Handbook p2 magnetism

Agastya International Foundation

Magnetism Handbook P2

“Reason, Observation and Experience; the holy trinity of science.�

- Robert Green Ingersoll (1833-1899)

2

HANDBOOK – P2 MAGNETISM OVERVIEW OF HANDBOOK ABL

Concept

No of Activities

ABL1 ABL2 TOTAL

Magnets Properties of Magnets

3 4 7+1

ABLs WITH REFERENCE TO STANDARD S.No. 1 2

STANDARD 6 6

RELEVANT ABL ABL 1 ABL 2

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Time (Min) 55 50 120

Page No. 3 11

3

LIST OF FIGURES, CHARTS AND WORKSHEETS S. No Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Worksheet 1

Name Magnetic Molecule Alignment of a Piece of Iron and a Magnet Bar Magnet Bar magnet cross-section Magnetic lines of force Magnetic field around a Magnet Types of Magnets Magnets and their properties

Page No 5 8 8 14 15 18 20

Note to Instructor: All the figures in this handbook are for the Instructor’s reference only. The Charts need to be printed and shown to the learners during the course of the activity. Worksheets need to be printed out in advance for the learners. The number of worksheets required is mentioned in the Material List.

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4

ABL 1: Magnets Activity

Learning Objective

Key Message 

1.1

What is a magnet?





Time

A magnet is a material or 25 Min object that attracts magnetic materials.

A magnet can be made only from a magnetic material.

There are two magnetic poles, north pole and south pole.

1.2

What are magnetic poles?

1.3

How to make an  Magnetic materials can be artificial magnet and changed into artificial magnets. what care is taken  Magnets can lose their magnetic while handling property if not handled properly magnets? or and subjected to heat and mechanical stress.

Total

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10 Min

20 Min

55 Min

5

ABL 1.1

Time: 25 min

LEARNING OBJECTIVE:What is a magnet?

ADVANCE PREPARATION Material List S. No. 1 2 3 4 5 6 7 8 9

Material Sand Iron filings China dish Steel pins Pieces of plastic toothpicks Bar magnet Iron rod A 4 size paper Board or flip chart

Numbers Required 100 grams 50 grams 1 per class 10 per class 10 per class 1 per class 1 per class 1 per class 1 per class

Things to do Mix the sand and iron filings in the china dish. Mix the steel pins and plastic toothpicks and place them on an A 4 size paper.

Safety Precautions Iron filings and steel pins can hurt a learner so warn the learners to be careful and also teach them how to handle these objects.

SESSION Link to known information/previous activity Not Applicable Procedure Place all the material on a table and make sure that all the learners can see the activity clearly.

Show the two mixtures, the sand and iron filings and the plastic toothpicks and steel pins, to the learners.

Ask them to identify the contents of the mixtures. Ask one learner to separate the mixture. Ask the learners if there are any other ways to separate the mixtures. Take down all their suggestions on the board or on the flip chart. Then demonstrate the use of magnet to separate the mixtures. Ask another learner to separate the mixtures with the help of an iron rod.

UNDERSTANDING THE ACTIVITY Leading questions 1. What are the contents of the mixture?

2. How did the first learner separate the mixture?

3. What happened when the magnet was brought near the sand-iron filling mixture?

4. What happened when the magnet was brought near the steel pins-plastic toothpicks mixture?

5. What happened when the iron rod was brought near the mixtures?

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Discussion and Explanation  Each of the mixtures has one metallic and one non-metallic component.  It is easier to separate the pins and plastic mixture by hand than the sand and iron filings mixture.

This is because of the size and number of particles in the mixture.  When the magnet was brought near the mixtures, it pulled the iron filings and the steel pins towards itself.  The magnet did not attract the sand and the plastic pieces.  The iron rod did not attract any of the four components in the mixtures. This is because the iron rod does not have the ability to attract anything.  The materials that are attracted by a magnet are called magnetic materials while those that cannot be attracted by a magnet are called non-magnetic materials.  When the magnet was brought neat the sand-iron filling mixture, the iron filings, which are of magnetic material were attracted to the magnet, while the sand was not. Thus they were separated. Similarly, steel pins, which are magnetic, were attracted to the magnet.

