Handbook p4 light

Agastya International Foundation

Light Handbook P4

“There is a single light of Science, and to brighten it anywhere is to brighten it everywhere.�

-Isaac Asimov (1920-1992)

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Handbook – P4 Light OVERVIEW OF THE HANDBOOK ABL

CONCEPT

ABL 1 ABL 2 ABL 3 ABL 4 ABL 5 ABL 6

Nature and Properties of Light Formation of Shadows and Eclipses Reflection of light by plane mirrors Regular and irregular reflection Reflection of light by spherical mirror Image formation in concave mirrors

No. of ACTIVITIES 6 5 3 2 5 2

TIME (min) 70 60 60 40 65 55

ABLs WITH REFERENCE TO STANDARD S.No. 1 2 3

STANDARD 5, 6, 7 6, 7 8, 9, 10

RELEVANT ABL ABL 1 and ABL 2 ABL 3 and ABL 4 ABL 5 and ABL 6

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PAGE No. 4 20 34 44 51 65

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LIST OF FIGURES, CHARTS AND WORKSHEETS

S. No

Name

Page No

Figure 1

Convergence of sunrays at a point

7

Figure 2

Light travels in a straight line

10

Figure 3

Formation of image when light travels through a pinhole

12

Figure 4

Activity showing the passage of light

17

Figure 5

Lateral image formed by a Plane Mirror

38

Figure 6

Diagram showing the reflection of light from a Plane Mirror

43

Figure 7

Reflection of rays from rough and smooth surfaces

46

Figure 8

Reflection form uneven surface

46

Figure 9

Diagram showing the incident and reflected rays

48

Figure 10

Reflected rays seem to meet at a point beyond the mirror

49

Figure 11

Reference table – position of Image and object

66

Chart 1

Path of parallel rays after they pass through the magnifying glass

7

Chart 2

Change of size of image with change in distance of the object from pinhole

13

Chart 3

Umbra and Penumbra of a shadow

24

Chart 4

Solar Eclipse

26

Chart 5

Stages of Lunar eclipse

29

Chart 6

Formation of spherical mirrors

56

Chart 7

Parts of the spherical mirror

57

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Chart 8

Reflection of parallel beam of rays in a concave mirror

58

Chart 9

Reflection of parallel beam of rays in a convex mirror

58

Chart 10

Parts of a concave mirror

62

Chart 11

Position of the image in a concave mirror when the object is beyond C

63

Chart 12

Formation of the image in a convex mirror

63

Chart 13

Formation of the image when object is beyond C

70

Chart 14

Formation of the image when object is at C

70

Chart 15

Formation of the image when object is between F and C

71

Chart 16

Formation of the image when object is at F

71

Chart 17

Formation of the image when object is between F and P of the mirror

72

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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ABL1: NATURE AND PROPERTIES OF LIGHT

Activity

Learning Objective

Key Message 

1.2

How do we see things around us?

What is light?



Light is essential to see objects around us Light is a form of energy

1.3

How does light travel?



Light travels in a straight line



The size of the image is inversely proportional to the distance between the object and the pinhole. i.e., lesser the distance between the object and the pinhole, larger is the image and vice versa.

Objects absorb energy from the light.

The bouncing of light from any surface is called reflection Since the total energy is always conserved, Incident light energy = reflected light energy + light energy absorbed in the slab + transmitted light energy.

A material which allows most of the light to pass through it is called a transparent material.

A material that allows only a part of light to pass through it is called a translucent material.

A material that does not allow any light to pass through it is called an opaque material.

TOTAL

1.1

1.4

What is the principle of a pinhole camera?

  1.5

What happens when light interacts with matter?





1.6

Do all objects allow light to pass through them?

 

6 Activities

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Time 10 min 10min 10 min 15 min

10min

15 min

70 min

6

ABL 1.1

Time: 10 min

LEARNING OBJECTIVE: How do we see the things around us?

ADVANCE PREPARATION Material List A dark room. If dark room not possible, cover the teacher’s table with a thick cloth so that the space under the table becomes dark. Place a few objects in this dark space like a bag, stool, etc. A torch.

Things to do Not Applicable Safety Precautions Do not keep anything that can harm the learners in this dark area.

SESSION Link to known information/previous activity Not Applicable Procedure Take the learners to the dark room/area. Ask them to go in or peep in and report back what they see. Then ask them to use a torch and see what is in the room/area and report back what they can see.

Note to Instructor: If the experiment is being shown under the table, divide the learner into groups so that all of them will get a correct grasp of what is being taught.

UNDERSTANDING THE ACTIVITY Leading questions 1. What did you see the first time you went into the dark room?

2. What do you think is kept in this room?

3. What did you see when you went into the room again with the torch?

4. Why can you see the objects in the room now?

Discussion and Explanation The first time you went into the room, you could not see anything. You had no idea what was kept in the room. The next time, when you went with the torch, you could see what was kept in the room. Initially Agastya International Foundation. For Internal Circulation only.

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nothing could be seen because the objects kept in the room do not give out light. Only when the light from the torch fell on the objects, they could be seen.

Similarly, when the light of the Sun falls on the objects, we see them. At night, when there is no sunlight, we cannot see anything. So to see objects at night, we put on the light or light a candle. The light from the light or candle falls on the objects and we can see them.

ADDITIONAL INFORMATION The torch emits light. Any object that emits light is called the source of light. The sun, candle, bulb, firefly, stars are all sources of light. They are called self-luminous objects. Objects that do not emit their own light are called non-luminous objects, e.g., chair, books, wood, etc. You can see luminous objects while you cannot see non-luminous objects till light from other source falls on them.

KEY MESSAGE: 

Light is essential to see the objects around us.

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 You might say that we can see at night without light. Look around think how or why you can see the objects.

This is because light from some source is falling on these objects. You can also see clearly on a moonlit night.

This is because the Moon is reflecting the sunlight that falls on it.

VOCABULARY  

Self-luminous objects: Objects that emit light are called self-luminous objects.

Luminous objects:Objects that do not emit their own light but appear bright because of light incident on them.

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ABL 1.2

Time: 10 min

LEARNING OBJECTIVE: What is light?

ADVANCE PREPARATION Material List S. No. 1 2

Material Magnifying glass Paper

Required Quantity per group 1 per class 1 per class

Things to do This experiment has to be conducted in the open where there is bright sunshine. So take permission to take the learners out. Conduct this only if there is bright sunshine available. It is important that the instructor try this experiment a couple of times before he/she shows it to the learners.

Safety Precautions The rays of the sun, converge to burn the paper, are very strong. So keep the learners at a distance and do not allow them to touch the magnifying glass or the paper.

SESSION Link to known information/previous activity Not Applicable Procedure Take the learners out into the sunlight and get them to sit in a circle. Place the paper on the ground in the center of the circle. Hold the magnifying glass over the paper and move it towards or away from the paper till a bright spot appears on the paper. Hold the magnifying glass at the position.

UNDERSTANDING THE ACTIVITY Leading questions 1. What was the magnifying glass facing?

2. Why do you see a bright spot on the paper?

3. Why does the paper burn only at the bright spot?

Discussion and Explanation The magnifying glass is facing the sun. So the sunrays enter the magnifying glass will meet at a point on the other side of the glass. This point is on the paper and looks bright. At this place where the rays meet, atoms or molecules causing excitation of electron to higher energy levels absorb the light. These atoms during deexcitation produce heat radiation. If the radiation is intense the heat generated may be sufficient to burn the Agastya International Foundation. For Internal Circulation only.

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paper. But, we know that to burn, heat is required. So we can say that the sunlight has heat. Heat is energy.

So we can say that light is a form of energy.

Fig: 1. Convergence of sunrays at a point

Chart 1 - Path of parallel rays after they pass through the magnifying glass

In Chart 1, you will see that the rays from the sun, which are parallel to each other, change their path after they pass through the magnifying glass and meet at a point. The energy that each ray has is added up at this point where they meet. So this point becomes very hot.

