⛪Home⇐ Class VI Playing With Magnets


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Class VI - Science: Playing with Magnets
One Word Answer Questions:
Q) An object which attracts magnetic materials like iron, cobalt and nickel is called?
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Q) Who discovered magnet?
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Q) Give an example of an artificial magnet?
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Q) What are the materials called that are attracted towards a magnet?
    
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Q) Name the device which is used to find East-West direction at any place?
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Short Answer Questions:
Q) State any two properties of a magnet?
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Q) Where are the poles of a bar magnet located?
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Q) What is an Electromagnet?
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Q) Mention any two methods by which a magnet can be demagnetized.
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Q) How is a compass used to find directions?
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Q) Write a short note on the interaction between the poles of a magnet.
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Long Answer Questions:
Q) What is a magnet? Explain the poles of a magnet?
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Q) Differentiate between magnetic and non-magnetic materials with examples?
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Q) How to make an iron strip act as a magnet?
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Q) How does a compass work and how can it be used to find direction?
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Activity:1
  • Take a pin holder from your school office.
  • Drop some pins, jump-clips, iron nails into it.
  • What do you observe? Do the same with a piece of paper, a pencil and an eraser.
  • You would notice that some of these objects (pins, jump-clips, nails) get stuck to the top of the pin holder while the other objects (paper, pencil, eraser) fall into the pin holder.
  • Why does this happen so?
  • The cap of the pin holder contains a magnet which attracts substances like iron pins, iron nails etc.
  • Similarly, the metal stickers also have a magnet at the back so that they can stick to iron doors
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Activity:2
Can we separate iron filings from soil?
  • Take a bar magnet and roll it in the soil in your school ground for some time.
  • Pull out the magnet. What do you find? Does anything get attached to the magnet?
  • You may find some dark particles of soil sticking to the magnet.
  • Now gently remove these dark particles from the magnet and collect them in a sheet of paper. These are iron filings.

Activity:3
  • Spread some iron filings uniformly on a sheet of paper.
  • Place a bar magnet below this sheet. the pattern of iron filings spread over the sheet?
  • You will observe that the uniformly spread iron filings concentrate at two points of the paper sheet.
  • At some distance you will find some scattered iron filings between these two points.
  • This change in the spread of iron filings on the sheet of paper is due to the magnet present below it.
  • The iron filings move towards its ends because of this magnet.
  • Thus the ends of the bar magnet attract more iron filings than the middle part of the magnet.
  • By this activity we can conclude that every bar magnet always has two ends whose attracting capacity is more than its other parts. These ends are called poles of the magnet .
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Activity:4
Finding directions with a bar magnet.
  • Suspend the bar magnet freely with the help of a thread tied around its center.
  • Does the magnet remain stationary?
  • Wait for some time. What do you find now?
  • Electromagnets are made up of an arrangement of wire coils; often, the wire is wound around a ferromagnetic substance such as steel.
  • You will notice that the magnet finally takes a position in the North-South direction.
  • Mark the end that points towards the North with some colour.
  • Now disturb the magnet and again wait for some time.
  • Magnets always come to rest in the North-South direction.
  • In each case the marked end points towards North. This end is known as North pole of the magnet.
  • The other end, which points towards the South is known as South pole of the magnet.
  • This property of magnets is called directional property.
  • It is exhibited only by magnets.
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Activity:5
  • Place a bar magnet on a table in any direction.
  • Suspend another bar magnet over .
  • The suspended bar magnet should be fairly close to the one kept on the table.
  • Observe in which direction the suspended bar magnet comes to rest.
  • The suspended bar magnet always comes to rest in the direction of the bar magnet placed on the table.
  • But the north pole of the suspended bar magnet points towards the south pole of the bar magnet placed on the table and south pole of the suspended bar magnet points towards the north pole of the bar magnet placed on the table.
  • In this case the suspended magnet comes to rest in the North-South direction.
  • We can say that there is some magnet below the suspended bar magnet which compels it to come to rest in that particular direction (as in above two cases).
  • Where does this invisible magnet come from? The earth possesses magnetic property which acts upon the suspended bar magnet .
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Activity:6
  • Make your own magnet Take an iron nail and place it on a table.
  • Make sure that the nail neither attracts nor repels iron pins or iron filings.
  • Take a bar magnet and place one of its poles near one edge of the nail.
  • Without lifting the bar magnet, move it along the length of the iron nail till you reach the other end.
  • Then lift the bar magnet, bring it to the first end of the nail and move along the length again Repeat this process 20-30 times.
  • Now remove the bar magnet and bring some iron filings or alpins close to the nail.
  • What do you notice? The iron filings or alpins get attracted by the nail.
  • Thus you have succeeded in making your own magnet by magnetizing the nail.
  • What will happen if the nail is now suspended freely?
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Activity:7
  • Make your own magnetic compass Take a magnetized needle.
  • Tape the needle to a light cork. Float the cork in a glass of water .
  • Add a little detergent to water to help the cork float freely.
  • In what direction does your magnetized needle point?
  • It points in NorthSouth direction.Thus it acts as a magnetic compass.
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Activity:8
  • Magnetic induction Take a safety pin and bring it close to an alpin.
  • Does it attract the alpin? Why? Bring the safety pin close to one pole of a bar magnet and see how it gets attached to the magnet.
  • Now bring an alpin and touch it to the safety pin .
  • (a). Does safety pin attract the alpin? Why?
  • In the above two cases, we notice that the safety pin acts as a magnet when it is in contact with another magnet.
  • Magnetic property is induced in safety pin due to the bar magnet.
  • Magnetic property possessed by a magnetic substance due to the presence of a magnet near it, is called magnetic induction.
  • Take a bar magnet in one hand and a safety pin in the other hand, hold them in such a way that they are close to each other but not in contact .
  • Bring an alpin and touch the safety pin.You will notice that the alpin will stick to the safety pin. This shows that due to magnetic induction safety pin acts as a magnet.
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Forms of Water

