CLASS

VI

UNIT-7

CBSE - i

Science PHYSICS

MAGNETISM

CENTRAL BOARD OF SECONDARY EDUCATION Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India

CBSE - i

Science PHYSICS

MAGNETISM CLASS

VI

UNIT-7

CENTRAL BOARD OF SECONDARY EDUCATION Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India

The CBSE-International is grateful for permission to reproduce and/or translate copyright material used in this publication. The acknowledgements have been included wherever appropriate and sources from where the material may be taken are duly mentioned. In case any thing has been missed out, the Board will be pleased to rectify the error at the earliest possible opportunity. All Rights of these documents are reserved. No part of this publication may be reproduced, printed or transmitted in any form without the prior permission of the CBSE-i. This material is meant for the use of schools who are a part of the CBSE-International only.

Content v Preface v Acknowledgement v Syllabus Coverage

1

v Scope Document

2

v Matrix

3

v Teacher Notes (TN)

5

v Teacher – Student Support Material (TSSM)

20

1. Introduction

21

2. Type of Magnets

23

3. Magnetic and Non-magnetic Materials

24

• Activity 1

24

• Worksheet 1

27

• Worksheet 2

28

• Activity 2

31

4. Magnetic Poles

32

• Activity 3

32

• Activity 4

34

• Activity 5

35

5. Magnetic Compass

37

6. Properties of Magnet

37

• Activity 6

38

• Worksheet 3

40

7. Magnetic Field

41

• Activity 7

42

• Activity 8

43

8. Attraction and Repulsion Between two Circular Magnets

44

9. How to Make your own Magnet !

45

• Activity 9

46

• Activity 10

47

10. Demagnetising

48

11. How To Keep Magnet Safe

48

• Formative Assessment

49

• Activity 11

50

• Activity 12

51

• Activity 13

52

12. Use of Magnets

53

• Summary

56

• Summative Assessment

57

• Recapitulation

61

• Vocabulary Building

63

• Acknowledgment

64

• Resource

65

• Rubric: Assessment For Learning

66

Syllabus Coverage MAGNETISM S Y L

 Magnets and their properties.  Magnetic poles and magnetic compass.

L A B U

 Magnetic field.  Testing strengths of magnets.

S

1

Scope Document Intended learning outcomes: At the end of the chapter the students would be able to: 

Classify some materials as magnetic and others as non-magnetic.



Distinguish between natural magnets and man-made magnets.



Observe that each magnet contains two opposite poles.



Use a magnetic compass.



Explain the concept of magnetic force of attraction and repulsion.



Get a basic idea of the ‘molecular picture’ of a magnet.



Understand the term ‘magnetic field’.



Demonstrate and illustrate the pattern of magnetic field using iron filings.



Use simple methods of testing the strength of a magnet.



Explore different uses of magnets.



Learn to make temporary magnets

Cross Curricular Links Chemistry - Apply concepts of different type of materials. Mathematics - Apply concepts of comparing the strength of different magnets by measuring the force of attraction and repulsion. English/Languages– listening, Speaking, reading and writing in investigating, planning, research and presenting information. Information Technology- Making Power Point presentation using animation skill and surfing for interesting and relevant extended learning.

2

History - The discovery of magnetic property can be traced back to the story of a shepherd boy in the town of Magnesia.

Matrix CONTENT Introduction: Magnet, video Clip (1) Magnets attract objects made of iron. Method; Use various

SKILL Observation, Making connections. Hands-on-experience. Logical and analytical.

examples from day to day

INTENDED LEARNING Understand the concept of magnetism. Relate attraction with other materials. Magnets attract some objects.

life.

Magnets are of different shapes.

Type of Magnets: Demonstration

Separate metals based

Identify and differentiate

on careful observation

magnetic and non

of the magnetic

magnetic materials.

behavior, Hands on experience, Properties of a magnet,

Appropriate handling of

Each magnet has two

Magnetic Poles, Magnetic

apparatus; team work,

poles.

Compass

logical and analytical skills, Observational,

Opposite poles of magnets attract each other and like poles repel each other

3

Magnetic compass can be used especially to locate direction in unfamiliar land and adventure games,. Magnetic field, Magnetic

Resourcefulness in

To have fun with pattern

field lines,

creative conjectures,

by drawing a magnetic

Drawing skill Magnetize magnetic objects,

Vocabulary

demagnetisation

development,

Artificial and permanent

Team work, Learning by

magnets

doing

field. To make their own magnet . Differentiate between artificial and permanent magnets

Making of a Magnet Laboratory Strength of magnet, Use of

Use magnets at a small

Differentiate between

magnets

and large scale. Group

strong and weak magnet

work, Learning by doing, Comparison, Electomagnetism Example of door bell

Observation, scientific and IT skills

Understand how magnets can be used Gain knowledge on how electric current induces magnetism

4

Teacher Note (TN) You would have definitely wondered sometime why an object always falls downward after being thrown up. You can show this by throwing a chalk piece or a duster upwards. The most general reply would be the attraction due to the earth. Now you can ask the students about other substances that attract any other substance. Try to help them visualize.

Activity 1 To build the background knowledge, introduce the unit by showing a magnet song in video clip–1. Ask the same question and try to elicit answers from the students. Discuss the variety of answers with them. Discussion from the day-to-day experiences will enable you to build the discussion in a progressive way in the class. History One of the ancient ways of getting knowledge is Story telling. Children are always fascinated by stories. This helps them to visualize. You could relate to the students the story of a shepherd boy of town of Magnesia who first noticed his crook was pulled down whenever he passed a certain rock while he had taken his sheep out for grazing. You could tell them what a crook is and ask the students what could be the reason for crook getting pulled down. This question would give an opportunity to the students to brainstorm and apply their knowledge they acquired when the teacher showed them the video clips. You would be able to elicit from the students that the rock must be a magnet that attracted the iron end of the crook.