KEY MESSAGE: 

Light is a form of energy.

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.

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Additional information for Classes IX and X Q1. What is light?

Light is a form of energy, which enables us to see objects. It interacts as a particle and travels as a wave.

Q2. Like air and water, does light also have mass and can light occupy space?

Like air and water, light is a prerequisite for life on earth. Air and water occupy space and have mass. So, both are matter. Light neither occupies space nor has mass. So it cannot be called matter.

Additional information for Classes IX and X* The theories listed below are only a few of the numerous theories created by many different scientists to explain the nature of light. These four theories are the major and most known theories of the vast collection of theories about the nature of light.

The Corpuscular Theory  Proposed in the seventeenth century by Sir Isaac Newton  States that light emitted by luminous objects consists of tiny particles of matter called corpuscles.

When corpuscles hit a surface, each particle is reflected.  This theory predicts that light traveling from air into water will increase in speed.

The Wave Theory  Proposed by Christian Huygens, a Dutch scientist, in the seventeenth century.  States that light is emitted in a series of waves that spread out from a light source in all directions.

These waves are not affected by gravity.  He disagreed with Newton and said that light traveling from air to water will decrease the speed, and vice versa. Huygens was proved later to be correct.  100 years later, Englishman Thomas Young completely disproved the corpuscular theory by showing that light waves can interfere with each other.

The Electromagnetic Theory  Proposed in the nineteenth century by James Maxwell  Proposed that light waves do not require a medium for transmission.  Light waves possess electrical and magnetic properties and can even travel though vacuum. Light waves are a part of a larger family of electromagnetic waves and make up the electromagnetic spectrum.

The Quantum Theory  Proposed by Max Planck, German scientist in 1900  Stated that light waves travel as separate packets of energy called quanta or photons.  Quantum theory in a way supports corpuscular theory with ‘Quantum’ replacing ‘corpuscles’.

Dual Nature  It is now established beyond doubt that light (for that any radiant energy) exhibits both ‘particle’ and ‘wave’ nature i.e. duality *http://www.angelfire.com/sc3/light/theories.htm Agastya International Foundation. For Internal Circulation only.

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11 Time: 10 min

ABL 1.3 LEARNING OBJECTIVE: How does light travel?

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

Material Candle Thread A 4 size Card Board sheets Match box Stands to hold cardboard sheets

Required Quantity per group 1 per class 1 per class 3 per class 1 per class 3 per class

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity You have observed that luminous objects produce light. How does this light travel?

Procedure This activity can be done in groups, with 6 to 8 learners to every group.

Take three cardboard sheets of equal size. Place them together and make a hole at the centre. Fix these cardboard sheets to the stands and place them on the table. Pass the thread through the holes of three cardboard sheets and adjust the cardboard sheets such that the thread is in a straight line. Remove the thread. Light the candle and place it on one side of the cardboards. Now look through the hole from the opposite side. Observe what you see through the holes. Move the first cardboard slightly to the left. Now try and see the candle flame from the third cardboard. Bring the cardboard to its original position. Try to observe the flame. Repeat the same thing by moving the other two cardboards, one by one.

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UNDERSTANDING THE ACTIVITY Leading questions 1. Initially, can you see the flame of the candle?

2. Can you see the flame when the first cardboard is moved?

3. Can you see the flame of the candle when the first cardboard is brought back to its former position?

4. What happens when the middle cardboard is moved?

5. Can you see the flame after the cardboards are put back into their initial positions?

Discussion and Explanation When the holes in the cardboards are in a line (which we ensured while using the thread) the flame could be seen from the other side. Whenever any of the cardboards were displaced, the candle could not be seen. Only when the cardboards are so aligned, that all the three holes are in a straight line, the flame of the candle can be seen. So we say that light travels in a straight line.

Fig 2: Light travels in a straight line

KEY MESSAGE: 

Light travels in a straight line.

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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 Generally you might have seen that, beams of light from the headlights of cars, bikes, buses, trucks and engines go in straight line into the darkness of night. Similarly when the air in the room is dusty, we can see a straight beam of sunlight entering the room through a narrow hole.

Time: 15 min

ABL 1.4 LEARNING OBJECTIVE: What is the principle of a pinhole camera?

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

Material Candle Card board box Butter paper Fevicol (adhesive) Black chart paper Needle

Required Quantity per group 1 per class 2 per class 1 sheet 1 per class 1 sheet 1 per class

Things to do Cut one side of the cardboard box and cover it neatly with butter paper. Cover the other sides of the box with black chart paper.Prepare charts on the ray diagrams showing the size and position of object. Keep both these things ready before the class begins.

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Safety Precautions Take care to handle the lighted candle as it can cause fire.

SESSION Link to known information/previous activity We have learnt that light travels in a straight line. Here we will see some more examples of this.

Procedure This activity can be done in groups of 6-10 learners to a group.

1.4 a. Show the box to the group and explain that the box is covered with black paper to stop any light from entering the box. The butter paper covered side works as a screen. Make a small hole (pinhole) in the middle of the surface opposite to that of the butter paper. Light the candle and keep it close to the pinhole of the box.

Observe the butter paper surface of the box.

Now, move the candle closer and away from the box. Observe the size of the image.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you see on the butter paper?

2. How is the image?

3. When the candle is moved towards and away from the box, what do you observe?

Discussion and Explanation The rays of light from the flame of the candle enter the pinhole and fall on the butter paper, which acts as a screen. The butter paper catches the light rays and forms the image. You will observe that the image formed on the butter paper is inverted, i.e., upside down. This can be shown as in the figure below.

Fig 3: Formation of image when light travels through a pinhole

The size of the image decreases when the candle is moved away and the size increases when the candle is moved towards the pinhole.

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Chart 2: Change of size of image with change in distance of the object from pinhole

KEY MESSAGE: 

The size of the image is inversely proportional to the distance between the object and the pinhole. i.e., lesser the distance between the object and the pinhole, larger is the image and vice versa.

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.

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16 Time: 10 min

ABL 1.5

LEARNING OBJECTIVE: What happens when light interacts with matter?

ADVANCE PREPARATION Material List

S. No.

Material

1 2 3

Glass slab Laser White paper A4 sheet/ White chart paper Bell pin Drawing board/Thermocol board

3 4

Required Quantity per group 1 per class 1 per class 1 per class 1 per class 1 per class

Things to do Spread the white paper/ chart on the drawing board and fix it with bell pins Safety Precautions Not Applicable

SESSION Procedure Place the glass slab on the drawing board and mark its boundaries. Shine the laser light beam on one face of the slab obliquely. Make sure the laser beam grazes the white paper. Observe the incident ray, the ray emerging from the other face and also the transmitted ray, which will be very faint.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you observe when the light is incident on the one face of the slab?

2. Why does the slab allow the light beam to pass through?

3. Are the incident and the transmitted beams of the same intensity?

Discussion and Explanation  When the light is incident on the one face of the slab, some of the light is reflected while most of it passes through the slab and transmitted through the other side.

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  

The slab is made up of a material like glass, which is transparent to light. A transparent material allows most of the light incident on it to pass through.

The transmitted beam is usually of smaller intensity than the intensity of the incident beam.

When light is incident on the slab there is reflection at the first face, some absorption when it passes through the slab and the remaining light is transmitted.

Incident light energy = reflected light energy + light energy absorbed in the slab + transmitted light energy.

KEY MESSAGES   

Objects absorb energy from the light.

The bouncing of light from any surface is called reflection Since the total energy is always conserved, Incident light energy = reflected light energy + light energy absorbed in the slab + transmitted light energy.

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 warm feeling or high temperature indicates the presence of heat energy, and this energy came from the photons of light.

Heat energy corresponds to the microscopic vibrations of molecules in the rocks.

Temperature measures how large these vibrations are. It takes energy to make these vibrations. Hence, the higher the temperature, the more heat energy an object has.