KEY MESSAGES  

A magnet is a material or object that attracts magnetic materials.

A magnet can be made only from a magnetic material.

LEARNING CHECK: Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Take a fridge magnet and try to stick it to various surfaces. The magnet will stick to some surfaces while it will not stick to others. Make a list of all the surfaces that were made of magnetic material (the ones that the magnet stuck to) and how may are non-magnetic (the ones that it did not stick to).

INTERESTING INFORMATION How was magnetism discovered?

It is said that, there was a shepherd named Magnets, who lived in ancient Greece. He used to take his herd of sheep and goats to the nearby mountains for grazing. He would take a stick with him to control his herd.

The stick had a small piece of iron attached at one end. One day he was surprised to find that he had to pull hard to free his stick from a rock on the mountainside. It seemed as if the stick was being attracted by the rock. The rock was made of a magnetic material (later named as magnetite) and it attracted the iron tip of the shepherd’s stick. It is said that this is how magnetism was discovered. Magnets are named after the shepherd named Magnes.

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7

Magnetic Molecule Alignment of a Piece of Iron and a Magnet – Figure 1

All atoms have magnetic properties due to the spinning action of the atoms electrons. Groups of atoms join together so that their magnetic fields due to the rotating electrons are in the same direction. Magnetic materials are composed of groups of such tiny molecular magnets at a molecular level. There are several domains in the martial and molecular magnets in dominoes are oriented in one direction. And this direction of orientation is different for different domains.as a result resultant magnetic effect due to magnets in all the dominoes at any point is zero hens by themselves these magnetic materials do not show natural magnetism.

When magnetized by an external magnetic source all the tiny magnets alien along the same direction. The field due to each of these molecular magnets at any point is in the same direction and gets added. This results in the magnetic behavior.

VOCABULARY Magnet: A magnet is a material or object that attracts magnetic materials.

Magnetic material: A material or an object that is attracted by a magnet is called a magnetic material.

E.g., iron, steel

Time: 10 min

ABL 1.2 LEARNING OBJECTIVE: What are Magnetic poles?

ADVANCE PREPARATION Material List S. No. 1 2 3 4 5

Material Bar magnet Thread Vertical stand Magnetic compass Marking pencil

Numbers Required 1 per class 1 per class 1 per class 1 per class 1 per class

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8 Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Do you remember that we saw that the magnet attracted some objects and some were not? Iron filings and steel pins were attracted to the magnet. Today we will see why the magnet attracts these objects.

Procedure Alignment of a freely suspended magnet Take a bar magnet. If the ends are not marked as S and N (for south and north), mark one of its ends with a marking pencil for identification. Place the vertical stand firmly on the table. Now, tie a thread at the middle of the magnet. Tie the other end of the thread to the vertical stand, so that the magnet is suspended. Let it come to rest.

Mark two points on the table to show the position of the ends of the magnet when at rest. Draw a line joining the two points. This line shows the direction in which the magnet was pointing in its position of rest. Also note which end of the magnet is the end that you have marked.

Now, rotate the magnet by gently pushing one end in any direction and let it come to rest. Again, mark the position of the two ends in its position of rest. Repeat it two more times.

Explain how a magnetic compass works, i.e., the needle of the compass will always align itself to the northsouth direction.

Note to Instructor: Explanation should be only for the use of the compass and not it's the principle behind it. The full explanation can be done at some other time when there is no other activity going on.

Information on the working of the compass is given at the end of the activity.

Using a magnetic compass, find the direction of the magnet in rest. At this time the compass and the magnet should be far apart. Otherwise, the needle in the compass will be attracted or repelled by the bar magnet and not give correct result.

Now, bring bar magnet near compass and observe the needle in the compass.

UNDERSTANDING THE ACTIVITY Leading questions 1. When the suspended magnet comes to rest, does its position change?

2. Which direction does the needle of the compass usually point to?

3. Which direction does the magnet come to rest in?

4. What happens when the compass comes close to the magnet? Use the information you had learnt in the previous activity.

Discussion and Explanation  We find that a freely suspended bar magnet always comes to rest in a particular direction. Even if it is rotated any number of times, it will come back to the same position.  The needle of the compass also points at the same direction and this is the North-South direction.