5

At this point facilitate the students to understand why this rock behaved like a magnet. Introduce the term lodestone (also written as loadstone), which is a piece of iron that acts as a magnet. The rock that pulled crook down was known as lodestone (loadstone). You may ask the students to explain if it is possible to use a strong magnet to remove the screws or nails from the joints of a wooden box or if the nails used to hang a wall painting could be pulled out by a strong magnet. Such questions will enable the students to enhance their thinking skills and will help the teacher in making the topic more interesting. Relate the famous incident when Greek Scientist Archimedes is believed to have used lodestone to pull nails from enemy ships, which then sank. Tell the students about the rag/scrap pickers who are seen with a stick, the end of which is attached with a magnet. They are often seen picking up the iron wastes from the scrap. Unknowingly, they are using the property of Magnetism. They are not aware but they are the scientists in the making. Emphasize that we all have little scientists in us and the use of science is in our day-to-day life. The budding scientists thus come up and bring innovations. The terms used will help to enhance vocabulary of the students. With these stories you could keep the interest of the students alive to know more and to explore more about Magnet and Magnetism. Make a web-chart of teaching points keeping in mind the learning outcomes of the students. Following teaching points could be covered in this unit: 

Shapes of magnets



Natural & Artificial magnets



Common types of magnets 6



Properties of magnets



Magnetic and non-magnetic materials



Magnetic poles: North seeking pole and South seeking pole



Magnetic forces & Magnetic field



Applications of magnetism



Magnetization of materials



Electromagnetism



Uses of magnets & magnetism property

Show them few magnets to make them understand that magnets are of different shapes. Give the information that magnets are usually made of iron or steel but some powerful magnets can be made of special alloys of Aluminium, Cobalt, Copper, Nickel. Though the students would be studying this in details in higher classes yet as an extended learning they could explain what an alloy means.

Activity 2 Ask the students to rub an iron clip with a magnet. Observe if this clip can attract an iron pin towards it. Enhance the observational skills of the students through hands-on experience. Observations that the iron clip attracts iron pin. Conclude the iron clip has become a magnet. Tell the students since iron clip has become a magnet it is an artificial magnet. Introduce the term artificial magnets and natural magnets. The term magnetite could also be 7

introduced for naturally occurring magnet as an extended learning. Now, students could be asked to differentiate between Natural and Artificial magnets.

Activity 3 (TSSM Act 1) As a teacher you should be resourceful. Collect various small materials that are easily available at home. Show them how iron nails and pins get attracted by the magnet. Distribute various small objects made up of steel, wood, iron, plastic, Ask students to observe how does each one of them behave when brought close to a magnet. Instruct the students to divide these objects into two groups on the basis of the ones that get attracted by the magnet and the ones that do not get attracted by the magnet. You can introduce two terms, magnetic and non magnetic for the two types of objects. This activity will help the students enhance observational skills, experimental skills and analytical skills.

The answer could be elicited from the students that the magnetic substances are those substances that get attracted to the magnet and non-magnetic substances are those that do not get attracted to the magnet. The students could be asked to define what a magnet is to which they would be able to say that the object that attracts iron is called magnet.

Activity 4 (Worksheet 1) Ask the students to complete worksheet, which will help them, re-enforce the concept studied.

Activity 5 (Worksheet 2) As an extended learning you could ask the students to research and gather information about the presence of magnets in commonly available electrical appliances such as T.V, Refrigerator, Mobile phones, Air-conditioners, Computers etc. The students could then 8

be asked to complete worksheet 2 individually to ensure that the comprehension of concept has taken place. The students will also appreciate the fact that some electrical appliances make use of magnetism. You could show them the parts of a doorbell. The students will be able to relate the significance of magnetism and electricity in their daily life and the curiosity of knowing it can be sparked. Enhance extended learning further by mentioning here the concept of electro-magnetism about which they will study in their higher classes

Activity 5 (TSSM Act 2) Ask the students to take a bar magnet and put a dot of red and black paint at two poles and allow it to hang freely. Ask the students to observe and also draw the hanging magnet. The students will observe that the bar magnet aligns itself in the same direction every time they suspend it freely. Facilitate the students to conclude that a bar magnet has a north seeking pole and a south seeking pole. This is referred to as North (N) pole and South (S) pole of the magnet for the sake of convenience. Molecular Theory of Magnetism All materials contain small particles called molecules. The molecules of iron and steel are magnetic. In a magnet all the molecules are lined up with their own North-seeking and South-seeking poles as in the diagram. This means all south seeking poles are pointing in one direction and all north seeking poles

are

pointing

in

the

other

direction.

9

In an unmagnetised piece of iron or steel the molecules are arranged at random with the poles pointing in different directions. You can show this with a large test tube of iron filings. The tube must be almost full and corked securely. The iron filings can be seen to lie in almost

Iron filings lined up after stroking with

every direction. If you bring this tube

magnet

towards a compass needle, it has almost no effect on the needle. Stroking the test tube, in a horizontal position with the North-seeking pole of a magnet causes the iron filings to line up as in the diagram.

This information is for your reference only. Since learners are getting introduced to magnetism in a systematic way for the first time, avoid burdening their minds with abstract concepts. As an extended learning mentions that the earth is also a magnet and a freely suspended magnet points towards earth’s geographic North and geographic South. Use inter-disciplinary approach to link earth’s magnetic property with that of earths geographic North and South. Ask the students to confirm it by using a magnetic compass needle. Ask four students to stand at the four corners of the classroom, holding magnetic compass. What do they observe? The students will observe that the compass needle rests at geographic NorthSouth direction. Explain the working of a compass needle. You could discuss the role of 10

magnetic compass in navigation. Now a day, we use GPS (Global Positioning System) to find the routes. They will be surprised to know how sailors found their route in sea by using just a magnetic compass. This will enhance the logical and analytical skill among the students.

Activity 6 (TSSM 4) A magnet can attract iron nails or other magnetic materials. But what happens when a magnet is brought closer to other magnet? Does it always attract? Divide the students in the groups of two each and give two bar magnets to each group and ask them to study the behaviour of the two magnets vis-à-vis each other. Ask the group leaders to derive the conclusion from their analysis, which could be as under: 

There is repulsion between the two magnets when their south poles are brought together.



There is repulsion between the two magnets when their North poles are brought together.



The magnets attract each other when the North and South poles are brought together.