Heat cannot be seen - people didn't understand what it was for many centuries. As it is an important form of energy, our bodies have evolved special touch sensors to detect it.

Although light can travel through a vacuum, it cannot travel through all objects. When light strikes an object, it can be transmitted, reflected or absorbed. The object is made of molecules, and each molecule has electrons, capable of jumping to higher energy levels by absorbing energy. Light passing through an object is called transmitted light. A light packet has a certain amount of energy in it according to its frequency-- the higher the frequency, the more energy. If this energy corresponds to one of the electron energy levels, the electron will absorb it and re-emit it as heat. Transparent materials, however, do not absorb the energy of the photon. Since the photon is not absorbed, it is able to pass straight through.

Some materials are partially transparent, absorbing some photons and transmitting others. This will make the material look tinted, since it only passes certain colours of light.

VOCABULARY 

Reflection: The bouncing of light from any surface is called reflection.

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

Refraction: The bending of light rays when they travel from one medium to another is called refraction.

ABL 1.6

Time: 15 mins

LEARNING OBJECTIVE: Do all objects allow light to pass through them?

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

Material Torch Torch stand Spoon Clear glass piece Frosted glass Wooden piece

Required Quantity per group 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 From the previous activity you have learnt that, light after interaction with the matter, either gets reflected, absorbed or transmitted. Thus, a material or object can be classified as opaque, transparent, or translucent objects. Let us see in detail what it actually means.

Procedure This activity can be done in groups with 6-10 learners to a group.

Place a torch on a stand and keep a screen at some distance from torch. Take a spoon and place it in-between the torch and screen. Repeat this with a transparent glass piece. Now hold the frosted glass in-between the torch and screen. Take a wooden piece and hold it between the torch and screen.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you see when there is nothing between the torch and the screen?

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2.

3.

4.

5.

What do you observe when a spoon is kept between the torch and the screen?

What do you see when a clear glass is kept between the torch and the screen?

What do you observe when a frosted glass is kept between the torch and the screen?

What do you observe when a piece of wood is kept between the torch and the screen?

Fig 4: Activity showing the passage of light

Discussion and Explanation 1. When there is nothing between the torch and the screen, the screen is brightly lit up with the light of the torch falling on the screen.

2. When a spoon is kept between the torch and the screen, a shadow of the spoon is seen on the screen.

This is because the spoon does not allow the light rays to pass through it and hit the screen.

Substances that do not allow light to pass through them are called opaque objects.

3. When a clear glass is inserted between the torch and the screen, the screen is completely lit up. This is because most of the rays of light from the torch pass through this glass piece and hit the screen.

Objects that allow almost all rays of light to pass through them are called transparent objects. (Note: If an object allows light to pass through it completely, then it will not be visible.)

4. When a frosted glass is kept between the torch and the screen, the screen is illuminated but to a lesser degree. So we can say that only some rays of light pass through the frosted glass. Such substances, that allow only some rays of light to pass through, are called transparent substances.

5. When a piece of wood is kept between the torch and the screen, it forms a shadow on the screen. If the wooden piece is bigger than the screen, the screen will be completely dark. This is because the wooden piece does not allow any ray of light to pass through it. Like the spoon, the wooden piece is also an opaque object.

KEY MESSAGES 

A material which allows most of the light to pass through it is called a transparent material.

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 

A material that allows only a part of light to pass through it is called a translucent material.

A material that does not allow any light to pass through it is called an opaque material.

LEARNING CHECK These questions will help the learners to recollect what they have learnt in this set of activities.

1. Why can you not see a light bulb in a dark room when it is not switched on but it can be seen when it is switched on?

2. Name a natural and an artificial source of light.

3. You can see a volcano lava flow down a mountain even at night. Why? 4. Clothes dry faster in the sun than in the shade. Why? 5. Is water transparent, translucent or opaque?

TRY IT YOURSELF You can check out the objects in your school bags or in the classroom to see if they are opaque, transparent or translucent. Take the objects into the sun and see if they make a shadow, or allow some or all light pass through them.

VOCABULARY:   

Transparent material:A material which allows most of the light to pass through it is called a transparent material.

Translucent material:A material that allows only a part of light to pass through it is called a translucent material.

Opaque material: A material that does not allow any light to pass through it is called an opaque material.

WEB RESOURCES http://www.physics4kids.com/files/light_intro.html http://www.physicsclassroom.com/class/refln

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ABL 2: FORMATION OF SHADOWS AND ECLIPSES

Activity

Learning Objective

Key Message  

2.1

How are formed?

shadows



 2.2

What are Umbra and Penumbra?

2.3

How does a solar eclipse occur?

2.4

How does a lunar eclipse occur?

 

 

2.5

What are the applications of shadows?

5 ACTIVITIES

Time

Shadows are formed by opaque objects in the presence of light.

They are always on the opposite side of the source of light.

The size and nature of the shadow 15 min depend on the source of light and the position of the object with respect to the source and the screen.

The Umbra is a region of total darkness in the shadow.

The Penumbra is a region of partial darkness in the shadow.

Solar eclipse is formed when the Moon comes between the Earth and the Sun. Lunar eclipse occurs when earth comes in between sun and the moon The triangle formed by the objects and their respective shadows on the ground are similar at a given time and place. This relation can be used to find the height of an object.

TOTAL

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10 min

10 Min 10 Min

15 Min

60 min

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ABL 2.1

Time: 15 min

LEARNING OBJECTIVE: How are shadows formed?

ADVANCE PREPARATION Material List S. No 1 2

3 4 5

Material Torch Torch stand A 4 size cardboard with a hole in the centre Screen Large metal plate Small metal plate

Required Quantity per group 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 what we saw when objects were kept in the path of light? We will go ahead and understand this.

Procedure This can be done as a group activity with 6-10 learners to a group.

2.1a. Place the torch on the torch stand and keep the screen 25 cm away from torch. Place the cardboard such that it is in between the torch and the screen but very close to the torch. The light will pass through the hole in the cardboard and fall on the screen. We will consider this hole as the source of light. Make sure the light from the torch makes a sharp point on the screen.

Place a large metal plate between the source of light and the screen. Observe the screen.

Then take the metal plate away and replace it with the smaller metal. Observe the screen.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you observe on the screen when the large metal plate is kept between the source of light and the screen?

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2. What do you see when the large metal plate is replaced by the smaller plate?

Discussion and Explanation 1. When the big metal piece is kept, there is no light that falls on the screen. It is completely dark. This is because all the rays of light from the source are stopped at the plate and not allowed to fall on the screen.

2. In the second case, the rays of light which hit the plate are not allowed to proceed to the screen but the ones around the plate reach the screen. This results in a dark patch in the middle of the screen and an illuminated part in the rest of the screen.

The dark part is called the shadow.

2.1b.Now, move the smaller plate closer to the screen. Observe the shadow formed on the screen. Then move it away from the screen and again observe the screen.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you observe at the screen when you move the plate towards the screen?

2. What do you observe at the screen when you move the plate towards the torch?

Discussion and Explanation 1. When the plate is moved towards the screen, the shadow becomes smaller.

2. When the plate is moved towards the source of light it becomes bigger. So we can say that the distance between the source of light and the object determined the size of the shadow.

Let us observe a tree. In the morning, the shadow of the tree will be long and towards the west of tree. In the afternoon, with the sun overhead, the shadow is smaller and very close to the tree. In the evening, the shadow is again long, and this time towards the east of the tree.

This can be explained in this way:  In the morning, the sun is further away from the Earth and is rising from the east. So it forms a long shadow towards the west.  In the afternoon, the sun is the closest to the earth and overhead. So the shadow is formed very close to the tree and is smaller.  In the evening, again the sun has gone further away from the earth toward the west. So the shadow is longer and to the east.

KEY MESSAGES  

Shadows are formed by opaque objects in the presence of light.

They are always on the opposite side of the source of light.

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

The size and nature of the shadow depend on the source of light and the position of the object with respect to the source and the screen.