All of us know that water is available in nature in three forms.

Solid Form
We call solid form of water ice.
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Liquid Form

If we heat ice, it will change into water. Water in liquid form is present in oceans, seas, lakes, rivers and even underground.

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Gaseous Form
  • The gaseous form of water is water vapour which is present in the air around us.
  • We know that when ice is heated it converts into water and if water is heated it turns into water vapour.
  • Similarly when water vapour is cooled.
  • If water is cooled further we will get ice. So, we understand that these three forms of water are interchangeable.
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Method             Method
                ICE     ↔     WATER     ↔     WATER VAPOUR
Cooled               Cooled

Activity:1
  • Take some water in a glass. Add some pieces of ice to it.
  • Observe for few minutes.
  • What changes do you observe on the outer surface of the glass? You would observe formation of small drops of water on the outer surface of the glass.
  • Why are these drops formed? Do they get formed if there is no ice in the glass?
  • Air around the glass contains water vapour which is warmer than the surface of the glass.
  • Due to the cold glass, air close to its surface will also become cooler.
  • This changes the water vapour in the air around the surface of the glass into water and forms small drops on the outer surface of glass.
  • Have you ever observed in your daily life where water vapour changes into water? List them out.
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Activity:2
  • Clouds in kitchen Take a vessel filled with water.
  • Keep it on a stove and heat it slowly. Observe for some time.
  • Now cover the vessel with a plate.
  • Remove the plate after a couple of minutes Do you see any changes on the inner surface of the plate?
  • Pour some cool water on the plate and observe what happens?
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  • What similarities do you find between evaporation of water from surface of water bodies and evaporation of water from a bowl heated in the kitchen?
  • From both cases discussed above, we know that water vapour helps to form clouds.
  • The clouds formed on the surface of the different water bodies do not stay there.
  • They start to move from one place to another in the direction of winds.
  • As more clouds come together they become laden with water vapour.
  • Winds bring the clouds from the sea to the land.
  • The colder air in the upper layers of the atmosphere cools the clouds.
  • Have you observed the colour of a cloud before rain?
  • How are clouds converted into rain? We all know that without clouds, it will not be possible to get rains and that all clouds do not cause rains.
  • Some changes take place in the clouds before they cause rain.
  • What changes do you notice in the sky and in the atmosphere before it rains?
  • What changes take place in clouds before raining?
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  • The clouds moving in air are generally at higher levels.
  • Sometimes the cool breeze coming along with air makes the clouds cooler.
  • This leads to water droplets present in the clouds to condense and form large water drops.
  • Further cooling of clouds increases the size of their water drops and clouds become heavy and descend towards the earth.
  • The colour of such clouds changes from white to gray giving us the feeling of dark clouds gathering.
  • When the size of the water drops increases further it becomes difficult for the cloud to hold them and water drops begin to fall. This is called "rain".
  • In our daily life, we observe that before raining, clouds descend towards the earth’s surface and we experience a cool breeze before rainfall.
  • In very cold conditions, the drops of water turn into crystals of ice and fall as snow.
  • Sometimes big drops of water solidify into ice and fall as pieces of ice known as hailstones.
Introduction

