Magnetism

Salam (May God Bless You). Magnets are popular for many uses and are most important for making various infrastructure or complex circuits. Magnets are also used in the labs for various testing. Did you knew that magnets were first discovered thousands of years ago when people noticed a certain rock named lodestone having a very unusual property. If the rock was left hanging from a rope or placed on water, it would always point to the same direction. At the time no one had the idea that the rock actually had a magnetic property in it.

The reason it did this was because it always pointed towards the magnetic North Pole. This feature was then used as a compass which aided travellers when they couldn’t take bearings from the stars and the Sun. This rock is now known as magnetite and it is a well-known permanent magnet. Other permanent magnet materials are iron, steel, cobalt and nickel, etc. Materials which are attracted to a magnet such as these are known as magnetic, while the other materials are non-magnetic which are aluminium, copper and brass.

Properties of magnets

Magnets have their properties because of the magnetic field which surrounds a magnet. If drawing a diagram , the magnetic field is shown by the field lines and the stronger the magnetic field the more concentration of field lines there will be. The field lines always come from the North pole of a magnet, and to the south pole of the magnet. The picture other than the magnet you see is a solenoid which will be discussed later in this article.

To know why there is such a magnetic field, we should consider that there are tiny magnetic molecules or tiny magnets in a simple material such as iron which are unaligned. When magnetized, the tiny magnets will become more aligned such that it will be directed towards the North pole of the magnet. This causes the formation of magnets.

Some materials, when magnetised, retain its magnetism for a long time which is why these are called permanent magnets. These materials are named “hard” for this reason. Other materials remain magnetised for a very short amount of time which is why they are called “soft”.

The other properties to discuss is the law of magnetic poles. Every one knows that if two same poles are placed in front of each other, they repel each other off while putting the opposite poles of two magnets in front of each other causes the two magnets to be attracted to each other. This is also useful for finding out whether a material is a magnet or not. If you place two objects together with the same poles facing each other, one a magnet and other a magnetic material, if these two repel each other this means the magnetic material is a magnet.

The reason behind this is that the field lines come out of the North pole while it is taken in by the South pole, causing the two to be attracted while if you place two south poles, field lines are deflected and a null point is formed in the center.

Another property of a magnet is that when a magnetic object attached itself to the permanent magnet, the object becomes a magnet itself and attracts other magnetic objects towards it. This situation is called a magnetic induction. For example if you place a horseshoe magnet over a bunch of steel paper clips, the same effect will take place.

Magnetising

There are three ways for magnetising. One method is to use a single touch method. In this method, we stroke a straight iron bar with a magnet several times. If the North pole is used, the side that is first touched by the magnet then it will become the North pole while the other side will become the South pole. 

The second way is the double touch method. We use two magnets for this. On an iron bar, stroke a magnet from the center of the iron bar to the end using the south pole, while stroke the other end from the center to the opposite direction using the North pole. This will cause the iron bar to take the opposite polarity that the pole used to stroke it.

The last method is to use a coil of wire called a solenoid. Place an iron strip in the solenoid and pass the current. The current forms a magnetic field around the wire causing the tiny magnets in the iron bar to align and form a magnet. To find the North pole of the newly formed magnet, place your right hand on the solenoid and curl your fingers as such that the fingers point towards the direction of current. The direction the thumb points is where the North pole is.

Demagnetising

If you heat a permanent magnet or hit it by a hammer several times, it will lose its magnetism. This is because the tiny magnets gain kinetic energy due to these actions and vibrate vigorously, causing them to lose their alignment. Another way is that if we again put the magnet in a solenoid and pass on an alternating current (a.c), and slowly remove the current, the magnet will lose its magnetism.

Magnetic field around a current and a coil

If you pass a current through a wire, it will produce a magnetic field around it. The direction of the field depends upon the direction of the current itself. If the current moves downwards then the magnetic field is clockwise and if it moves upwards, the magnetic field is always anticlockwise. A fact to note is that when a solenoid has a current passing through it, the solenoid will have the same magnetic field as a bar magnet. When a wire moves around in a circle through a cardboard, there will be two magnetic fields formed. The first will move anticlockwise and the other clockwise.