Magnetism

Discovery of Magnets

Yes, you are right. That is a magnetic rock. People found it attracting not only for the stick of Magnus, but also for all the materials made of iron. The more rocks of these kinds were found worldwide. These magnetic rocks were named 'Magnets' and the ore is called as 'Magnetite' after the name of the boy Magnus. The name is also supposed to come after the name of the place (Magnesia) in which it was found. Magnetite was the ore with attracting property found in that region. Magnetites are natural magnets. They are called magnetic stones. Natural magnets do not have a defi nite shape. Since, they are used for fi nding direction, they are also called 'leading stones' or 'lode stones'.

Magnet of different shapes

After learning the method of changing the piece of iron into magnet (magnetization) we have been making and using several kinds of magnets. Such man-made magnets are called artifi cial magnets. Bar-magnet, Horseshoe magnet, Ring magnet and Needle magnet are generally used artifi cial magnets.

Magnetic and Non Magnetic Materials

Substances which are attracted by magnet are called magnetic substances. Iron, cobalt, nickel are magnetic substances. Substances which are not attracted by magnet are called non-magnetic substances. Paper, plastic are called nonmagnetic substances.

Finding directions with a magnet

Tie a piece of thread to the centre of a bar magnet and suspend it. Note, in which direction the magnet stops. Draw a line on a sheet of cardboard or the table along the direction in which the bar magnet stops (i.e) a line parallel to the bar magnet). Turn the magnet gently and let it come to stop again. Repeat it three or four times. This is roughly the north-south direction. The end of the magnet that points to the north is called the North Pole. The end that points to the south is called the South Pole. A freely suspended magnet always comes to rest in north-south direction.

Magnetic compass

A compass is an instrument which is used to find directions. It is mostly used in ships and airplanes. As a rule, mountaineers also carry a compass with them so that they do not lose their way in unknown places. The compass has a magnetic needle that can rotate easily. The marked end of the needle is the North Pole of the magnet. Can you use magnetic compass to fi nd west direction? Ask your teacher to help you in using magnetic compass.

Storage of Magnets

Improper storage can also cause magnets to lose their properties. To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side. They must be separated by a piece of wood and two pieces of soft iron should be placed across their ends. For a horse-shoe magnet a single piece of soft iron can be used as a magnetic keeper across the poles.

Usage of Magnets

We use various equipment with magnets in day to day life. Discuss with your friends about the usage of the magnets in the following instances.

Science Today – Bullet Trains

How does the electromagnetic train work?

Electromagnets are used in Electromagnetic train. Electromagnets are magnetised only when current flows through them. When the direction of current is changed the poles of the electromagnets are also changed. Like poles of the magnets which are attached at the bottom of the train and rail track repel each other. So, the train is lifted from the track up to a height of 10 cm. We Know that we can move any magnetic object with the force of attraction or repulsion properties of magnets. This train also moves with the help of the magnets attached on the sides of track and the magnets fitted at the bottom sideway of the train. By controlling the current we can control the magnets and movement of the train. As there are no moving parts, there is no friction. So, the train can easily attain a speed of 300 km per hour. These trains are capable of running up to 600 km/ hour. They do not make any noise. They require less energy and they are eco-friendly. Even though, many countries have taken effort to use these trains, such trains are used for public transport only in China, Japan and South Korea. In India the possibilities of introducing these trains are under consideration.