Properties of a Magnet

Summary

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Substances that possess the property of attracting iron are called magnets. The two ends of a magnet are called its poles. All magnets have two poles, namely, the north pole and the south pole.  In order to identify the poles, the north pole is usually painted in red colour. The other end of the magnet will, therefore, be the south pole. In laboratories, magnets are painted completely red in colour with a white dot to indicate the north pole. 

Types of Magnets
Magnets can be classified into natural and artificial magnets. A material which occurs naturally and possesses magnetic properties is called a natural magnet, e.g. magnetite (lodestone). A material which is made into a magnet by artificial means is called an artificial magnet. Artificial magnets are made by magnetising different shapes of magnetic materials. A rectangular iron bar, an iron needle, a blade or an iron nail can be turned into a magnet by rubbing a bar magnet over it. Hence artificial magnets can be of diffrent shapes, e.g., bar magnets, cylindrical magnets, dumb-bell shaped magnets, horseshoe magnets, etc. Also, artificial magnets are more powerful than natural magnets.

Magnets can also be made using electricity. An electromagnet is made by passing an electric current around an iron piece. Magnets which lose their magnetic property when the cause producing the magnetism is removed are called temporary magnets. Electromagnets and magnets made of soft iron are temporary magnets. Magnets which do not lose their magnetic property even when the cause producing the magnetism is removed are called permanent magnets. Magnets made of steel are permanent magnets. The strongest magnets are made of an alloy containing aluminium, nickel, iron and cobalt (ALNICO). Even small magnets of ALNICO are strong enough to lift hundreds of times their own weight.

Compass 
A compass is an instrument which is used to find the directions. It has a thin magnetic needle supported from a pivot so that it can rotate freely. The needle is placed over a dial with the directions marked. The entire assembly is placed inside an airtight box. The north pole of the magnetic needle is painted red. The magnetic needle in the compass points in the north-south direction. By aligning the dial properly, the directions can be found. In the ancient days, an old pointing device called the south-pointing fish was used to know the directions, in which the head of the fish pointed towards the south.

Properties of Magnets

  • A magnet attracts magnetic materials towards itself.
  • A freely suspended bar magnet always aligns in the north-south direction.
  • Unlike poles attract each other and like poles repel each other.
  • A magnet with a single pole does not exist.  If a magnet is cut into two pieces each piece will behave like an independent magnet, with a north pole and a south pole.
  • When a bar magnet is rubbed over an iron bar, it changes the iron bar into a magnet.


Storing Magnets

If a magnet is left to itself over a long period of time it gets demagnetised, i.e. it loses its magnetic property. To avoid this, when not in use, magnets are stored between soft iron pieces called keepers. To protect magnets from demagnetisation, bar magnets are arranged in pairs with their opposite poles facing each other and two soft iron pieces are placed at the two ends of the pair of magnets. 

Precautions to Protect Magnets from Losing Their Magnetic Properties

  • Never drop magnets from heights.
  • Never heat a magnet.
  • Do not hammer a magnet.

Certain items such as CD's, DVD's, debit cards, credit cards or ATM cards, audio and video cassettes, and mobile phones contain magnetic material. Keep them away from magnets to prevent damage.

Uses of Magnets

  • Magnets are used in making magnetic compasses which help sailors and navigators to know the directions.
  • Magnets are used in magnetic toys, stickers, refrigerator doors, etc.
  • Magnets are used for separating iron from ores containing other non-magnetic substances.
  • Electromagnets are used in generators, motors, loud speakers, telephones, TV sts, fans, mixers, electric bells, etc.
  • Electromagnets are used in cranes to lift heavy iron bars and to separate iron objects from scrap.
  • Eye doctors use magnets to remove tiny iron pieces that have accidentally fallen into the patient's eye.

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Activities & Simulations

Activity 1

Learnthings.co.za has created a a virtual activity to learn that when two magnets are put together there are forces between them. It demonstrates the attatraction and repulstion forces. 

We can drag each object into the sentence and click to predict the magnetic or non-magnetic objects.

Go Activity



Activity 2

Aartpack  has created a virtual activity to understand the laws of magnetic poles. i.e. the similar pole of magnets repel and the opposite forces attract each other.  that when two magnets are put together there are forces between them. It demonstrates the attatraction and repulstion forces. 

We can drag each object into the sentence and click to predict the magnetic or non-magnetic objects.

Got Actitivity

1 . Q: Which is the surest test of magnets?

Repulsion is the surest test because any substance made of iron,nickel, cobalt will also have attraction but won't have repulsion.

2 . what will happen when a magnet brought near a compass

When a magnet is brought near a compass the needle of compass gets deflected due to the magnetic field of the magnet.

Good l...

3 . Why do doors of refrigerator have week magnetic strip

The strip is weak because it should be easy to open the doors and also it should be just strong enough to attract the open refrigerator door...

4 . In which direction will a magnet point if it is freely suspended in space?

It would point in a north-south direction, since, the earth itself behaves as a huge bar magnet, the north pole would get attracted to the g...

5 . what will happen if a compass is brought near a magnet?

If a compass is brought near a magnet its needle gets deflected due to the magnetic field of magnet.
good luck...

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