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 Place an object firmly on the table. Take a torch and keep it on the table facing the object at a distance of 25 cm. Switch it on. Slowly lift the torch and take it over the object to the other side, always maintaining the 25 cm distance from the object. Observe the change in the shadow of the object.

INTERESTING INFORMATION   

The sun is very large compared to objects on earth. Thus, when a bird is flying very close to the ground, we see its shadow on the ground. If it is flying at a great height that is away, no shadow is found on the ground.

An aircraft flying at a great height will not cast a shadow for the same reason. But a helicopter or a small plane, which flies closer to the ground, does cast its shadow.

Shadow play or shadow puppetry isan ancient form of storytelling and entertainment which uses flat articulated figures (shadow puppets) to create shadows. Shadow puppets are cut-out figures which are held between a source of light and a translucent screen. The cut-out shapes of the puppets sometimes include translucent colour or other types of detailing. Various effects can be achieved by moving both the puppets and the light source. A talented puppeteer can make the figures appear to walk, dance, fight, nod and laugh.

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ABL 2.2

Time: 10 min

LEARNING OBJECTIVE: What are Umbra and Penumbra?

ADVANCE PREPARATION Material List S. No 1 2 3 4

Material Required Quantity per group Torch 1 per class Torch stand 1 per class An opaque object on a 1 per class stand Screen 1 per class

Things to do Get the figures of the shadows with the umbra and the penumbra clearly marked on a chart paper to show it to the learner. This activity can be demonstrated to the whole class as the explanation will be done to all of them together.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We learnt about how the shadows were formed in the previous activity. Now we will learn different parts of the shadows.

Procedure Fix the torch on the stand and the screen about 30 cm from the torch. The torch gives out light from more than one point. We call this extended source. Place the object between the torch and the screen and see that the shadow of this object falls on the screen. Observe the shadow especially the center of the shadow and the side of the shadow. Move the object away and towards the screen and observe what is seen on the screen.

UNDERSTANDING THE ACTIVITY Leading questions 1. When the object is kept in between the torch and the screen what do you see on the screen?

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2. Is there a difference between the darkness of the shadow in the center and the sides of the image formed on the screen?

3. Does this light and dark areas change when the objects is moved towards and away from the screen?

Discussion and Explanation The shadow seen on the screen will be darker in the center and lighter in the sides. The darker area is called the Umbra, where no light falls. The penumbra is the part, which surrounds the umbra. Some rays of light fall on this region and partially illuminate it. This is shown in the figure below.

Chart 3: Umbra and Penumbra of a shadow

When the object is moved towards the source the Umbra decreases and Penumbra increases. When the object is moved away from the source the Umbra increases and Penumbra decreases. *

KEY MESSAGES:  

The Umbra is a region of total darkness in the shadow.

The Penumbra is a region of partial darkness in the shadow.

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.

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ABL 2.3

Time: 10 min

LEARNING OBJECTIVE: How does a Solar Eclipse occur?

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

Material Globe or Ball Torch Torch stand Pith ball small String

Required Quantity per group 1 per class 1 per class 1 per class 1 per class 1 m per class

Things to do The activity only shows, the way that eclipses are formed, it does not show about the complete and partial eclipses, which instructor has to explain as given in the discussion.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity Remember how shadows are formed when an opaque object comes in between the source of light and the screen.

Procedure Place the torch on a stand and place the globe or the ball at a distance of 30 cm from it. The ball should be stationary. Take the pith ball and tie the string so that it can be suspended. Switch on the light. Now, slowly bring the suspended pith ball between the torch and the ball. Observe what you see on the ball.

Now, try this activity again with the pith ball coming between the torch and the ball but its shadow not falling on the ball. At this time the pith ball, torch and the ball are not in a straight line.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you see when the torch is switched on?

2. What do you see when the pith ball is brought between the torch and the ball?

3. What kind of shadow can you see on the ball?

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Discussion and Explanation 1. When the torch is switched on, the ball is illuminated and looks bright.

2. When the pith ball is brought in between the torch and the ball, its shadow falls on the ball.

3. This shadow has an Umbra region and a Penumbra region.

Now, consider that the torch is the Sun, the ball is the Earth and the pith ball is the Moon. When the pith ball comes in between the torch and ball, it means that the Moon is coming between the Sun and the Earth. The Moon's shadow falls in the Earth. So the people who live in the area where the shadow falls will not see the Sun as the Moon is stopping the rays of the Sun falling on the Earth. This is called a Solar Eclipse. 'To Eclipse' means to hide. Here the Sun is hidden and so it is called the Solar Eclipse.

The people who are in the Umbra region will see a complete eclipse, i.e., the whole Sun will be blocked. Those who live in the Penumbra region will see a partial eclipse i.e., only some part of the Sun will be blocked.

The Moon comes between the Sun and the Earth once every month on the new moon day. But we do not see the solar eclipse every month. This is because there is a tilt of the Moon’s orbit around the Earth and the Earth's orbit around the Sun. So they are not in a straight line. So, as we saw in the second part of the experiment, the shadow of the Moon does not fall on the Earth.

Chart 4: Solar Eclipse

KEY MESSAGES: 

Solar eclipse is formed when the Moon comes between the Earth and the Sun.

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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 There are four types of solar eclipses 1. Total, when the sun is completely obscured by the moon.

2. Annular, when the sun and moon are exactly in line, but apparent size of the moon is smaller than that of the sun.

3. Hybrid, an intermediate between a total and an annular eclipse.

4. Partial, when the sun and moon are not exactly in line, and moon only partially obscures the sun.

One should never look at the sun with naked eyes, and never during the solar eclipse as it can damage our eyes. Special glasses, with filters are available in the market, which should be used to view the eclipse.

Another way of viewing the eclipse is by making an arrangement so that the reflection of the sun falls on the wall. This can be viewed without any harm.

Time: 10 min

ABL 2.4 LEARNING OBJECTIVE: How does a Lunar Eclipse occur?

Note to Instructor: The activity only shows, the way that eclipses are formed; it does not show about the complete and partial eclipses, which instructor has to explain as given in the discussion.

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

Material Globe or Ball Torch Torch stand Pith ball small String

Required Quantity per group 1 per class 1 per class 1 per class 1 per class 1 m per class

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Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Remember how shadows are formed when an opaque object comes in between the source of light and the screen.

Procedure Place the torch on a stand and place the globe or the ball at a distance of 30 cm from it. The ball should be stationary. Take the pith ball and tie the string so that it can be suspended. Switch on the light. Now, slowly take the suspended pith ball around the ball so that the ball comes in between the pith ball and the torch. So you will have the torch, the ball and the pith ball in a line respectively. Observe what you see on the pith ball.

Now, try this activity again with the ball coming between the torch and the pith ball but its shadow not falling on the pith ball. At this time the torch, the ball and pith ball are not in a straight line.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you see when the torch is switched on?

2. What do you see when the pith ball is suspended in such a way that the ball comes between the torch and the pith ball?

3. What kind of shadow can you see on the pith ball?

Discussion and Explanation 1. When the torch is switched on, the ball is illuminated and looks bright.

2. When the pith ball is taken around the ball and when the torch, ball and the pith ball are in a straight line, the shadow of the ball covers the pith ball.

3. Now, consider that the torch is the Sun, the ball is the Earth and the pith ball is the Moon. When the ball comes in between the torch and pith ball, it means that the Earth comes between the Sun and the Moon. The Earth's shadow falls on the Moon. So the people who live in the area facing the Moon will not be able to see it. Here the Earth stops the rays of the Sun falling on the Moon. 'Lunar' is a word associated with the Moon. Here, the Moon is hidden and so it is called the Lunar Eclipse.

The Earth comes between the Sun and the Moon once every month on the full moon day. But we do not see the lunar eclipse every month. This is because there is a tilt of the Moon’s orbit around the Earth and the Agastya International Foundation. For Internal Circulation only.