Summarize it as: There is repulsion between the like poles of the magnets and there is attraction between unlike poles of the magnets. Show to the students a bar magnet and ask them as to what will happen to its magnetic property if it is cut into two pieces and each piece is again cut into two pieces and so on. This question will make the students think thus enhancing their thinking skills. Organize a brain storming session and let the students describe various ways they can

11

experiment and prove their point. During this brain storming the elicit the answer that each piece of magnet behaves like a magnet. Give a chance to the students to prove the same by asking them to perform an activity (TSSM Act 5). Use discussions as pedagogical strategy to develop communication skills in a group situation. The spoken skills of students may be encouraged along with ability to organize information in a systematic way. Ask them to summarize the proof of the experiment done in the class. Elicit from the students that when a magnet is cut into two pieces each new magnet shows the same properties as that of the magnet from which it is cut. Interestingly you could discuss the concept of regeneration in Planaria. When its body is cut into parts, each part grows to become a complete Planaria. Magnetic field Place a magnet on the top of a table. Now keep another magnet at the corner of the table. Does it show any attraction or repulsion? Move it further close the first magnet. Does it show any displacement?

Continue to move the magnet towards the first

magnet till the first magnet gets slightly displaced. Ask the students to explain the behaviour of two magnets. To make the students understand the concept of magnetic field the teacher could ask the students to sprinkle some iron filings on a bar magnet and note down their observations thus enhancing their observational skills. Elicit from the students that more iron filings get attracted at the poles of the magnet and there are very few at the centre of the magnet. Ask the students to perform an activity (TSSM Act.6) and observe if any pattern gets formed by iron filings. At this stage use the term magnetic field for the pattern represented by the iron filings. Ask the students to define the term ‘magnetic field’ of a magnet thus enhancing their vocabulary. The students would also get an opportunity to apply their knowledge and observational skill to define this term. 12

Magnetic Field Lines Ask them to draw the diagram of the magnetic field as represented by pattern made by iron filings thus enhancing the drawing skills of the students and making the understanding of the concept stronger and everlasting. The pattern formed by iron filings to show magnetic field of a magnet is due to the force by which the poles of the magnet attract iron filings. Introduce the term magnetic force and explain that the force by which the iron filings get attracted by the magnet is called ‘magnetic force’. You could then draw the attention of the students to an iron clip which behaves as a magnet and attracts another smaller iron pin. You could show to the students that iron clip after sometime has lost its capacity to attract an iron pin. Ask students to apply their knowledge and explain why this clip behaved in different manner. Elicit an answer from the students that it behaved as a magnet for sometime only. You could enhance their extended learning and explain to them that an iron piece can be magnetised temporarily and such a magnet is known as a temporary magnet. Facilitate the students to differentiate between permanent and temporary magnets. Can we make our own magnet? Use all opportunity to trigger the learners to take up the exercise to magnetise an iron needle and thus use the term ‘magnetisation’ as vocabulary development and also give them the opportunity to gain hands-on-experiences by involving them in doing an activity (TSSM Act. 7). By doing this activity the students will also experience that the needle will become a stronger magnet of it is stroked by the magnet a number of times and also stronger the magnet more objects will it attract.

13

Ask the students if this magnetised needle can be demagnetised. The teacher could ask them to explore various ways they can try to de-magnetise the needle. Facilitate in building among them the curiosity and scientific skills by allowing them to experiment independently the ways of de-magnetising temporary magnet. After eliciting various answers from the students ask a student to volunteer to summarize the methods of de-magnetisation explored by them. The teacher could add to this list, some more methods that have not been explored by the students. Emphasize on the usage of terms demagnetise and magnetise thus enhancing their vocabulary. Electromagnets Demonstrate to the students the working of an electronic bell (door bell) by facilitating them to recapitulate concept of electric circuit in the unit electricity they have studied earlier. Explain to them how electric current induces magnetism, hence the term electromagnet could be introduced. They could be guided to check websites to find the appropriate appliances for which magnetism is used thus enhancing their IT skills also. Refer suggested resources given in the unit. Activity 8 (Formative Assessment 1) Magnetic strength Guide the students in performing group activities (TSSM Act. 9 - 11). Let them find out how strong the given magnet is. Each group could share with each other their observations and conclude that longer is the trail of pins picked up by a magnet stronger is the magnet. Ask them to perform group activities to find which one out of the two given magnets is stronger than the other. They could be given two bar magnets and few pins to prove which a stronger magnet is.

14

This will be an opportunity for the students to think and plan a the method by using the given materials to prove which magnet is stronger. You could help them conclude that the magnet that attracts the pins from a farther distance is a stronger magnet. The students could be asked to apply their knowledge of magnetic force to explain the concept of strong and weak magnet. Motivate students to make a science model by using magnet individually or in groups thus enhancing their scientific skills, as they would get hands-on experience. They could apply their knowledge about properties of magnets and make some interesting models such as making a pin dance in the air, make a swimming duck move away from the foods she doesn’t want to have. The teacher could then involve the students in brain storming session to note down the uses of magnets. Structured Questions Question 1

We need to protect our electronic gadgets like music player, computer disks or credit cards from magnetic fields. Suggest a way for this so that we keep magnetic fields away from these gadgets. Question 2 Ranjit has a piece of a metal that he thinks is a magnet. He holds it near another magnet towards which it gets attracted. Ranjit says this proves that his metal piece is a magnet. Explain why Ranjit could be wrong.

15

Activity Use a compass (you can also make one for you on your own) and make a map of your school, your home and also the way to your home from school. You can use steps taken by you as unit of distance (or any other unit convenient to you). Note: Do you know that an average person walking normally covers a distance of 30 metres in 37 steps and this fact was used in ancient cartography (map making) usually by spys. (Source: Archaeological Survey of India) Recapitulation: Assess the situation and as time and students’ readiness permits, you may use these questions to anchor their learning in a deeper way. 1. A Suggested List of Questions is provided to you. Frame worksheets according to the specific need of your class. I. Define the following terms. a) Magnet b) Poles of a magnet c) Magnetic force d) Magnetic compass e) Demagnetisation f) Magnetic field g) Strength of a magnet h) Electromagnet

16

II. Distinguish between the following. i) Artificial and Natural magnets j) Magnetic and Non magnetic substances k) Bar magnet and Electromagnet l) Strong and Weak magnet 2. Ask the students to make their own magnet (magnetise iron needle) and find out its North and South Pole. 3. Divide the class into five groups and ask them to get a doorbell. Ask them to write all materials inside it. Also explain the role of electromagnet in a doorbell. Presented below are:

Suggestive Activities: 1. (10 minutes) 

Distribute magnets and have students work together in pairs to discover some of the properties of two magnets.



