the magnet. Magnetism can be destroyed by heating or hammering the magnetic material, but cannot be destroyed into two pieces. So if you are to use magnetism in electrical or electronic calculations, it is necessary to define what are the various aspects of magnetism. Now we know that the lines of force or more commonly the magnetic flux around a magnetic material is given the Greek symbol, Phi, ( Φ ) with the unit of flux being the Weber, ( Wb ) after Wilhelm Eduard Weber.
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