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Earth's orbit around the Sun. So they are not in a straight line. So, as we saw in the second part of the experiment, the shadow of the Earth does not fall on the Moon.

Chart 5: Stages of Lunar eclipse

KEY MESSAGE: 

Lunar Eclipse occurs when the Earth comes between the Sun and the Moon.

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.

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INTERESTING INFORMATION The shadow of the Earth can be divided into two distinctive parts: the Umbra and Penumbra. Within the umbra, there are no direct rays of the sun. However, as a result of the Sun’s large angular size, solar illumination is only partially blocked in the outer portion of the Earth’s shadow, which is given the name penumbra. A penumbral eclipse occurs when the Moon passes through the Earth’s penumbra. The penumbra causes a subtle darkening of the Moon's surface. A partial lunar eclipse occurs when the Moon passes partially through the Umbra. A total lunar eclipse is seen when the Moon passes completely through the Umbra region of the Earth's shadow. The figure 2.4.1 shows the path of the Moon during a total lunar eclipse.

Time: 15 min

ABL 2.5 LEARNING OBJECTIVE: What are the applications of shadows?

(To find the height of a tree using is shadow.)

ADVANCE PREPARATION Material List S. No. 1 2 3

Material Measuring tape 1 meter long stick Black board/white board / paper to do calculations

Required Quantity per group 1 per class 1 per class 1 per class

Things to do This activity should be done in a place where the shadow of the object whose height you have to measure should fall completely on the ground. An open field or a playground is the best place to do this if there is a tree or a long object present there. Instead of tree, height of buildings, poles, or any tall object can also be determined.

Safety Precautions Not Applicable

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SESSION Link to known information/previous activity Not Applicable Procedure This activity should be done in groups of 6 to 8 learners.

Place the longmetre stick firmly on the ground. The stick will form a shadow. Measure the length of the shadow. Let us assume that it is x cm. Now, measure the length of the shadow of the tree. Let it by y cm. (remember that all the units in the calculations should be same). We know that the height of the stick is 1 m, i.e., 100 cm.

This is how we can calculate the height of the tree.

The triangle formed by the tree and its shadow is similar to the triangle formed by the stick and its shadow.

Thus, by the properties of similar triangles, the ratios of the heights of the objects to its shadows will be similar.

Therefore, Height of the tree length of shadow of tree

=

Height of stick length of shadow of stick

Height of stick = 100 cm.

Length of shadow of stick = x cm.

Length of shadow of tree = y cm.

Substituting these values in the above equation, we get, Height of the tree y cm x cm => Height of tree = 100 * y x

=

100 cm

cm

Leading questions Not Applicable Discussion and Explanation Not Applicable

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KEY MESSAGE: 

The triangle formed by the objects and their respective shadows on the ground are similar at a given time and place. This relation can be used to find the height of an object.

LEARNING CHECK 1. Complete this crossword with clues given below.

1

6

4 2

3

7

5

DOWN 1. You will see non-luminous objects only when this falls of them.

3. The object becomes hot because it _________ heat from the Sun. 4. This material will form complete shadow.

6. This is an eclipse when the Moon is hidden by the shadow.

7. Light is a form of ________.

ACROSS 2. This material allows almost all rays of light to pass through it.

5. This is the darkest part of the shadow.

2. Using a torch as the Sun and two learners as Moon and Earth, show how Lunar and Solar eclipses occur.

3. State if the following statements are true or false. If false, correct them. a. When an opaque object is moved towards the source of light, the shadow of the object decreases. b. When you go to school, your shadow will be seen to your east. c. Every time the moon comes between the Earth and the Sun, a Solar Eclipse takes place. d. Lunar eclipse takes place when the Moon comes between the Sun and the Earth.

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e. The shadow of the tree will be shortest at noon.

4. Find the length of the shadow of the tree if its height is 3 m, the height of the building near it the buildings shadow is 1500 cm long.

WEB RESOURCES 

Use of shadows to tell a story: http://www.indianetzone.com/33/shadow_theatre_indian_form_art.htm



Hand shadowgraphy

 

http://www.youtube.com/watch?v=UAF_CxUvalo http://www.mreclipse.com/Special/SEprimer.html http://wiki.answers.com/Q/What_are_the_different_types_of_eclipse

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is 20 m and

36

ABL 3: REFLECTION OF LIGHT Activity

Learning Objective  

3.1

What are the characteristics of an image formed by a plane mirror?

  

 3.2

What is the distance of the image from the mirror?

Key Message The image formed by the plane mirror is erect.

Image is formed behind the mirror.

Size of the image is the same as the object.

Images formed by the plane mirror are virtual.

The image formed by the plane mirror is always a lateral image of the object.

The distance of object from the mirror is always the same as that of its image from the mirror.

Time

20 Min

10 min



3.3

3ACTIVITIES

What are Laws of Reflection?

Point of Incidence: It is the point where the incident ray strikes the surface of the mirror.  Normal: It is the perpendicular drawn to the surface of mirror at the point of incidence.  Incident Ray: The ray of light falling on the mirror.  Reflected Ray: The ray bounced back from the mirror.  Angle of Incidence: The angle between incident ray and the normal.  Angle of Reflection: The angle between reflected ray and the normal.

TOTAL TIME

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30 min

60 Min

37 Time: 20 min

ABL 3.1

LEARNING OBJECTIVE: What are the characteristics of an image formed by a plane mirror?

ADVANCE PREPARATION Material List S. No. 1 2 3

Material Plane Mirror Candle Screen

Required Quantity per group 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 Not Applicable Procedure This can be done as a group activity with 6 to 10 learners to a group.

3.1.a. Place the mirror firmly on the table. Explain that the mirror is called a plane mirror as it is not curved but is flat. Light the candle and place it in front of the mirror. Ask the learners to observe what they see in the mirror. Now, move the candle towards and away from the mirror. Observe the mirror.

Now, place the screen behind the mirror. Move it towards and away from the mirror to catch the image of the candle flame on it. Then place the screen in front of the mirror. Again move it so that you can catch the image of the flame. Observe the place where the image can be caught on screen.

UNDERSTANDING THE ACTIVITY Leading questions 1. What do you see in the mirror when the candle is lit?

2. What do you observe in the mirror when the candle is moved towards or away from the mirror?

3. Were you able to catch the image of the candle flame when the screen is kept behind the mirror?

4. Can you catch the image of the candle flame when the screen is kept in front of the mirror?

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Discussion and Explanation 1. When the candle is kept before the mirror, it is also seen in the mirror. The candle is the object and what is seen in the mirror is called the image of the candle. The image is of the same size as that of the candle and the image looks the same as the candle. This, we say that the image is erect. (It is not inverted or upside down).

2. When the candle is moved towards the mirror, the image also moves towards the mirror. Similarly, when the candle is moved away from the mirror, the image also moves away from the mirror.

3. When we keep the screen behind the mirror, the image does not fall on it.

4. The image is also not caught on the screen when it is kept in front of the mirror. If the image is not caught on the screen, then it is called a virtual image.

3.1.b. Ask one of the learners to stand in front of the Plane Mirror. Ask her to lift her left hand. Observe which hand the image lifts. Ask her to pull her right ear. Observe which ear the image pulls.

UNDERSTANDING THE ACTIVITY Leading questions 1. Do you see yourself in the mirror?

2. Is the image exactly like you are?

3. Which hand did the image lift when you lifted your left hand?

4. Which ear did the image pull when you pulled your right ear?

Discussion and Explanation You will see an exact replica of yourself in the mirror. But when you lift your left hand, the image will lift its right hand. Similarly, when you pull your right ear, it will pull its left ear. So the image formed in the Plane Mirror is not the exact replica of yourself but an image with is inverted sideways, i.e., your left is its right and your right is its left. This kind of image is called a Lateral Image. So a plane mirror forms a Lateral Image.

3.1.c. Place the white sheet of paper on the table and secure it. Place the mirror on the paper and mark it.

Write the letter 'W' in front of the mirror. Observe the image in the mirror.

