- Pins in a pin holder do not fall even when it is held upside down. Why is this so ?
- While we are shutting the door of a fridge, we find that it closes automatically from a certain distance and does not open unless pulled again. Why is this so?
A magnet is used in these gadgets. A magnet is fitted in the cap of a pin holder and in the door of a fridge. Iron objects stick to a magnet.
What is a magnet ?
The material to which objects made from iron, nickel, cobalt, etc. get attracted is called a ‘magnet’. This property of a material is called ‘magnetism’.
- Take a magnet from the laboratory and bring it near various objects in your use. Which of them stick to the magnet ? What material is each of them made of ? Observe these things carefully. Classify the objects into two groups : those which stick to the magnet and those which do not.
- Take a mixture of sand, pieces of paper, sawdust, iron filings and pins in a saucer and pass a magnet around the mixture. What do you see ?
The materials that stick to a magnet are called magnetic materials, while those that do not stick to a magnet are called non-magnetic materials. The metals iron, cobalt, nickel are magnetic materials.
In the past…
There is a legend about the discovery of magnets. It is said that a shepherd named Magnes lived in Greece. Once, while his sheep were grazing, he sat down on a big rock. But, what a surprise he got when he tried to get up! His staff and his shoes were stuck to the rock. He had to use great force to pull himself away from the rock.
He realized that what had happened was because of the iron ferrule on his staff and the iron nails in his shoes. However, other rocks did not stick to his shoes or staff. Later, he showed the rock to everybody. The rock was named magnetite after Magnes, the shepherd. Magnetite is a natural magnet. It is also possible that the name ‘magnet’ came from Magnesia, the part of Greece where magnets were discoverd.
It was known quite long ago to the people in China and Europe that a piece of magnetite, hung freely, always settled in the north-south direction. These rocks then came to be used for finding the directions while travelling through unknown regions. That is why, they are also called lodestones (leading stones). This led to the invention of the mariner’s compass. Magnets can have a variety of shapes depending upon their uses. Today, magnets are used in many machines and gadgets or devices. They are all man-made magnets. Find out where the magnets shown in the pictures below are used.
Bar magnets, disc magnets, horseshoe magnets, ring-shaped magnets, cylindrical magnets as also small button magnets are the different shapes of magnets in everyday use.
When a magnet attracts an object, that object is displaced due to the magnetic force. In places like factories, ports, garbage depots, large objects are shifted from place to place. For this purpose, cranes with magnets are used. Work is done by magnetic force. This shows that magnetism is a kind of energy
Characteristics of a magnet
- Determine the directions in the class or laboratory. Tie a thread to the centre of a bar magnet and hang it from a stand. Note the direction in which the magnet settles and turn it around again. Let it settle and note the direction. Do this many times.
What do you observe ?
A magnet always settles in the north-south direction.
The end of a magnet that points to the north is called the north pole while the end that points to the south is called the south pole. The north pole is indicated by ‘N’ and the south pole, by ‘S’.
- Place some iron filings on a sheet of paper and pass a bar magnet over them. Pick up the bar magnet by holding it in the centre. What do you see ? To which part of the magnet do most of the iron filings stick? On which part do we see fewer filings ? What can we conclude from this ?
The magnetic force is concentrated at the two ends or poles of a magnet.
- Take a bar magnet that can be cut with scissors or a knife. Take iron filings on a sheet of paper and place the magnet on it. Most of the iron filings will be seen to stick to its poles. Now cut the magnet into two pieces as shown in the picture and place those pieces on iron filings. Pick up each of the pieces and observe them. What do you find ?
If a magnet is divided into two parts, two independent magnets are formed. It means that the two poles of a magnet cannot be separated from each other.
- Fix a powerful bar magnet to a stand as shown in the figure. Fix an iron bar at a short distance below the magnet. Take iron filings near the iron bar. What do you see ? After some time take the magnet away. What happens now?
Iron filings stick to the iron bar when the magnet is near it and fall off as soon as the magnet is taken away. That is, the magnetism in the bar vanishes.
A magnetic material acquires magnetism when placed near a magnet. This magnetism is called induced magnetism.
- Fix a bar magnet to a stand as shown in the figure. Let it become steady. Take another bar magnet near the hanging bar magnet. Observe what happens. Do the same again and again, exchanging the ends of the magnet. What do you see ?
There is repulsion between like poles of a magnet, while there is attraction between the opposite poles.
- Take a needle or nail. Place it steady on a table. Keep on rubbing a magnet over it from one end to the other. Do this 7-8 times. Now take a few pins near that needle/nail. What is seen? In this way, magnetic objects acquire magnetism. Magnetism of this kind is temporary. It lasts for a short while.
During the above activity we saw that the pins stick to the nail. Now stop the electric current and see what happens. The pins sticking to the nail fall off. Why does that happen? Magnetism is produced in the nail due to the electric current. When it is put off, the magnetism vanishes. Such a magnet is called an electromagnet. This magnetism is temporary. Electromagnetism is used in many places in our day-to-day life.
For example, it is used in instruments such as a door bell and a crane. On the other hand, the magnets fixed to a pin holder or the door of a cupboard are permanent magnets. Permanent magnets are made from a mixture of nickel, cobalt and iron. For example, the material alnico is a mixture of aluminium, nickel and cobalt.
In the past…
The British scientist Michael Faraday developed the technique of producing electricity with the help of a magnet. Michael Faraday was born in a poor family. As a young boy, he had to work with a book seller. There, he read many books and developed an interest in science. Later, he went on to do research at the Royal Institution in London. It is due to Faraday’s research that today we can use electricity and electromagnetism in innumerable instruments in our day-to-day life.
How is magnetism destroyed?
Magnetism gets destroyed when a magnet is heated, thrown, knocked about or broken into pieces. Therefore, it is important to store magnets carefully. A piece of soft iron is placed in the box in which a magnet is kept. The bar of soft or pure iron protects a magnet, therefore, such a bar is called a magnet keeper.