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9 



You will notice that the freely suspended magnet also aligns along the North-South direction. The end of the magnet that points towards North is called its North seeking end or North Pole of the magnet.

The other end that points towards the South is called South seeking end or the South Pole of the magnet. All magnets have two poles, whatever their shape may be. Usually, north (N) and south (S) poles are marked on the magnets.

When you bring bar magnet comes near a compass, the needle of the compass changes its direction. In the latter activities where the magnetic field lines are traced around a bar magnet you will learn that north and south poles are the virtual points at either ends where magnetism is concentrated.

KEY MESSAGES: 

There are two magnetic poles, north pole and south pole.

LEARNING CHECK: Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

INTERESTING INFORMATION: 



A freely suspended magnet always points in the North-South direction even in the absence of any other magnet. This suggests that the Earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle) to point always in a particular direction. The South Pole of the Earth's magnet is in the geographical North because it attracts the North Pole of the suspended magnet and vice versa. Thus, there is a magnetic S-pole near the geographical North, and a magnetic N-pole near the geographical South.

Figure 2 – Bar Magnet If you cut a magnet in half, each of the halves would be a magnet with a north and a south pole. If you cut the halves in half, you would still have magnets with both poles. If you were cutting iron bar, you would eventually end up with a single iron atom, which would still have a north and a south pole, where these tiny magnets line up the opposite poles linked along a chine neutralize each other leaving all north poles at one end and south pole at the opposite end

Figure 3 – Bar magnet cross-section 

Working of a compass: The earth is considered as a huge bar magnet. So it has a North Pole and a South Pole.The Earth's North and South poles are aligned along the geographical South and North Poles respectively.

A compass is an instrument containing a freely suspended magnetic needle in the center of the dial and the directions, i.e., North South East and West are marked on the dial of the compass.As the Earth works as a magnet, the needle of the compass will align itself to the north-south direction of the Earth.

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10

Time: 20 min

ABL 1.3

LEARNING OBJECTIVE: How to make an artificial magnet and what care is taken while handling magnets?

ADVANCE PREPARATION Material List S. No. 1 2 3 4 5 6 7 8 9

Material Bar magnet Thread Steel blade Hammer Candle A piece of thread Vertical stand Magnetic compass Marking pencil

Numbers Required 1 per class 1 per class 1 per class 1 per class 1 per class 1 per class 1 per class 1 per class 1 per class

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Do you remember that there are magnetic materials and non-magnetic materials? Today we will see how we can make a magnetic material into a magnet.

SESSION 1.3a Procedure 1.3a Magnetizing a magnetic material Take a shaving blade and cut in to two pieces along its length. Explain to the learners to be careful of the sharp edges of the blade and show them how to handle the blades. Dip the blades into the dish of iron filings. No filings will stick to the blade. So we can say that the blade is not working as magnet.

Mark one end of the blade. Rub the piece of blade with N-pole of the magnet. Start at the marked end of the blade and lift the magnet clear at the end of each stroke. Repeat this ten times in the same direction.

Now dip it in the dish of iron filings and observe what will happen (the iron filings will be attracted to the blade).

Suspend the blade on a thread (as shown in the activity 1.2) and determine the two poles of the blade.

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UNDERSTANDING THE ACTIVITY Leading questions 1. Why does the blade initially not attract the iron filings?

2. Why does the blade attract the filings after it has been rubbed by a magnet?

3. How does the magnetised blade align when suspended freely?

Discussion and Explanation  The blade is a magnetic material but not a magnet itself. So initially, it did not attract the filings.  When the blade was rubbed by a magnet, it became a magnet and so attracted the filings. 

When the magnetised blade is suspended freely, it will always align along the north-south direction. This blade is a temporary magnet, i.e., it will remain a magnet for a short time.

SESSION 1.3b Procedure 1.3b Loss of magnetic property of a magnet Magnetize two pieces of shaving blade. Check the magnetic property of both the pieces of blade by dipping them into a dish of iron filings and ensuring that they have been magnetized. Take one of the blades and hammer it. Now, bring it near the iron filings. Observe and note what happens.

Take the second piece of magnetized blade. Hold the blade to the flame of the candle. Once it is cool, test its magnetic property by bringing it near the iron filings.