Leading questions 1. What do you see in the mirror?

2. How does it look?

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Fig 5: Lateral image formed by a Plane Mirror

Note to Instructor: You must draw the above image on the board while explaining lateral image formation.

Discussion and Explanation The image of the letter 'W' is seen in the mirror. But it looks like M. So this is a lateral inverted image of the object.

KEY MESSAGES     

The image formed by the plane mirror is erect.

Image is formed behind the mirror.

Size of the image is the same as the object.

Images formed by the plane mirror are virtual.

The image formed by the plane mirror is always a lateral image of the object.

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.

VOCABULARY  

Plane Mirror: A mirror that is flat and not curved is called a Plane Mirror.

Erect Image: The image which is in the same direction of the object, i.e., the top and bottom of the object is also the top and bottom of the image, is called an Erect Image.

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   

Inverted Image: If the image formed is upside down as that of the object, i.e., the top of the object is the bottom of the image, then this image is called the Inverted Image.

Real Image: The image that can be caught on the screen is called a Real Image.

Virtual Image: The image that cannot be caught on the screen is called a Virtual Image.

Lateral image: In an image, when the left of the object looks like the right and the right of the image looks like the left, it is called a Lateral Image.

TRY IT YOURSELF 1. Write your name on a paper and look at it in the mirror. How does it look?

2. If you notice an ambulance, the word AMBULANCE is written in the reverse order. Why?

INTERESTING INFORMATION It is good to know the differences between the real and the virtual images. So, if you see an inverted image, you will know that it is real and if the image cannot be captured on screen, it is a virtual image.

S. No. 1 2 3

Real Image It can be captured on the screen The rays of light, after reflection, meet at a point.

It is always inverted (upside down)

Virtual Image It cannot be captured on the screen The rays of light, after reflection, seem to meet at a point.

It is always erect but laterally inverted (Inverted sideways, i.e., left become right and right becomes left)

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41 Time: 10 min

ABL 3.2

LEARNING OBJECTIVE: What is the distance of the image from the mirror?

ADVANCE PREPARATION Material List S. No. 1 2 3

Material Chess board Plane mirror Eraser

Required Quantity per group 1 1 1

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Recollect from the previous activity, that when the object moves, so does the image.

Procedure This can be done as a group activity with 6 to 10 learners to a group.

Place the chessboard on the table. Place the plane mirror exactly in the middle of the board. Now, place eraser or any object, two squares away from the mirror. Note the position of image inside the mirror in terms of squares from the mirror. Shift the object to the 4th square from the mirror and note down the position inside the mirror. Similarly, shift the object to different positions on the chessboard and at every move note the position of the image.

UNDERSTANDING THE ACTIVITY Leading questions 1. Can you see the object in the mirror?

2. When object is placed two squares from the mirror, how far is the image from the mirror?

3. When object is moved four squares away from the mirror, how far is the image?

4. What happens to the image whenever the place of the object is changed?

Discussion and Explanation 1. We see the image of the object in the mirror.

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2. When the object is two squares away from the mirror, the image is also two squared from the mirror.

3. When the object is 4 squares away so is the image.

4. Similarly, whenever the object is moved, the image also moves and the distance of the object from the mirror is always the same as that of its image from the mirror.

KEY MESSAGES 

The distance of object from the mirror is always the same as that of its image from the mirror.

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.

Time: 30 min

ABL 3.3 LEARNING OBJECTIVE: What are Laws of Reflection?

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

Material White sheet Plane mirror Paper pins (all pins) Sharp pointed Pencil Ruler Protector

Required Quantity per group 1 per class 1 per class 10 per class 1 per class 1 per class 1 per class

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SESSION Link to known information/previous activity Not Applicable Procedure Note to Instructor - Instructor should do this activity before demonstrating this in class. The instructor should demonstrate the activity to the learners first and then allow them to conduct this experiment. Do help them to do it properly.

This can be done as a group activity with 6 to 10 learners to a group.

Place the paper on the table and secure it with the help of pins. Place the mirror on one side of the paper, about 3 cm from the shorter side. Mark the mirror with a pencil. Let us call it line AB. Draw a line perpendicular to the mirror using a protector. Let us call it CD, with point D on line AB. Draw another line inside the angle BDC and name it line DE. Place two pins on the line DE and name them P 1 and P2.

Now look at the mirror from the angle ADC at the level of the table. Can you see the images of the pins P 1 and P2? Now, move your head in such a way the P 1 and P2 are in a straight line, i.e., they are one behind the other.

Now take one more pin and place it so that image of P1 and P2 and the pin in your hand are in a straight line.

Name this point P3. Now place the fourth pin in such a way that the images of P 1 and P2 and P3 and the pin in your hand are all in a straight line. Name this point P 4.

Mark the points P3 and P4. Draw a line joining points P3, P4 and D. Name this line DF. Remove the mirror and the pins and look at the diagrams formed. What do you observe?

Measure the angles EDC and CDF.

UNDERSTANDING THE ACTIVITY Leading questions 1. Can you see the two pins in the mirror?

2. Can you move your head in such a way that you can see both the pins in a straight line?

3. Are the three pins in a straight line?

4. How do you know that they are in a straight line?

5. Are the four pins in a straight line?

Discussion and Explanation The figure 6 that you will see on the paper will look like the one shown below.

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Fig 6: Diagram showing the reflection of light from a Plane Mirror

Here we saw that the rays of light hit the mirror and were thrown back. This is called reflection of light. When we looked at the images of pins 1 and 2, one behind the other, we actually traced one of the rays of light. By placing the pins 3 and 4 we traced the ray of light, which was reflected from pins 1 and 2.

Look at the diagram on the paper. Line AB is the mirror. The objects (pins 1 and 2) and their images are seen on the same side of the mirror. Line DC is perpendicular to the line AB. This is known as the 'Normal'. The line ED, which contains points P1 and P2 is called the Incident Ray. I.e., the ray that goes from the object to the mirror. The line DF that contains points P3 and P4 is called the Reflected Ray, as this is the ray that is reflected after the incident ray hits the mirror.

The point at which the incident ray hits the mirror is called the Point of Incidence (point D).

Angle EDC, i.e., the angle formed by the incident ray and the normal is called the Angle of Incidence (i). Angle CDF, i.e., the angle formed by the normal and the reflected ray, is called the Angle of Reflection (r).

You will notice that the angle of incidence is equal to the angle of reflection.

As we have drawn the incident ray, reflected ray and the normal on the paper, we can say that they all are in the same plane.

The reflected ray obeys certain laws. They are called Laws of Reflection.

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Laws of Reflection 1. The angle of reflection is equal to the angle of incidence.

2. The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.

KEY MESSAGES      

Point of Incidence: It is the point where the incident ray strikes the surface of the mirror.

Normal: It is the perpendicular drawn to the surface of mirror at the point of incidence.

Incident Ray: The ray of light falling on the mirror.

Reflected Ray: The ray bounced back from the mirror.

Angle of Incidence: The angle between incident ray and the normal.

Angle of Reflection: The angle between reflected ray and the normal.

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.

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ABL 4: REGULAR AND IRREGULAR REFLECTION Activity

Learning Objective 

4.1

4.2

2ACTIVITIES

Do all surfaces make similar reflections?

What is the distance of the image and object from the mirror in a plane mirror? (using ray diagram)

 



Key Message Smooth surfaces form clear images.

Rough surfaces form distorted images.

Laws of reflection are followed in both the cases.

In a plane mirror, the distance between the object and mirror, image and mirror is always the same.

TOTAL TIME

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Time

15 min

25 min

40 Min

47

Time: 15 min

ABL 4.1

LEARNING OBJECTIVE- Do all surfaces make similar reflections?

ADVANCE PREPARATION Material List S. No. 1 2

Material Aluminum foil (A 4 Size) Tub of water

Required Quantity per group 1 sheet per class 1 per class

Things to do Keep the tub of water ready before the class so that it becomes still. Be careful not to disturb it.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have learnt how reflection of light takes place from the surface of the mirror. Now let us see how it takes place from other surfaces.