“A body, as a piece of iron or steel, that possesses the property of attracting certain substances such as iron, is known as a magnet".
You may not see them, but magnets are everywhere. Our car motors, phones, tape recorders, credit cards, stereo speakers and computers, to name just a few practical applications.

examples of magnet
Examples of magnets in everyday life
Discovery Of Magnets

  • A Greek shepherd named Magnets discovered magnets more than 2500 years ago in Magnesia, Greece.
  • Magnets discovered a natural magnetic rock, called the lodestone.
  • In the form of a bar, it was used to find directions on the earth, and so the name lodestone, which means the stone that leads.
  • Lodestone has a compound of iron called magnetite. The name magnetite has been derived from Magnesia or Magnets.
  • Magnets are named after magnetite. Natural rocks that have the property of attracting iron are called natural magnets.
  • The force that magnet exerts in iron is known as magnetic force.
  • Archimedes, the ancient Greek scientist, is believed to have used lodestone to pull nails from enemy ships, which made the ships, sink.
lodestone
Lodestone

Now a days, artificial magnets are prepared in different shapes.
For example, bar magnet, horse shoe magnet, cylindrical or a ball ended magnet.

shapes of magnets
Different shapes of magnet

Magnetic And Non-Magnetic Materials
Magnetic Materials:

Materials that are attracted by a magnet are called magnetic materials.
Examples of magnetic materials include iron, cobalt, nickel, steel, etc.

Non-Magnetic Materials:

Materials that are not attracted by magnets are called non-magnetic materials.
Examples of non-magnetic materials include rubber, plastic, stainless steel, feather, paper, mica, gold, silver, leather, etc. Modern coins are made of uniform mixtures of different metals in such a way that they become non-magnetic.

lodestone
Magnet and Non-magnetic Materials
Poles Of Magnet

  • 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.

Let us see which regions in a magnet have stronger magnetism.

‣Put some iron filings on a sheet of paper.
‣ Roll a bar magnet in the filings and then lift it up.
‣ You will find that most of the iron filings stick to the magnets at the ends.
‣ There are fewer iron filings in between and almost none at the centre.
‣ Thus, in a magnet, the regions of strong magnetism are near the ends, which are poles of the magnet.


iron sticking Poles of magnet
Iron Filings Sticking To The Poles Of A Magnet
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 different 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.
compass
The Magnetic Compass
Making Magnets

    A piece of iron can be magnetized by using a magnet in the following way.

  • Place an iron needle or a bar on a table.
  • Hold it down firmly and stroke it about 30 times, from one end to the other with one pole of a bar magnet.
  • After you reach the other end, lift the magnet high and bring it back to the first end.
Making of own magnet
Making Your Own Magnet
  • You will find that if you stroke with the north pole of the magnet, the end of the iron bar from which the stroking is started becomes the North Pole.
  • The other end becomes the South Pole.
  • If you stroke with the South Pole, the poles in the iron needle will be reversed.
  • This is known as single touch method of making magnets.
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.
Storing of magnet
Storing A Magnet

Precautions to Protect Magnets from Losing Their Magnetic Properties

  • Never drop magnets from heights.
  • Never heat a magnet.
  • Do not hammer a magnet.
Magnets Lose Their Property On Heating, Hammering And Dropping
Storing 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, 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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