Students should record their observations and conclusions in the worksheet.

2. Show students how a magnet attracts iron filings. Show its magnetic field and magnetic lines. 

Have students use iron filings and their magnets to demonstrate and learn about the magnetic field lines. Students should try two different orientations of the magnet with respect to the iron filing demonstration.



Ask them to draw the general nature of the field line pattern in their worksheets for each case. 17

3. (10 minutes) 

Distribute bags of different materials and have the students sort the objects into magnetic and nonmagnetic items based on their observation.



Have them place checkmarks on their worksheets beside the objects they believe are magnetic.

4

(10 minutes) 

Get students to propose how they would test the objects for magnetic behaviour.



Return the magnets and let the students test the objects and record the results in their worksheets.



Analyse Go over the results of the magnetism test.



Were there any materials that fooled the students? What do all the magnetic objects have in common? (They are made of metals that usually contain iron.)

5. (10 minutes) 

Ask students why iron-containing objects get attracted to magnets? Does it matter which pole of the magnet is nearer to this object? What happens inside the material when it is exposed to a magnetic field?



Talk about the molecular ‘poles’ aligning with the magnetic field of the magnet.

6. (15 minutes) 

Can you turn an iron-containing object into a magnet?



Have students take a small nail from the material bag and show them how to stroke the nail with the permanent magnet (use two magnets together if your magnets are fairly weak). How can they prove that the nail is now magnetised? (Let them propose methods such as having the nail pick up paper clips.)

18



Can this be demagnetised? (Yes, by heating or by dropping several times or by hammering.)

7. (5 minutes) 

How can we determine which end of the magnet is the N or S pole?



If using a compass or known magnet is suggested, ask students to consider the case when neither of these items was available.



Lead them to the solution of suspending their nail with a string and seeing how it hangs (they now have a compass).



Suspend one group’s magnetised nail with the suspension setup as a demonstration to illustrate how the N and S ends of the nail can be determined.

19

TEACHER STUDENT SUPPORT MATERIAL (TSSM)

20

1.

Introduction: It is said that a shepherd called Magnus first noticed loadstone(Loadestone) while he was passing through the town of Magnesia. He was carrying an iron- crook which got pulled due to the attraction from a certain rock.

Later, it is told that the ancient Greek scientist, named Archimedes used lodestone to pull nails from enemy ships and was successful in creating holes in the ships. This resulted in sinking of their ships.

Similarly, history of science informs that Sailors also used lodestones to help them navigate. They found that when a piece of magnetite was suspended from a thread it came to rest in a North-South direction. Probably this would have been the first use of a crude magnetic compass.

21

Objects made of magnets possess a property to attract things made of iron, or anything that contains iron. They are however able to attract some other metals like cobalt and nickel. Magnets are usually made of iron or steel. Powerful magnets can be made of special alloys of aluminium, cobalt, copper, nickel.

Can we create magnets? Can we make magnets from cobalt and nickel? If yes! Where have you seen it? What is distinct property in iron?

What do iron, cobalt and nickel have in common? What is a magnet made of? Is it only iron or steel?

Some Common Shapes of Magnet 22

2.

Type of Magnets: A. Natural and Artificial Magnets a)

Natural Magnets: A magnet which occurs naturally in the upper layer (crust) of the earth is not made by human beings or machines. It is because of this reason that we call Loadstone as a natural magnet which is different from artificial magnet. Scientists preferred to call loadstone as Magnetite.

b)

Artificial Magnets Any material (usually a metal) to which properties of a natural magnet can be imparted by human effort or artificial means, is called an artificial magnet. This artificial means could include machines also e.g. Magnets made from iron, steel, cobalt and nickel.

Alloy is mixture of metals

B. Some common type of Magnets i) Horseshoe Magnet: The horseshoe magnet has north and south poles just like a bar magnet . This magnet is curved such that both the poles lie in the same plane. Carefully see figure below. ii) Bar Magnet: A bar magnet is a rectangular a magnet that is in the shape of a bar. It has a north and a south pole.

23

iii) Ball-ended Magnet: A magnet consisting of a steel wire with a steel ball attached to each end.

iv)

Round shaped magnet: A magnet commonly used in toys, electric motor and speakers.

3.

Magnetic and Non Magnetic materials (Refer Unit on Classification of Materials) 

Magnetic materials: Substances which are strongly attracted by a magnet or can be converted into a magnet artificially. Example - Iron, cobalt, nickel etc.



Non magnetic materials – Substances which are neither attracted by a magnet nor can be converted into artificial magnets. Example - Stone, Glass, Paper, wood etc.

Activity- 1 Test for magnetic or non –magnetic materials. Learning outcome: there are two kinds of material in nature: Magnetic (that are easily attracted by a magnet) and Non Magnetic (that are not attracted by a magnet). Material Required : 

Bar or horse-shoe magnet



wooden toothpick 24



coin



plastic cup



paper clips



thread



pins



rubber bands



elastic hair bands



tin can



glass



aluminium foil



crayon



nail



paper



school scissors



staples

Procedure: 1. Make five groups of 8 students and ask them to get the above materials. 2. Now ask the students to hold the bar (or the horse shoe) magnet close to each object provided to them. 3. Study all the objects and then classify or group them based on what they know about the materials. 4. Note down the observation (as to whether the objects get attracted to the magnets or not) in an observation table.

25

Observation table: Magnetic / Non-magnetic

Materials Provided 

wooden toothpick



coin



plastic cup



paper clips



thread



pins



rubber bands



elastic hair bands



tin can



glass



aluminum foil



crayon



nail



paper



school scissors



staples

26

Worksheet -1 Here is a list of some common items. Use a magnet to test each item and note.