UNDERSTANDING THE ACTIVITY Leading questions 1. How were the blades magnetized?

2. What happened to the blade after it was hammered or heated?

Discussion and Explanation  The blades were magnetized when rubbed by a magnet.  When hammered or heated the blades lose their magnetic property and so do not attract the iron filings. So it is important that the magnets are kept away from heat and are handled carefully and not dropped or hammered. Also, magnets become weak if they are not stored in specific ways designed to prevent their weakening.

KEY MESSAGES:  

Magnetic materials can be changed into artificial magnets.

Magnets can lose their magnetic property if not handled properly or Subjected to heat and mechanical stress.

LEARNING CHECK:

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12 Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Try rubbing the blade with a magnet in both directions, i.e., from end 1 to end 2 and then back to end one. Does this magnetize the blade?

INTERESTING INFORMATION  

To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side.

They must be separated by a piece of wood while two pieces of soft iron should be placed across their ends. For horseshoe magnet, one should keep a piece of iron across the poles.

Keep magnets away from cassettes, mobiles, television, music system, compact disks (CDs) and the computer as strong magnets can alter the magnetic property of materials used in such equipment and interfere with proper functioning.

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13

ABL 2: Properties of Magnets Activity

2.1

Learning Objective How do poles of a magnet interact when brought near poles of other magnets?

2.2

What is a magnetic field?

2.3

Do both the poles of a magnet have the same magnetic pole strength?

2.4

What are the types of magnets?

Key Message

Time



Like poles repel each other while unlike poles 10 min attract each other



Magnetic field of a 20 Min substance is the area around the substance that is influenced by it



Both the poles of a 10 Min magnet have equal pole strength.



Magnets are classified as natural and artificial Artificial magnets can be of different geometrical shapes to suit the requirement.



Total

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25 Min

65 Min

14

Time: 10 min

ABL 2.1 LEARNING OBJECTIVE: How do poles of a magnet interact when brought near poles of other magnets?

ADVANCE PREPARATION Material List S. No 1 2 3

Material Bar magnet (marked) Iron filings A 4 sheet paper

Required Quantity/ Group 2 30 gram 1

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Do you remember that we saw that some objects were attracted by the magnet and some were not? Iron filings and steel pins were attracted to the magnet. Today we will see how the magnets behave when two ends of different magnets are brought close together.

Procedure Hold up the magnets so that the learners can see both the magnets. Show that each end is marked. Place both the magnets on the paper and move the similarly marked ends of the two magnets nearer. Ask the learners to observe how the magnets behave. Now, bring the other two ends of the magnets (again they will be similarly marked). Observe, again, how the magnets behave.

Then, bring the two differently marked ends of the magnets closer. Observe howdo they behave. Turn around the magnets and try the same things with the other ends of the magnets.

UNDERSTANDING THE ACTIVITY Leading questions 1. How are the two ends of the magnet marked?

2. What happened when similarly marked ends of the magnets came closer?

3. What happened when differently marked ends of the magnets came closer?

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Discussion and Explanation  

You will notice that the two ends of the magnet are marked south and north of the two magnets..

When brought together, will move away from each other. So, we can say that similar or 'like' poles repel each other. In the same way, when the other two ends are brought together, they also repel each other.



Now, when differently marked ends (N and S) are brought towards each other, i.e., North Pole of one magnet brought towards the South Pole of the other, they will be pulled towards each other.

We say that they are 'attracted' to each other.

Thus, like poles repel each other while unlike poles attract each other.  A magnet is cherectrised by two poles north and south  Unlike pole attract and like poles reples each other

KEY MESSAGES 

Like poles repel each other while unlike poles attract each other

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

INTERESTING INFORMATION The materials which are attracted towards the magnet (iron cobalt steel etc) are classified as ferromagnetic me trials .thy can be easilymagnetized with the help of an external magnetic source . in fact there are some magnetic menials which are repelled by strong magnets these are diamagneticmaterials. A supper conductor is an example of a perfect diamagnetic they find application in magnetic levitation

ABL 2.2

Time: 20 min

LEARNING OBJECTIVE: What is a magnetic field?