Procedure Group the learners around the tub of water. The water is still. The learners can see their faces reflected from the water. Now, tap the tub. Observe what happens to the reflection.

Take the aluminum foil. Take care that the foil is smooth. Face the shiny side towards the learners. Ask them to note what they see in the foil. Now crumple the foil and then smoothen it with your hand. Now ask the learners to observe what they see in the foil.

UNDERSTANDING THE ACTIVITY Leading questions 1. What did you see in the still water?

2. What happened to the reflection after the tub was tapped?

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3. What did you see when the aluminum foil was smooth?

4. What did you see after the foil had been crumpled?

Discussion and Explanation 1. In the still water, clear image of the faces and other objects is seen.

2. When the tub is tapped, ripples are caused in the water and the clear reflection disappears and distorted image is seen.

3. Similarly, in the case of the aluminum foil, the smooth surface reflects clear image.

4. After it is crumpled, the image is distorted.

Now, when the incident rays fall on a smooth surface, all of them are reflected back in the same direction, so a clear image of the object is seen. This can be seen in the figure- 7 shown below.

Figure 7: Reflection of rays from rough and smooth surfaces

Now, when the incident rays hit the rough or uneven surface, it is reflected back in different directions. This is why we see a distorted image. This is also shown in the figure above.

In both the cases, the laws of reflection are observed, but the difference in surface causes the images to be different. We have already learnt that the angle of incidence and angle of reflection are same according to laws of reflection. The normal at every point of incidence in a smooth surface are parallel to each other, thus making all the reflected rays parallel to each other. This is different in a rough surface. The normal at every point of the surface where the incident rays hit are not parallel to each other. So, even with the angle of incidence and angle of reflection being the same, the reflected rays are not parallel to each other. This causes the distorted image. This is shown in the figure- 8 below.

Fig 8: Reflection form uneven surface

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KEY MESSAGES   

Smooth surfaces form clear images.

Rough surfaces form distorted images.

Laws of reflection are followed in both the cases.

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.

Time: 25 min

ABL 4.2

LEARNING OBJECTIVE: What is the Distance of the image and object from the mirror in a plane mirror? (using ray diagram) Note to Instructor - This is an activity, which will have to be done by the instructor first and then allow the learners to do it on their own. Each one of them can do it individually in their notebooks. A ray diagram should be drawn on a chart paper and put up after the demonstration by the instructor is over.

ADVANCE PREPARATION Material List

Things to do Not Applicable

S. No. 1 2 3 4

Material White sheet of paper per class Pencil per class Ruler per class Protector per class

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Safety Precautions Not Applicable SESSION Link to known information/previous activity Recollect the laws of reflection.

Procedure Place the paper on the table and secure it. Draw a line l, which represents the mirror. Mark a point O, which will represent the object. We know that the rays of light from the object will fall on the mirror and reflect back. Draw 4 incident rays from point O to the mirror as shown in the figure. Let these rays hit the mirror (represented by line l) in points A, B, C and D. Draw reflected rays from these four points. For this, there will have to be a normal drawn at every point. Now, keeping the angle of reflection same as that of the angle of incidence draw the reflected rays.

The diagram will look like the one shown in fig9.

Fig 9: Diagram showing the incident and reflected rays

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Now, extend all the reflected rays to the other side of the mirror.

UNDERSTANDING THE ACTIVITY Leading questions 1. What happens to the extended reflected rays?

2. What do you expect to see at the point where they meet?

Discussion and Explanation You will see that all the extended lines meet at a point on the other side of the mirror. Actually they appear to meet, as the image formed is virtual. Name the point at which the rays meet as X. If you measure perpendicular distance of the point O to the mirror and the distance of point X to the mirror it will be the same. This is because, in a plane mirror, the distance between the object and the image from the mirror will always be the same.

The diagram will look as in fig 10.

Fig 10: Reflected rays seem to meet at a point beyond the mirror

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KEY MESSAGES In a plane mirror, the distance between the object and mirror, image and mirror is always the same.

LEARNING CHECK 1. Find out the letters of English alphabet in which the image if formed in a plane mirror appears exactly like the letter itself.

2. Raju is observing his image in a plane mirror. The distance between the mirror and image is 4m. What will be the distance between Raju and the mirror if he moves 1m towards the mirror?

3. What happens when light is incident on plane mirror at Normal?

4. If a ray of light makes an angle of 320 with the normal, then what is the measure of the angle of the reflected ray and the normal?

5. If the angle between the incident ray and the reflected ray is 60 0, what is the angle of reflection?

6. List out the characteristics of the image formed by a plane mirror.

7. When you stand in front of a highly polished stone, you see an image. What kind of image is this?

8. We know that light travels in a straight line. How can we change its path?

9. You are standing 1 m and 50 cm away from a plane mirror. How far is your image from you?

10. Is the image formed by a plane mirror real or virtual?

WEB RESOURCES   

http://www.arvindguptatoys.com/arvindgupta/mirror.pdf http://www.stressfreestudies.com/science/class-7-science/physics-7/2011/10/physics-7-reflection-oflight-part-1/ http://www.phys.hawaii.edu/~varner/PHYS272_Spr10/Lectures/PDF_archive/lecture_38.pdf

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ABL 5: REFLECTION OF LIGHT FROM SPHERICAL MIRRORS Activity

Learning Objective

Key Message 

5.1

5.2

5.3

5.4

Are there any mirrors other than plane mirrors?

What are the types of spherical mirrors?

What are the parts of a spherical mirror?



There exist different types of mirrors. Plane mirrors and spherical mirrors are two of the many types of mirrors.

The images formed by curved surfaces differ from those formed by plane mirrors.  A convex mirror is a curved mirror in which the bulged surface is the reflecting surface.  A concave mirror is a curved mirror in which the bulged surface is coated and the opposing surface is the reflecting surface.  The center of the sphere, which is equidistant from any point on the surface of the mirror, is known as the Center of Curvature.  The center of the mirror is called the Pole of the mirror.  The distance from the Pole to the Centre of Curvature is known as the Radius of Curvature,  The imaginary line that passes through the Pole and Centre of Curvature of a spherical mirror is called the Principal Axis of the mirror.  The Focusis exactly midway between the Centre of Curvature and the Pole.  The distance from the Pole to the Focus is known as the Focal Length of the mirror

How do we locate the pole, center of curvature, focus, focal length, radius of curvature and principal axis for a concave mirror of radius of

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Time

10 Min

10 Min

15 Min

15 Min

54

curvature 20cm?

Four rules to locate the image formed by spherical mirrors are as follows. 

5.5

5

What are the rules to locate the images formed by spherical mirrors?

Rule 1: Any ray incident parallel to the principle axis is reflected back by the spherical surface and passes through the focus F.  Rule 2: Any ray incident along the focus F after reflection from the spherical surface becomes parallel to the principle axis.  Rule 3: Any ray incident along the centre of curvature C retraces its path after reflection from the mirror because it is incident normally on the spherical surface.  Rule 4: Any ray which strikes the mirror at its pole P is reflected such that its angle of incidence with respect to the principal axis is equal to its angle of reflection.

TOTAL

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15 Min

65 Min

Time: 10 min

ABL 5.1

55

LEARNING OBJECTIVE: Are there any mirrors other than plane mirrors?

ADVANCE PREPARATION Material List S. No. 1 2

Material Plane mirror New stainless steel spoon

Required Quantity per group 1 per class 1 per class

Things to do Find the right kind of spoons for the activity. The spoons used should have no scratches. Use spoons that are round.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity Recollect how the plane mirror formed images.

Procedure Ask a learner to look into a mirror and tell the class what he sees in the mirror. Now, give him the spoon and ask him to keep the outside of the spoon in front of his face. Ask him what he sees. Gradually increase the distance of the spoon and face.