Material

Gets attracted by the

Does not get attracted by

magnet.

the magnet.

Paper

Pencil

Plastic coated iron clip

Iron Nail

Cork

27

Screw

Crayon

Wire

Worksheet : 2 A.

Find magnets in your house

Directions: Magnets are used in many different ways. For example, automobile industry uses magnets in the vehicles. Did you by any chance come across a broken speaker of a car.! If you take an iron object close to it you could surprise to note the pull of attraction exerted by the speaker component. There is a suggestive list of items usually found in our home. You may research on the internet to study and find out if they have magnets in them. Note your observation in the space below. 28

Item

Does It Have Magnets?

DVD

Fan

Speakers

Television

Can Opener

Refrigerator

29

Computer

Radio

Telephone

A.C

Washing Machine

30

Activity-2 Study the Behaviour of a Suspended Magnet. Learning outcome: The student will be able to understand that, when a magnet is suspended freely with a thread it aligns along earth’s the north south direction. Material: Thread / string Bar magnet Procedure 1. Take a bar magnet. Put a dot of red and black paint at its two ends to mark the north and south pole tentatively. Let the paint dry. Now suspend it freely with a string, as shown in Figure below. Let the magnet come to rest . Take a compass and put it besides the suspended bar magnet carefully, without disturbing the magnet. Try to observe its position in relation to geographical direction of the earth. You will see that the suspended bar magnet always aligns itself in north south direction. Repeat this experiment three to four times; it is found that the same end of the magnet will always swing toward the north pole of the earth. Therefore, it is called the north-seeking pole or simply the North Pole of the magnet.

Fig: compass needle 31

A magnetic compass shows a similar behaviour when it is put on the table away from other material or magnets. So we can see that one end of bar magnet always points towards earth’s north while the other end points towards earth’s south. For the sake of convenience we call these two ends as the North and South poles of the magnet respectively. Thus we can conclude that North Pole of a magnet always point towards north direction and South Pole of a magnet towards south direction, if it is not under any external magnetic field and is suspended freely. 4.

Magnetic poles These are the two ends of a magnet, where there is maximum magnetic force/maximum strength of the magnet. North pole - That end of a bar magnet which always points towards geographic north when the magnet is suspended freely. South pole - That end of a bar magnet which always points towards geographic south when the magnet is suspended freely

Activity- 3 Attractive/Repulsive Forces Between the Poles of a Magnet. Learning outcome: The student will be able to understand that like poles of two magnets always repel each other and their unlike poles always attract each other. Material required: Two bar magnets. Procedure: Take two bar magnets. First identify the poles of both the magnets by suspending it freely. Take a scale and mark the center of the bar magnet. Color the half, 32

which has North Pole of the magnet red, and the other half, which has the South Pole, black. First bring the two red parts of the magnets close to each other. Students will observe, when two like (similar) poles are brought near each other, they move away from each other i.e. they repel each other. Now ask the students to bring the red part and the black part close to each other. When unlike (dissimilar) poles are brought near each other, they move towards each other i.e. they attract each other.

Observation table: Magnet 1

Magnet 2

North Pole

North Pole

North Pole

South Pole

South Pole

North Pole

South Pole

South Pole

Attraction/ Repulsion

From this activity, we conclude that there is repulsion between like poles of magnets, while there is attraction between unlike poles of magnets. In other words like poles always repel each other and unlike poles attract each other.

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Activity- 4 Poles are the Strongest Part of a Magnet Learning outcome: The students will be able to understand that the strength of a magnet is maximum near its two ends i.e, at its poles. Materials required: • Bar magnet • Iron Filings. Procedure 1) Take some iron filings in a glass plate. 2) Bring a magnet close to the iron filings 3) The iron filings get attracted to the bar magnet. 4) The students will observe that more iron filings gets attracted to the two ends of the magnet than the center. 5) The two ends, as we know, are known as the two poles of a magnet.

So we conclude that poles are the parts of a magnet where its magnetic force is maximum. In other words, poles are the strongest parts of a magnet.

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Activity -5 Magnetic Force is Strongest at the ends. Materials Required: A bar magnet, 15 to 20 clips Procedure: 1. Pick up one clip with the pole of the magnet. 2. Place the second paper clip near the first one. You will notice that the second clip clings onto the first one. 3. Keep adding more clips one by one to make a chain of clips. 4. Count the number of clips this magnet can hold. 5. Follow the same, this time the first clip to be placed near the centre of the magnet. This clip clings onto the magnet. 6. Continue with the chain as done before count the number of clips that make a chain at the centre. Compare the two. Is the chain longer in the centre of the magnet or at the poles of the magnet?

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More number of clips get attracted towards poles of magnet

Magnetic attraction maximum at the poles

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5.

Magnetic compass Magnetic compass is a device that has been used for centuries in helping people to find their way. The act of finding out the directions, at unknown places, or at the sea, was carried out with the help of a compass.

A Compass A compass is basically a small magnet that has a needle attached on top of it. When the small magnet in the compass is free to rotate, it’s magnet points towards the geographic north-south direction.

6. Properties of a magnet: 1. One end (north pole) of a magnet always points towards north direction and the other end (or south pole) of a magnet always points towards the south direction. 2. Like poles always repel each other and unlike poles attract each other. 3. Magnetic force is stronger at the poles of a magnet than at the centre of a magnet.

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What happens when a magnet is cut into pieces? If a magnet is cut into two (or more) parts then each part behaves as a complete magnet. If we keep on dividing the magnet, we will keep on finding the two poles in each piece. The poles always exist in pairs. No matter how small you break the magnet into, even the smallest piece will have the two poles.

Activity- 6 To prove that if a magnet is cut into two or more parts, each part behaves like a complete magnet. Learning outcome: The student will be able to understand that no matter how many times a magnet is cut into parts, each part behaves like a complete magnet, i.e. has a north and a south pole of its own. Materials: 

2 Bar magnets.



Iron Filings.



Magnetic compass.

