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Magnet

Published by: BhumiRaj Timalsina

Published Date: 31 Jan 2022

Magnet in Grade-6 , Reference Note

Introduction

A magnet attracts iron pieces towards it. A magnet can be used to pick up and collect small iron pieces from the floor. It is also used to pull out tiny iron pieces from ear or eye when it happened to enter into them accidentally. Magnet is one of the important component in the constructions of radio, transistor, speaker, telephone and other electric equipments. Similarly it is one of the important component in the construction of electric generators and electric motors. Thus a magnet plays an important role in the development of modern electric equipments. There are two magnetic poles at each end of bar magnet. At one end there is magnetic north pole and at the other end a south pole. The energy of a magnet is termed as the magnetic energy.

Magnetic property:

1. Attractive property: 

A permanent magnet has the property of attracting the magnetic materials towards it. The objects which are attracted by a magnet are termed as the magnetic materials. Iron, cobalt, nickel, and some alloys are attracted by a magnet. When a bar magnet in dipped into iron fillings,they stick only near the ends or poles of a bar magnet. It shows that the magnetic effect is concentrated at the poles of a magnet. These poles always occurs in pairs which are of equal strength.

2. Directive property:

The two ends of a freely suspended bar magnet always point roughly towards the geographical north and the south poles. The north seeking (north pole) always points roughly towards the geographical north pole and the other end towards south. This property of a magnet is Magnet attracts iron fillings. 44 Science and Environment, Class - 6 known as the directive property of the magnet. Similarly two ends of a compass needle always points towards the geographical north and south pole. A compass needle is pivoted at its centre so that it can rotate freely. It is then kept inside in small case (a small box). The top surface of the case is covered with a transparent glass piece. Similar to a compass needle, a bar magnet if made to float on water surface with the help of a cork (or some light solid plastic), comes to rest such that its one end points towards the geographical north and the other south.

Activity 1:

Suspend a bar magnet by an unspooned thread, such that the bar is horizontal, when suspended freely. There should be no other magnetic material close to it, in this experiment. The two ends of the bar magnet point north and south poles when it comes to rest. To conform this test swing it by a careful and gentle push on its end. After completing a certain number of swings, it again comes to rest pointing north and south. This property is known as the directive property of a magnet.

3. Magnetic strength is concentrated at the ends of a magnet

Activity 2

A magnet has more magnetic force at it sends. It has the least ar about nill magnetic force at its middle line. It can be understood by following activity. The activity shows that like poles repeat and unlike poles attract each other. Take some iron fillings on a sheet of paper. Put the bar magnet over it and then suspended it by an un-spooned thread. It will be found that the stick only near the ends of the bar magnet and no fillings at the middle of the bar. 

4. Like poles (N-N) or (S-S) repel and unlike poles (N-S) attract each other:

The north pole of one magnet and the north pole of another magnet, similarly (S-S poles) are like poles. When two similar poles of the magnet are brought close to each other, they get repelled with each other. But the unlike poles (S-N) attract each other. It can be shown using a compass and a permanent magnet. It will be found that N-pole of the compass is pushed away when the N-pole of the bar magnet is brought close to it.

Activity 3:

Hang a bar magnet freely to move. Bring the north pole of another magnet close to the north pole of the hanging magnet. It is found that the north pole of the suspended magnet is pushed away. Again bring the south pole of the suspended magnet near the north pole of the suspended magnet. It is found that the poles are attracted towards each other. The activity shows that like poles repel and unlike poles attract each other. The activities shows that like poles repel and unlike poles attract each other.

5. Magnetic poles always exist in pairs:

The poles of a magnet always exist in pairs as north and south. The poles cannot be isolated. We cannot get a magnet having a single north or a south pole. A new pole will be developed at the region where we divide and sub-divide a magnet. Thus in a magnet the poles always exist in pairs which are of equal strength. Like poles repelled

Activity 4:

Take a razor blade. Break it into two parts along the sharp edge. Keep one piece over a table. Now touch the S-pole of the external magnet at one end of the blade and slide it along PQ as in the diagram. Repeat the process for about 20-25 times. Note the resultant polarity on the razor blade with the  help of a compass. Break the razor blade again into two pieces at its middle. It will be found that there is one new magnetic pole developed at each piece. Check the nature of the new magnetic polarity using a compass. If we divide and sub-divide the razor piece again and again, at each time we get a pair of magnetic poles, however small it may be. This activity shows that magnetic poles always exist in pairs.

Magnetic and non-magnetic substance:

A magnetic substance is attracted by a magnet. Iron, cobalt, nickel, and some alloys belong to the magnetic substance. These metals can be magnetized by different methods as single touch method, electric method etc. The non-magnetic substances are not attracted by a magnet. The metals, as gold, silver, brass, etc come in the family of non-magnetic substances. These metals cannot be magnetized by any methods. Magnetic poles The region of a magnet from which the magnetic forces appear to originate is known as the magnetic pole. It lies a little inside the body of the bar magnet from its end. For example if the real length of a bar magnet is 10 cm , then the distance between the poles will be 8.5 cm. The distance between the poles of a magnet is called the magnetic length. The magnetic force of a magnet appears to concentrated at the ends of the magnet.

Activity 5:

A rough and approximate method to get the position of the poles is discussed below. Put a bar magnet on a sheet of white paper and draw its outline. Draw a dotted pencil mark along the length of the outline which runs centrally in the outline. Put a compass at different positions as 'X', Y, 'Z' as shown in the figure near one end of the magnet. Put the pencil marks at the two free ends of the compass needle. Join those points which meet at N and S respectively. These points represent roughly the position of the magnetic poles. Measure the magnetic  length N-S and the real length of the magnet. Theoretically, the ratio between the magnetic length to the real length of the magnet comes about 0.85.

Magnetic field:

A magnet can attract magnetic bodies up to a limited area only around it. Thus there is a fixed place around a magnet to which the magnet can affect on magnetic bodies which is called magnetic field of the magnet. Some magnets have wide magnetic field and some have narrow magnetic field, By using a magnetic compass we can plot the magnetic field of magnet . Now do the following activityto detect the magnetic field of the given magnet.

Activity 6:

To get the general idea of the magnetic field of a magnet, we take a sheet of white paper and a bar magnet. Remove all the magnetic substances from the experiment table. Put the paper on the table. A bar magnet is placed on the paper. Draw its outline. Put a compass near one end of bar magnet. The compass needle will be affected by the magnetic force of the bar magnet. Slowly move the compass away from the magnet till the compass needle shows no effect on it. The procedure is repeated at different positions till we get a closed area surrounding the magnet. This area in which the compass needle detects the magnetic force is the magnetic field of the given magnet.

 

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