Contents
The study of Physics Topics involves the exploration of matter, energy, and the forces that govern the universe.
How Magnets were Discovered and Explain Poles of a Magnet
A magnet is an object which attracts things made of iron, steel, nickel and cobalt. Figure shows a magnet attracting a paper clip made of steel due to which the paper clip sticks to it. Magnets are made of iron, steel or other alloys of iron by the process of magnetisation. Magnets made in this way are called artificial magnets (which means man-made magnets).
Magnets are made in different shapes and sizes so that they can be used for different purposes. One of the most common shapes is the bar magnet. A bar magnet is a long rectangular magnetised bar of iron or steel (see Figure). Some of the other types of magnets are horseshoe magnet, U-shaped magnet, cylindrical magnet (or rod magnet), button magnet and ring magnet (see Figure).
There is an old story that magnets were discovered by chance by an old shepherd named Magnes who lived in ancient Greece. Magnes used to take his herd of sheep and goats to a nearby mountain for grazing. He always took a wooden stick with him to manage his herd of sheep and goats.
The wooden stick had an iron casing at its lower end. One day, Magnes suddenly felt that something was pulling his stick away from him. It appeared as if the iron covered end of stick was being attracted by a rock and got stuck to the rock (see Figure).
Magnes had to pull hard to free the iron end of stick from the rock. Actually, the rock was a natural magnet which attracted the iron end of Magnes’ stick. This rock which behaved like a magnet was given the name ‘magnetite’.
Magnetite rock contains iron. Magnets were named so after the name of shepherd Magnes. Some people, however, believe that the natural magnet called magnetite was first discovered at a place called Magnesia in Turkey.
The magnetite rock had wonderful properties : The magnetite attracted pieces of iron towards itself. And when a thin strip of magnetite was suspended from a thread so that it could rotate freely, the magnetite strip always aligned itself in the same direction (north-south direction). One end of the freely suspended magnetite strip always pointed towards the north direction.
Due to this property, the freely suspended mangetite strips were used by sailors in the ships to find directions in olden times (because they always pointed in the north direction). Since magnetite was used to find directions to lead the way for ships, it was also called ‘lode stone’ (which means leading stone’). The pieces of magnetite rock are known as natural magnets (see Figure). We will now discuss magnetic and non-magnetic materials.
Magnetic Materials and Non-Magnetic Materials
Activity
Let us keep an iron nail, paper clip, brass screw, aluminium foil, plastic comb, coin, sewing needle, piece of paper and copper wire on a wooden table. Bring a bar magnet near each one of these objects. We will see that iron nail, paper clip, and sewing needle are attracted by the magnet and hence stick to the magnet.
All these objects like nail, paper clip and sewing needle which are attracted by a magnet are made of iron (or steel). Thus, iron is a material which is attracted by a magnet. Steel (which is an alloy of iron) is also attracted by a magnet. The objects like brass screw, aluminium foil, plastic comb, coin, piece of paper and copper wire are not attracted by the magnet. So, they do not stick to the magnet.
From the above activity we conclude that some materials or objects are attracted by a magnet whereas other materials or objects are not attracted by a magnet. So, on the basis of their behaviour towards a magnet, all the materials can be divided into two groups : magnetic materials (which are attracted by a magnet) and non-magnetic materials (which are not attracted by a magnet). Let us study the magnetic and non-magnetic materials in somewhat detail.
Those materials which are attracted by a magnet are called magnetic materials. Iron, steel, nickel and cobalt are attracted by a magnet, so iron, steel, nickel and cobalt are magnetic materials. The most common and important magnetic materials are, however, iron and steel.
The objects made of iron and steel like nails, paper clips, sewing needle, hair pins, paper pins, drawing pins, safety pins, knife blade, scissors, spade, blade, etc., are all attracted by a magnet. So, all these objects made of iron and steel are also magnetic objects. We know that steel is an alloy of iron metal. This means that iron is the common metal in all the ordinary objects which are attracted by magnets.
Similarly, the objects made of nickel and cobalt metals are also attracted by magnets and hence they are also magnetic in nature. Please note that magnetic materials can be magnetised which means that magnetic materials can be converted into magnets. In fact, magnets are usually made from magnetic materials such as iron and steel.
Those materials which are not attracted by a magnet are called non-magnetic materials. All the materials other than iron, steel, nickel and cobalt are non-magnetic materials. For example, wood, plastic, rubber, paper, cloth, glass, leather, thermocol, copper, aluminium, brass, lead, stone, diamond, graphite, paint, charcoal, air, water, skin and bones, etc., are all non-magnetic materials (because they are not attracted by a magnet).
In fact, most of materials around us are non-magnetic materials. The objects made of non-magnetic materials are also non-magnetic in nature. Thus, a wooden spoon, a plastic scale, pencil, rubber eraser, copper wire, aluminium can, brass utensils, a book, leather shoes, and wood shavings, etc., are all non-magnetic objects. Please note that non-magnetic materials cannot be magnetised. This means that non-magnetic materials cannot be converted into magnets.