Procedure:

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1) Dip the bar magnet into iron filings to check where the poles are (as more of iron filings would stick to portion near poles, as poles have maximum magnetic strength in comparison to other parts of the magnet) and then get the magnet cut into two pieces (you may use the school workshop). 2) Now ask the students to bring the two halves of the magnet close to the iron filings. They will observe that more iron filings again get attracted to the two ends of each half than their respective centers. This shows that the two ends of each half, again behave like the poles of a magnet which represent the strongest part of the magnet. 3) Again to prove that the cut out pieces behave like a complete magnet, the students will bring one pole of each of these magnets close to the North Pole of another bar magnet. They will again observe that whereas one end of the cut out magnet gets repelled by the N-pole of the bar magnet, its other end gets attracted by it. Thus the cut-out pieces are again seen to behave like complete magnet. So we conclude that if a magnet is cut into two parts then each part behaves as a complete magnet.

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Worksheet - 3 A.

Put a tick mark on the correct answer from the options given with each statement. 1. A magnet will attract an elastic band/a paper clip/a cork. 2. The ends of the magnet are called the magnetic centre/magnetic points/magnetic poles. 3. Like poles will attract/repel each other. 4. The strength of a magnet is weakest/ strongest in the middle. 5. The magnetic poles are called N and S / N and E / S and W.

B.

Select the correct option. 1. When an iron nail is kept near a magnet a. it is always attracted towards the north pole only. b. it is always attracted towards the south pole only. c. it can be attracted towards both north or south pole. d. it is not attracted at all.

2. The force that pushes two magnets apart is a. magnetic force of attraction. b. magnetic force of repulsion. c. gravitational force of attraction. c. electric force of repulsion.

3. When a magnet is cut into two pieces, there would be, in all, a. four N-poles. b. two N-poles and two S-poles. c. four S-poles. d. one N-pole and three S-poles. 40

4. When the north pole of one magnet is brought near the north pole of another magnet a. they will repel each other b. they will repel first and then attract. c. they will attract each other d. they will attract first and then repel.

5. When the north pole of one magnet is brought near the south pole of another magnet a. they will repel each other. b. they will repel first and then attract. c. they will attract each other. d. they will attract first and then repel.

6. Which of these is likely to be attracted by a magnet? a. Plastic b. Steel c. Wood d. Gold

7. Magnetic Field A magnetic field is the area around a magnet where its magnetic effects can be felt. It is represented by curved or straight lines around the magnet. These lines are known as magnetic field lines. Outside the magnet they seem to go from the North Pole to the South Pole.

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Magnetic field

Activity-7 Observe the magnetic field pattern of a bar magnet using iron filings Learning outcome: The student will be able to observe that a heap of iron fillings, when put on a glass sheet, is kept above a bar magnet, gets arranged in a definite pattern. Materials required:  Bar magnet.  Glass sheet.  Iron Filings. Procedure: 1) A sheet of glass is placed over a bar magnet and the iron filings are then sprinkled on the surface of the glass. 2) The force of the magnet will be felt through the glass and each iron filing becomes a temporary magnet. 42

3) If the glass is now tapped gently, the iron particles will align themselves to show the pattern of the magnetic field surrounding the magnet. 4) The filings form a definite pattern, which is a visible representation of the pattern of the magnetic field.

Observation: The magnetic force is very strong near the poles and weakens as the distance from the poles increases.

Activity 8 To draw magnetic field lines around a bar magnet using a magnetic compass Learning Outcome: The students will be able to draw the magnetic field pattern around a bar magnet by using a magnetic compass. Material required: 

Magnetic compass.



Pencil.



Bar magnet.



A sheet of paper. 43

Procedure: 1. Place the bar magnet on top of the paper. 2. Now put the magnetic compass near to one end of the bar magnet and mark the tip of the needle with pencil. 3. Put the tail of needle at the first mark and again mark the tip of the needle. 4. repeat the step till he reaches to other end of the magnet. 5. repeat above steps for the other side of the magnet.

8.

Attraction and Repulsion between two circular magnets a) Attraction

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b) Repulsion

9.

How to make your own magnet? There are several methods of making magnets. We can make it at our home by stroking a magnetic material again and again in one particular direction. Bring a pin or some iron filings near the magnetic material to check whether it has became a magnet. If not, continue the process for some more time. http://moodle.southwell.school.nz/file.php/1165/Magnet/make_a_magnet.jpg

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Activity – 9 To make a magnet of an iron needle. Learning outcome: The students will be able to learn a simple method of making an iron needle into a magnet.

We can make our own magnet from a needle. Needles are made of steel, which is mostly an alloy of iron. 1. Hold the eye of the needle (the end of the needle that has hole). Make sure you hold it carefully so you don't prick yourself.

2. Stroke the needle along one end of a magnet. Move along the magnet in only one direction: from the eye of the needle to the point, not back and forth. Do this twenty to thirty times.

3. Touch the end of the needle to a tag, a paper clip, or another needle. Your needle is likely to lift them up. You have made a magnet.

4. The bigger and stronger a magnet is, the more objects it will pick up at once.

5. If for some reason your needle magnet doesn't work, stroke it again across the magnet a few more times.

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Activity- 10 To make an electro magnet. Learning outcome: The student will be able to understand how a coil of insulated copper wire, wound over an iron needle, starts behaving like a magnet when current is made to flow through it. Materials required: 

Iron nail.



Copper wire.



Battery

Procedure: All you need to do is wrap some insulated copper wire around an iron nail. If you attach a battery to the wire, an electric current will begin to flow and the iron nail will become a magnet. When the battery is disconnected, the iron nail will lose its magnetic property. This application is used in electric bell as in your home and school; very strong electromagnets are used in industry to lift heavy pieces of magnetic metals.

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10.

Demagnetising The magnetism of a magnet can be destroyed by; 1.

Hammering it quickly again and again.

2. Heating a piece of magnetized iron or steel strongly in a flame.

3. Rubbing the magnet by another magnet, in opposite direction to that used for magnetising it, can demagnetise a magnet.

11.

