νµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτ ψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπα σδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκ χϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθ

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1 θωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψ υιοπασδφγηϕκλζξχϖβνµθωερτψυιοπασδ φγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζ ξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµ Magnetism θωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψ Mr R Gopie υιοπασδφγηϕκτψυιοπασδφγηϕκλζξχϖβν µθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτ ψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπα σδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκ λζξχϖβνµθωερτψυιοπασδφγηϕκλζξχϖβ νµθωερτψυιοπασδφγηϕκλζξχϖβνµθωερτ ψυιοπασδφγηϕκλζξχϖβνµθωερτψυιοπα σδφγηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκ λζξχϖβνµρτψυιοπασδφγηϕκλζξχϖβνµθ ωερτψυιοπασδφγηϕκλζξχϖβνµθωερτψυι οπασδφγηϕκλζξχϖβνµθωερτψυιοπασδφγ ηϕκλζξχϖβνµθωερτψυιοπασδφγηϕκλζξ χϖβνµθωερτψυιοπασδφγηϕκλζξχϖβνµθ

2 Magnetism Non- magnetic materials These cannot be made into magnets and are not affected (in terms of attraction/repulsion) by magnets. Examples include wood copper, concrete, aluminium, plastic (generally non- metals) Magnetic Materials These can be made into magnets and are attracted to magnets through magnetic induction. Examples include the elements iron (Fe), cobalt (Co), and Nickle (Ni) and certain materials containing one or more of these elements these elements are magnetic and are said to be ferromagnetic- other examples include alloys such as alcomax, ticonal, alnico, magnadur etc. Magnetically Hard Materials are those that are difficult to magnetize and difficult to demagnetize. They include materials such as steel, alcomax, alnico and magnadur. Such materials are good for making permanent magnets which are used as magnets and are used in d.c. motors and moving- coil meters (such as ammeters and voltmeters) Magnetically soft Materials are those that are easy to magnetize and easy to demagnetize. They include materials such as iron. Such materials are good for making temporary magnets that can be formed as electromagnets (and used as lifting magnets, in electric bells, in a.c motors in magnetic relays and in transformers). Such materials are also used as keepers (to keep pairs of bar magnets in such a way that their magnetic fields do not interact with external fields. This protects the bar magnets). They can also be used as shields (which can screen or protect certain devices from the effects of magnetic fields) Consider a comparison between the magnetic properties of a typical magnetically soft material, such as iron, and a typically magnetically hard material such as steel. 2

3 Iron Easy to magnetize and easy to demagnetize Has a higher magnetic saturation (i.e. can be magnetized to a greater extent and thus become a stronger magnet- under the same circumstances) Steel Difficult to magnetize and difficult to demagnetize Has a lower magnetic saturation Theories of magnetism One theory of magnetism suggests that all materials are made up of tiny magnets arranged haphazardly in all directions. In magnetic materials these tiny magnets can be made to align themselves along a particular line. So a specimen of material can acquire magnetic poles and so become a magnet. However in a non- magnetic material this is not possible the tiny magnets remain haphazardly arranged Another theory suggest that materials are made up of domains each of which contains a collection of tiny magnets which are all aligned the same way. The various domains are associated with various lines 3

4 in a non- magnetic material and an un- magnetized magnetic material. However, in a magnetized magnetic material, i.e. a magnet the tiny magnets in the various domains become aligned the same way (or mostly so at least). Magnets Magnets have no effect (in terms of attraction/repulsion) on non- magnetic materials but can attract magnetic materials which are un- magnetized through the process of magnetic induction Magnets can repel other magnets and this repulsion is the test for a magnet. Magnets exist in a variety of sizes and shapes, and these include bar magnets, u- shaped magnets, ring magnets, cylindrical magnets and disc magnets. Bar magnets usually have their magnetism concentrated at the ends of the bar and the regions of concentration of magnetism are called the poles of the magnet. There are two types of poles a north pole and a south pole. Amagnet with two such poles is referred to as a dipole magnet or bipolar magnet. 4

5 Like poles repel one another and unlike poles attract one another one another. The magnitude of the force (F) of attraction or repulsion varies approximately inversely with the distance (d) between the poles i.e. F 1/d. Methods for making magnets (i.e magnetization) include 1) single touch 2) Divided touch 3) An electrical method This involves the use of a long, extended coil (i.e. solenoid) carrying d.c. (and aligned in a N- S line). Methods of demagnetization include 1) Rough Handling (pounding) 2) Heating 3) An electrical method involving the use of a solenoid carrying a.c. (and aligned in a E- W line). 5