ADVANCE PREPARATION Material List S. No 1 2 3

Material Bar magnet (marked) Iron filings A 4 size chart paper

Required Quantity/ Group 1 per class 30 gram per class 1 per class

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16 Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity We learnt in the previous activity that like poles repel each other and unlike poles attract each other.

Today we will see why the magnet attracts these objects.

Procedure Place the chart paper on top of one of the bar magnets, trace the outline of the bar magnet and mark which end is North and which is South. Now, sprinkle the iron filings uniformly over the paper. Lightly tap the paper a few times. Observe what happens. Mark the design formed by the filings. What do you observe?

UNDERSTANDING THE ACTIVITY Leading questions 1. What happened when the paper was tapped?

2. What happens top the iron filings on the edge of the paper?

Discussion and Explanation  When the paper is tapped, the iron filingsnear the magnet formed a certain pattern on the paper.

This will look like the figure given below.

Figure 4 – Magnetic lines of force Agastya International Foundation. For Internal Circulation only.

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17 

These lines that the iron filings make are called 'magnetic lines of force'. These lines start from the North Pole of the magnet and end at the South Pole of the magnet.



The filings at the edge of the chart paper do not form the pattern but stay where they are. This is because the distance between the magnet and the filingsis large and the influence of the magnet is less.

So the area around the magnet where the magnet can pull the iron filings is called the 'magnetic field' of the magnet. You will observe that there will be more iron filings near the poles. This is because the magnetic lines of force come closer to each other at the two poles than at the centre of the magnet.



KEY MESSAGES 

Magnetic field of a substance is the area around the substance that is influenced by it

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF Take an A4 size paper and place a bar magnet on it. Mark the position of the magnet. Now, take a compass and place it next to the North Pole of the magnet. Mark the position of the north end of the needle of the magnet. Move the compass a little to the centre of the magnet. Now mark the position of the needle.

Move the compass again in the same direction. Repeat these till you come to the South Pole of the magnet. Join all the points that you have marked. What do you observe?

Repeat the same on the other side of the magnet. You will also see the same pattern emerging. The figure will look like the one shown below. The lines that you see are the magnetic lines of force and the area where the lines are drawn is the magnetic field of the magnet.

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18

Figure 5 – Magnetic field around a Magnet

ABL 2.3

Time: 10 min

LEARNING OBJECTIVE: Do both the poles of a magnet have the same magnetic pole strength?

ADVANCE PREPARATION Material List S. No. 1 2

Material Bar magnet Steel Pins

Required Quantity/ Group 1 20

Things to do Not Applicable Safety Precautions Not Applicable

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SESSION Link to known information/previous activity Not Applicable Procedure Take a bar magnet. Bring the steel pins, one by one, towards the North Pole of the magnet. It will be observed that these pins will stick to the magnet. Try to get as many pins attached to the magnet as possible. Take care that they are attached to only one end of the magnet. Count the number of pins that the North Pole of magnet can attract. Remove the pins from the North Pole and repeat the activity with the South Pole. Count the number of pins that are attached to the South Pole.

UNDERSTANDING THE ACTIVITY Leading questions 1. How many pins were attached to the North Pole of the magnet?

2. How many pins were attached to the South Pole of the magnet?

Discussion and Explanation  You will notice that the number of pins attached to each of the poles is the same. By this we can that both the poles have the same power of attraction. This force of attraction is called the magnetic force. So we can say that both the poles of the magnet have the same magnetic force.

Additional information: A bar magnet is strongest at its ends, or poles. The magnetic field can be represented by magnetic field lines, which enter one end of the magnet and exit the other.

For instance, in a bar magnet, the magnetic field lines emerge from the north pole of the magnet and enter the magnet at the South Pole. The magnetic field lines are most closely packed together at the poles,

KEY MESSAGES: 

Both the poles of the magnet have equal pole strength

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation.

TRY IT YOURSELF 

Magnetize a blade. See how many pins the blade can attract. Also see how many pins the magnet that you used to magnetize the blade attracts. Which of them attracts more pins? So which one has more Strength?

Note: Using a blade can be dangerous. This activity should be done under adult supervision.

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20 Time: 25 min

ABL 2.4 LEARNING OBJECTIVE: What are the different types of magnets?