How to keep magnet safe? Magnets lose their magnetism if not properly stored. They should be stored in pairs in a wooden box, with unlike poles on the same side. They must be separated by a piece of wood, while two pieces of soft iron should be placed across their ends.

These pieces of soft iron are commonly called magnetic

keepers.

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Magnetic keepers

Formative Assessment Q1. What happens when a magnet is heated strongly in a flame? Q2. State any two properties of a bar magnet. Q3. A long bar magnet is broken into four unequal pieces. How many individual magnets are formed? Q4. Fill in the blanks: a) A _____________ is the space around a magnet where its magnetic influence can be experienced. b) _________ are the strongest parts of a magnet. c) A magnetic compass always points towards ___________________. d) Unlike poles ________ each other. e) An iron needle can be converted into a magnet by______________. Q5. Write down as many places/situation/devices as you can think of where magnets are used. You can draw pictures as well as write in words.

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Activity-11 Testing the strength of the given magnets Learning outcome: The student will be able to understand a simple method of estimating the strength of a given magnet. Materials required: 1. Two boxes of paperclips (all of same size). 2. Bar magnets. 3. Horseshoe magnets. 4. Some iron filings 5. Plane sheet of paper. Procedure: 1. Ask the children how strong or weak magnets are? Do magnets have different strengths? If so, what makes one magnet stronger than the other? 2. Divide students into groups of 2 each. 3. Supply each group with a handful of paperclips, 1 bar magnet , 1 horseshoe magnet and one sheet. 4. Ask the children to test the strength of the magnets by picking up as many paperclips (as it can), with one magnet and writing that number down. Then do the same for the other magnet. More the paperclips lifted, more will be the strength. 5. Once they complete the task, they can be asked to find other ways to test the strength of magnets. They may use what they already have done (using iron filings 50

and examining the concentration of field pattern near the poles. More the concentration of iron filings, more strong is the magnet.)

Activity-12 Testing two different magnets to find out which one is stronger? Learning outcome: The student will be able to understand a simple method of comparing the strength of two different magnets. Materials required: 

two different magnets.



a ruler which has mm- marking on it.



a paper clip or a pin.



a flat table top.

Procedure: 1.

Place the clip near the pole of the magnet. You will find that the clip is attracted towards the magnet.

2.

Gradually start increasing the distance between the clip and the pole. Note down the observation.

3.

Find a point beyond which there is no attraction. Record this distance. 51

4.

Repeat the same with other magnet.

5.

The magnet that shows attraction over a larger distance is the stronger one.

Activity-13 Making an iron paper clip to float in the air Learning outcome: The student will be able to learn using a magnet to make a paper clip (iron) float in air. Materials required: • Thread. • Bar Magnet, horseshoe magnet and a ring magnet. • Scissors. • Iron Paper Clip. • Scotch Tape. • Glue (optional). Procedure: 1. Take a 10 cm long thread. 2. Attach one end of the thread to the paper clip. 3. Tape the other end of the thread to the teacher’s table. 4. Ask one of the students to hold a bar magnet little above the paper clip. 5. The students will immediately notice that the clip will rise in air. 6. Ask the student to move the magnet slowly and gradually away from the pin to a distance at which the pin doesn’t float in air. 52

7. Ask the student to measure this distance. 8. Repeat the same with the horseshoe magnet and the ring magnet. 9. Ask the students again to measure this distance. Observation table: Magnet

Distance up to which the pin rises up

Bar magnet

Horse shoe magnet

Ring magnet

Conclusion: The distance will depend on how strong the magnet is. More the distance up to which the pin rises stronger is the magnet. 10.

Use of magnets: i)

School Experiments Children can learn about magnetic properties, by conducting experiments with bar magnets. Bar magnets are commonly used because of their low cost, convenient size and ease of use.

ii)

Magnetise Objects Bar magnets can be used to magnetise other objects. We can magnetise a paperclip by stroking it against the bar magnet several times in one direction. We test it by bringing an iron nail close to the paperclip. 53

(A magnetic instrument holder) iii) Industry Industries use bar magnets for automation and the collection of loose metal materials. Bar magnets are also used to help other magnets retain their magnetism.

(An electromagnetic lifter used to lift loose iron particles in metallurgical industry) iv)

Compass When a bar magnet is suspended, such as from a string, it will naturally align itself along the north-south direction. It is this property, which is put to use in a compass.

v)

Removing useful material from wastes Strong magnetic machines are used to separate iron wastes from industrial scarp. 54

http://www.alibaba.com/productgs/360404268/MW5_Series_Electromagnetic_Lifter_for_Handling.html

http://www.sciencephoto.com/media/356717/enlarge

Activities for Students: 1.

(10 minutes) 

Get students to propose how they would test the objects for magnetic behaviour.



Return the magnets and let the students test the objects and record the results in their worksheets.



Analyse the results of the magnetism test. What do all the magnetic objects have in common? (They are made of metals that usually contain iron.)

2.

(15 minutes) 

How can you turn an iron-containing object into a magnet?



Have students take a small nail from the material bag and show them how to stroke the nail with the permanent magnet (use two magnets together if 55

your magnets are fairly weak). How can they prove that the nail is now magnetised? (Let them propose methods such as having the nail pick up paper clips.) 

Can this be demagnetised ? (Yes, by heating or by dropping several times or by hammering.)

3.

(5 minutes ) 

How can we determine which end of the magnet is the N or S pole?



If using a compass or known magnet is suggested, ask students to consider the case when neither of these items was available.



Lead them to the solution of suspending their nail with a string and seeing how it hangs (they now have a compass).



Suspend one group’s magnetised nail with the suspension setup as a demonstration to illustrate how the N and S ends of the nail can be determined.

Summary 

A magnet attracts iron, nickel, cobalt and alloys of these metals.



All magnets have a North-seeking (N) pole and a South-seeking (S) pole.



When magnets are placed near each other, opposite poles attract and similar poles repel each other.



Magnets are found in many of our electrical appliances.



Magnetite is a natural magnet.



A freely suspended magnet always aligns in the geographic North-South direction.

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Summative Assessment PART A Instruction: Mark the correct options1.

Which of these objects would be attracted by a magnet? a) A leather purse. b) A steel key. c) A wooden ruler. d) A plastic bag.