The magnetic and non-magnetic properties of various objects are made use of in our day to day life. This will become clear from the following examples.
(i) If a large number of pins from a pin box fall on the floor and get scattered, we can collect all the pins quickly by using a magnet (instead of picking up each and every pin by hand). So, if we move a magnet over the pins scattered on the floor, all the pins (being magnetic) will get attracted to the magnet and stick to it. We can then remove these pins from the magnet and put them back in the box.
(ii) Suppose a carpenter has mixed some iron nails and screws with lots of wood shavings while working. We can help him in getting back the nails and screws from the wood shavings by using a magnet. If we move a magnet through the wood shavings containing nails and screws, then the nails and screws (being magnetic) will get attracted to the magnet and stick to it. Wood shavings are non-magnetic and hence they do not stick to the magnet.
It is a common observation that a pencil sharpner gets attracted by a magnet though its body is made of a non-magnetic material called plastic. Actually, there is also a steel blade in the middle of sharpner. It is due to the presence of a steel blade (which is magnetic) in the middle of a sharpner that it is attracted by a magnet. From this discussion we conclude that magnets attract only magnetic materials. Magnets do not attract non-magnetic materials.
The Pull (or Attraction) of Magnets Can Pass Through Non-Magnetic Materials (Including Air)
The pull (or attraction) of magnets can pass through non¬magnetic materials like plastic, paper, cardboard, wooden plank, air, paint, skin and bone, etc. The fact that the pull or attraction of a magnet can pass through plastic (or paper) and air can be demonstrated by an interesting activity as follows.
Activity
Take a plastic cup (or paper cup) and fix it on a wooden stand with the help of a clamp as shown in Figure.
Place a magnet inside the plastic cup and cover it with a plastic lid. Take a short piece of thread and tie its one end to a paper clip of steel. The other end of thread is tied to a nail fixed on the base of the wooden stand exactly below the plastic cup.
Now, hold the paper clip in your hand and bring it up to a little distance below the bottom of the plastic cup containing magnet and then release the paper clip. We will see that the paper clip remains hanging in air like a kite a little distance below the plastic cup without any support (see Figure).
This happens because the force of pull (or attraction) exerted by ”the magnet kept inside the plastic cup passes through the plastic bottom of the cup as well as through the air below the cup and holds the paper clip. Please note that the length of thread used in this activity should be such that, when stretched, it keeps the paper clip a little distance below the plastic cup.
If, however, a longer length of thread is tied to the paper clip, then the paper clip will stick to the bottom of the plastic cup. This activity shows that the pull (or attraction) of a magnet passes through non-magnetic materials like plastic and air.
The pull (or attraction) of a magnet, however, cannot pass through magnetic materials like iron and steel objects. Before we go further and describe the poles of a magnet, we should know the term ‘iron filings’. Iron filings are the small particles of iron metal.
Poles of a Magnet
If a bar magnet is put into a heap of iron filings, then the iron filings will cling to it or stick to it. The maximum amount of iron filings cling to the two ends of the bar magnet (see Figure).
This shows that the force of attraction of the magnet is the strongest near the two ends of the bar magnet. The two ends of the bar magnet are called poles of the magnet. Poles are the places on the magnet where pull of the magnet (or attraction of the magnet) is the strongest.
We can now say that: The regions of a magnet where the attraction of magnet is the strongest are called poles of the magnet. A magnet has always two poles (whatever its shape may be). The two poles of a magnet are near its free ends (see Figure). The two poles of a magnet are always different. One pole of the magnet is called north pole and the other pole of magnet is called south pole.
The ‘North’ pole of a magnet is represented by writing the letter ‘N’ near its one end. And the ‘South’ pole of a magnet is represented by writing the letter ‘S’ near its other end (see Figure). The north pole and south pole of a magnet always exist together. Every magnet, whether big or small, has a north pole and a south pole. It is impossible to have a magnet having only one pole.
Please note that though the maximum amount of iron filings stick on the two ends (or two poles) of the bar magnet, some iron filings also stick to the middle part of the bar magnet (see Figure). This shows that some force of attraction also exists in the middle part of the bar magnet but it is very small.
We can use a magnet to find out whether the soil or sand at a place contains particles that have iron. This can be done as follows : Rub a magnet in the soil or sand and shake it gently to remove the particles of soil or sand from its surface. If some particles still remain sticking to the poles of the magnet, then this soil or sand contains particles that have iron. We will now discuss the meaning of ‘like poles’ and ‘unlike poles’.
(i) The same type of magnetic poles are called like poles. For example, a ‘North pole’ and another ‘North pole’ are like poles. Similarly, a ‘South pole’ and another ‘South pole’ are also like poles. In other words, N and N poles are like poles. Similarly, S and S poles are like poles. As we will study after a while, like magnetic poles repel each other.
(ii) The different types of magnetic poles are called unlike poles. For example, a ‘North pole’ and a ‘South pole’ are unlike poles (because they are different types of poles). We can also say that N pole and S pole are unlike poles. As we will study after a while, unlike magnetic poles attract each other.