ADVANCE PREPARATION Material List S.No. 1 2 3 4 5 6 7

Material Bar magnet Horse shoe magnet Needle magnet Natural magnet (Lodestone) Shaving blade 2" long Nail Steel pins

Required Quantity/Group 2 per class 1 per class 1 per class 1 per class 1 per class 1 per class 5 per class

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Not Applicable Procedure Put all the material together on the table and ask the learners to separate them. Ask them on what basis did they separate them.

The learners will separate the magnets from the non-magnets. They will be confusedas to which group the lode stone will be a part of,as they will not be sure if it is a magnet or not. Suggest that they check them by seeing if they attract steel pins.

As they had learnt earlier, they will be able to magnetize the nail and blade.

UNDERSTANDING THE ACTIVITY Leading questions 1. Which one of them are magnets?

2. How did you recognize them as magnets?

3. Can you make the shaving blade and nail into magnets?

4. Can you name the different types of magnets you have here according to their shape?

Discussion and Explanation

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21 



Explain to them that there are two main types of magnets - Natural and artificial. Lode stone is natural magnet whereas bar magnet, dick magnet, ring magnet, horse magnetand needle magnet are artificial magnets.

Figure 6 – Types of Magnets Magnets are used in anything with a motor, refrigerator, cabinet latches; computer, tape recorders and video players are some of the large number of uses of the magnet. They are used in industry and scientific researches.

KEY MESSAGES:  

Magnets are classified as natural and artificial.

Artificial magnets can be of differentgeometrical shapes to suit the requirement.

LEARNING CHECK: Material List S.No. 1 2

Material Work sheet 1(given after the end of the activity) Chart paper cut into A 4 size sheets

Required Quantity/Group Same as the number of learners doing the evaluation 10

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Procedure On one chart paper, write North Pole and on the other write South Pole. One chart will be blank. The rest of the charts will have names of materials which are magnetic as well as non-magnetic, eg, iron, stone, paper, water bottle, steel glass, knife, paper clip, eraser, etc.

One learner will become the North Pole and the other will be South Pole (they hold the charts with this written on them). The third learner will become the blank page. Distribute the other papers to the other learners. One by one, the learners have to run to either of the poles, if they are magnetic, or to the blank page, if they are non-magnetic.

This activity will show if they understand about magnetic and non-magnetic materials.

Note to Instructor: This game can be played using actual material like the stone, glass etc.

Once the learners complete the above activity, distribute the worksheets for the learners to do the exercise.

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Work sheet 1 Magnets and their Properties 1. In the bar magnet given below, draw the magnetic lines of force. Remember to put the arrows to show the direction of the flow.

N

S

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ADDITIONAL ACTIVITY

LEARNING OBJECTIVE How do poles of different magnets behave with respect to poles of other magnets?

Note to Instructor: This activity is to be done only after activity 2.2 if there is time remaining.

ADVANCE PREPARATION Material List S. No 1 2 3

Material Bar magnet (marked) Iron filings A 4 size chart paper

Required Quantity/ Group 2 per class 30 gram 1 per class

Things to do Not Applicable Safety Precautions Not Applicable Procedure Draw a straight line on the table. Place the two unlike sides of two magnets facing each other on this line.

Take care to see that they do not get attached to each other. Now place the chart paper on them and mark them. Sprinkle iron filings and give the chart paper a few taps. Observe what happens. Mark the design formed by the filings. Repeat the same activity with like poles facing each other.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you know about like and unlike poles?

2. What happened when the paper was tapped when two unlike poles were facing each other?

3. What happened when the paper was tapped when two like poles were facing each other?

Discussion and Explanation In the first instance, when the paper is tapped, the iron filings will form a certain pattern on the paper. This will look like Fig 1 shown below.

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FIG 1

FIG 2 In the second case, with like poles facing each other, the pattern will like in Fig 2.

This will explain why like poles repel and unlike poles attract each other.

KEY MESSAGES  

Unlike poles attract each other Like poles repel each other

WEB RESOURCES http://www.windows2universe.org/physical_science/magnetism/bar_magnet_interactive.html http://www.engineeringinteract.org/resources/parkworldplot/flash/concepts/magneticforces.htm http://my.execpc.com/~rhoadley/magindex.htm http://www.youtube.com/watch?v=fghLhJe1JLY

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