Magnetism - Part I

Magnets have been known to human being for more than two to three thousand years. Magnets are substances that attract some other substances and are generally made up of iron. Nickel also shows magnetic behavior sometimes. Alloys of Fe-Ni and few other elements added to them show magnetism. Some rare earth elements also show high magnetism. Alloys of Sm-Co are used as permanent magnets in many laboratories.  

Magnets attract materials like Fe, Ni, Co. These materials are called magnetic materials. Some materials like copper, aluminum, gold, tin are not attracted to magnets; these materials are called non-magnetic materials. We will try and see in this chapter, what underlying properties make some substances magnetic and others non-magnetic.

What we will study in this chapter 
1. Characteristics of a magnet (magnetic pole, field and lines of force)
2. Electricity and magnetism
3. Theory of magnetism
4. Earthís magnetic field

Characteristics of a magnet (magnetic pole, field and lines of force)
Naturally occurring iron ores called loadstones are magnetic. They are used to make artificial magnets with convenient shapes and sizes for use. Shapes of  magnets can vary as - a disc, a bar magnet or a horse shoe magnet.  

Magnets are associated with a pair of poles : the north pole and the south pole. If you hang a bar magnet freely, it will come to rest with its north pole facing the geographical north. If you try and displace it, again it will rotate and align itself to the geographical north.  The compass needle is also made up of a magnet and it is widely used to find directions especially by navigators.  

Properties of magnets
We have seen earlier that a magnet has two poles. A north pole and a south pole. All the properties of magnets arise because of their poles. (The properties can be explained by the theory of magnetism later in the chapter).

• If you bring two magnets close to each other, you will observe that like poles repel each other and unlike poles attract each other. Also the poles exist only at the free ends of the magnet.

• If you bring iron filings or iron nails close to a magnet, the filings or nails will get attracted to the magnetic poles. The centre of the magnet does not attract the filings or the nails.

• If you break up a magnet, you will see, new north and south poles form immediately. A magnetic pole cannot be isolated.  

• If you spread iron filings around a magnet, they will align themselves along the lines in a curved fashion, starting from one pole and ending on the next pole. These lines are called lines of force of the magnet.
  

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