2.

S-pole of Magnet A can hold three steel paperclips and N-pole of Magnet B can hold five. How many clips will the N-pole of magnet A and the S-pole of magnet B hold? a) 5 and 3. b) 3 and 5. c) both 3. d) both 5.

3.

Two objects repel each other when brought close to one another. What is one possible explanation for this? a) Both the objects are magnets. b) One is a magnet and other is a steel. c) Both are made from steel. d) One is a magnet; the other can be a steel piece or a magnet.

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4.

The attraction or repulsion force of a magnet is a) strongest in the middle of the magnet b) strongest at the ends of the magnet c) the same all the way through the magnet d) strongest at only one end of the magnet

5.

Which pair of metals will be attracted by a magnet? a) Iron and nickel b) Gold and silver c) Aluminium and lead d) Iron and aluminium.

6.

Two objects attract each other when are brought close to one another. Which of the following is not a possible explanation for this? a) both the obects are magnets. b) one is a magnet and other is a steel. c) both are steel. d) one is a magnet, other can be a steel or a magnet.

7.

Demagnetising of a magnet can be done a) only by hammering it. b) only by heating it. c) only by rubbing this magnet by another magnet in a direction opposite to that used for magnetizing it. d) by all of the above methods. 58

8.

Which of the following is not likely to be among the practical uses of a magnet? a) to know the directions at a place. b) to separate magnetic and non-magnetic materials. c) to cool a bar of aluminium. d) to magnetise a bar of iron.

9.

When a permanent magnet (SN) is placed close to a bar of soft iron (PQ), what is likely to happen?

a) The end P of the iron bar becomes a north pole. b) The end P of the iron bar becomes a south pole. c) The bar PQ does not get magnetised at all. d) The N and the S poles of the magnet would get reversed.

10.) A magnet is kept in touch with two pieces of iron as shown.

The likely arrangement, of the induced poles, in the two pieces of iron, is

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PART B Answer the following questions1. How can you decide whether an object is magnetic or not?

2. Which of these objects are magnetic and which are non-magnetic? wooden pencil, nail, plastic spoon, piece of paper, metal spoon, rubber, coin

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PART C In the two pairs of magnets shown below mention with reason(s), which pair of magnets will attract each other and which one will repel each other.

(A)

(B)

PART D Fill in the blanks using the words given below Magnetic __________ are substances that are ___________ to magnets. They can also be used to make magnets. Very few materials are ___________. Iron and __________ are magnetic materials.

Attracted

magnetic

steel

materials

Recapitulation: Applicative skills Let us see what have we understood about Magnets! Question 1: Show the general nature of the magnetic field pattern of a bar magnet.

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Question 2: There are two poles of a Magnet: "North" and "South". How are these poles defined? Explain how we can experimentally determine which end of a magnet is its "North" and which is its "South" pole end? Question 3: A mechanic visits you one day, carrying a large wrench. She says the wrench got magnetised after setting it near a magnet. Now the wrench has become a problem, because it has started attracting all the other tools in her toolbox. Can you think of a way to demagnetise the wrench for her?

Monika with a wrench

Activity: Hands on Proof

Find different types of magnets and bring it with you to class for discussion. Collect as much information as you can about your magnet prior to discussion: •

Location of poles.

•

Deciding which pole is North, and which pole is South.

•

Type (metal).

•

Shape. 62

Vocabulary Building Bar magnet - a magnet, usually of hard steel, shaped as a rectangular bar and has its two poles at its two ends. magnetic repulsion - the force by which two magnets push each other apart magnetic attraction - the force by which two magnets are pulled towards each other magnetic force - the attracting or repelling force between two magnets or a magnet and a magnetic material. magnetic field - a region around a magnet where its magnetic force/effects can be felt. magnetic poles - The two ends of a magnet, where there is maximum magnetic force/maximum strength of the magnet. north pole - that end of a bar magnet which always points towards geographic north when the magnet is suspended freely. south pole - that end of a bar magnet which always points towards geographic south when the magnet is suspended freely.

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Acknowledgement Suggested Video Clips/Web Links/ Powerpoint

Name

Title of Video Clips/Web Links/ PowerPoint

Video Link 1

http://www.youtube.com/watch?v=G-nkIECIBWM

Video Link 2

http://www.youtube.com/watch?v=8Y4JSp5U82I&feature=related

Video Link 3

http://www.youtube.com/watch?v=uj0DFDfQajw&feature=channel

Web Link 1

Powerpoint 1

Powerpoint 2

Web link 2

http://www.engineeringinteract.org/resources/parkworldplot/flash /concepts/magneticforces.htm Magnet and Force http://www.primaryresources.co.uk/science/powerpoint/magnets_ and_springs_WWtbaM.ppt http://www.primaryresources.co.uk/science/powerpoint/intro_to_ Magnet and Springs magnets.ppt #257 http://www.bbc.co.uk/schools/scienceclips/ages/7_8/magnets_spri ngs.shtml

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Resources 

http://www.tutorvista.com/content/physics/physics-iii/physics



http://www.practicalphysics.org/go/Default.html



http://lgfl.skoool.co.uk/content/keystage3/Physics



http://www.sasked.gov.sk.ca/docs/physics/u220phy.html



www.wikipedia.com



www.answer.com



www.brainpop.com



www.trachersnet.com



Library.thinkquest.org



http://www.school-for-champions.com/science/magnetism.htm



moodle.southwell.school.nz/.../view.php?id=16415



Answers to Readers' Questions



neticforces.hhttp://www.engineeringinteract.org/resources/parkworldplot/flash/tests/ questions/magtm



http://www.primaryresources.co.uk/science/science4b.htm#magnets

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Rubric: Assessment for Learning Parameter Learner is able to:

Beginning (1)

Partially Proficient (2)

Identifying various types of magnets.

Differentiate between magnetic and non-magnetic materials with an illustration.

Identifying the poles of a given magnet. Magnetic compass and its uses.

Identifying the strength of a magnet.

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Proficient (3)

Exemplary (4)

CENTRAL BOARD OF SECONDARY EDUCATION Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India