Next, ask him to look at his face using the inner side of the spoon. Again move the spoon further away from the face. Ask him what he observed.

UNDERSTANDING THE ACTIVITY Leading questions 1. What did you see when you looked into the mirror?

2. What did you see when you held the outside of the spoon in front of your face?

3. What happened when the distance between your face and the spoon was decreased?

4. What did you see when you held the inside of the spoon in front of your face? When the spoon was moved away from your face, did you see?

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Discussion and Explanation 1. You will see that the plane mirror reflects your face as it is, except that it is a lateral inverted image.

2. The image of your face formed on the outside of the spoon is just like the one you see in the plane mirror but enlarged.

3. When we move the spoon closer, the image becomes bigger.

4. When you look at the inside of the spoon, the image formed is inverted. Here too, when we move the spoon closer, the image becomes bigger and when it is moved farther away, the image becomes smaller.

A mirror is any surface that is smooth and reflects light without diffusing it. The spoon acts as a mirror but the image seen is different than that of the plane mirror. As the surface of the spoon in curved, it is called a spherical mirror.

KEY MESSAGES 1. There exist different types of mirrors. Plane mirrors and spherical mirrors are two of the many types of mirrors.

2. The images formed by curved surfaces differ from those formed by plane mirrors.

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.

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ABL 5.2 LEARNING OBJECTIVE: What are the types of spherical mirrors?

ADVANCE PREPARATION Material List S. No. 1 2 3

Material Rubber Ball Aluminum foil/Silver paper Knife

Required Quantity per group 1 per class 1 per class 1 per class

Things to do Not Applicable Safety Precautions The knife can be dangerous. Be careful while using it and teach the learners how to take care while using the knife.

SESSION Link to known information/previous activity We learnt that there were different types of mirrors and also saw that the spoon acts like a mirror. Now we will see what type of mirror the spoon is.

Procedure Show the rubber ball to the learners. Ask them the shape of the ball. Now, very neatly, cut the ball into half with the help of the knife. Hold up the two halves to show them to the learners.

Now, wrap the inner surface of one half with aluminum foil/silver paper and cover the outer surface of the other half with the foil/silver paper.

UNDERSTANDING THE ACTIVITY Leading questions 1. What is the shape of the ball?

2. How do the surfaces covered by the aluminum foil/silver paper look like?

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Discussion and Explanation 1. The shape of the ball is called a sphere. When we cut the ball in half, you can see two curved surfaces, one on the outside of the ball and the other in the inside of the ball.

2. The half of the ball that is covered with aluminum foil/silver paper on the outside will act as a mirror on the outside surface. This type of mirror is called the convex mirror.

The half of the ball that is covered with aluminum foil/silver paper on the inside will act as a mirror on the inside surface. This is called a concave mirror.

These kinds of mirrors are called spherical mirrors (because they are part of the sphere).

Chart 6: Formation of spherical mirrors

KEY MESSAGES  

A convex mirror is a curved mirror in which the bulged surface is the reflecting surface.

A concave mirror is a curved mirror in which the bulged surface is coated and the opposing surface is the reflecting surface.

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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.

Time: 15 min

ABL 5.3

LEARNING OBJECTIVE: What are the parts of a spherical mirror?

ADVANCE PREPARATION Material List S. No. 1 2 3

Material Models prepared in the previous activity - concave and convex mirrors Teacher's compass (the one used for drawing on the board) Teacher's Scale

Required Quantity 1 per class 1 per class 1 per class

Things to do This is a session where many important concepts and definitions will be explained. It will be useful if these diagrams and definitions are written on chart papers and kept ready. Whenever one concept is explained, that chart can be shown. These charts can be displayed in class till the concept is understood well.

Safety Precautions Not Applicable

SESSION Link to known information/previous activity We learnt about the two types of spherical mirrors and how they are formed. Now learn more about them.

Procedure Show the learners the two halves of the ball, which have been covered by aluminum foil - one on the inside and one on the outside. Explain to them that the center of the ball plays an important part of the image Agastya International Foundation. For Internal Circulation only.

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formed by the mirrors. As every part of the mirror is explained, draw it one the black board. Then put up the charts made.

UNDERSTANDING THE ACTIVITY Leading questions 1. How do you draw a circle on a paper?

2. Do you know what a radius is?

3. Do you know what a radius of a sphere means?

Discussion and Explanation 1. When you draw a circle on a paper, you use a compass.

2. Radius is the distance from the centre of a circle to any point on its circumference.

3. The distance between the pointed end of the compass and the point of the pencil is the radius of the circle. The distance between any points of the circle is the same from the place of the pointed end of the compass. This point is called the center of the circle. Similarly, the center of a sphere is a point, inside the sphere, which is equidistant from any point of the sphere.

We have seen how the sphere was cut into half and there were two types of mirrors created - the concave mirror and the convex mirror. The center of the sphere plays an important part of the image formed by the mirrors. This is the point that is equidistant from any point on the surface of the mirror. This is known as the Center of Curvature. In the Chart 7, this point is denoted by 'C'.

Chart 7: Parts of the spherical mirror

The center of the mirror is called the Pole of the mirror. To be specific, it is called the geometric pole of the mirror. In Chart 7, this point is denoted by 'P' Agastya International Foundation. For Internal Circulation only.

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The distance from the Pole to the Centre of Curvature is known as the Radius of Curvature, i.e., the distance CP is the radius of curvature. This is equal to the radius of the sphere or the ball from which the mirror has been made. (Represented by R) The imaginary line that passes through the Pole and Centre of Curvature of a spherical mirror is called the Principal Axis of the mirror.

In the Chart 8, allow a beam of light parallel to the principle axis incident on the concave mirror. After reflection all the rays converge at a point on the principle axis. This is called the principle focus (F) and its distance from the pole measured along the principle axis is called the focal length (f). The focal length is related to the curvature of the mirror. đ?‘…

For all spherical mirrors, focal length, đ?‘“ = where R is the radius of curvature.

2

Chart 8: Reflection of parallel beam of rays in a concave mirror

In the case of the convex mirror, the incident beam parallel to the principle axis is rendered divergent after reflection. The reflected rays appear to diverge from a point on the principle axis. This is called the principle đ?‘…

focus (F) and its distance from the pole is the focal length (f) i.e., focal length, đ?‘“ = where R is the radius of 2

curvature.

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Chart 9: Reflection of parallel beam of rays in a convex mirror

KEY MESSAGES      

The center of the sphere, which is equidistant from any point on the surface of the mirror, is known as the Center of Curvature.

The center of the mirror is called the Pole of the mirror.

The distance from the Pole to the Centre of Curvature is known as the Radius of Curvature, The imaginary line that passes through the Pole and Centre of Curvature of a spherical mirror is called the Principal Axis of the mirror.

The Focusis exactly midway between the Centre of Curvature and the Pole.

The distance from the Pole to the Focus is known as the Focal Length of the mirror.

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.

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Time: 15 min

63

ABL 5.4 LEARNING OBJECTIVE: How do we locate the pole, center of curvature, focus, focal length, radius of curvature and principal axis for a concave mirror of radius of curvature 20 cm?

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

Material Teacher's compass (the one used for drawing on the board) Teacher's Scale Geometrical compass Scale Pencils

Required Quantity per learner 1 per class 1 per class 1 per learner 1 per learner 2 per learner - one for the compass and the other to draw

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity Recollect all the parts of the mirror we learnt in the previous activity.

Procedure Note to Instructor - As the teacher shows how to draw the diagram on the board, the learners should follow him/her. They have to draw in their notebooks. After every step, go around and see if the learners are doing it properly. It is very important that each learner learns this, as it is the basis of the diagrams that they will have to draw later.

Draw a straight line. Take the compass and measure a length of 20 cm with help of ruler. Place the sharp end of the compass on a point on the straight line and draw an arc that cuts the straight line.

Mark the point where the arc touches the straight line as 'P' as this is the Pole of the mirror.

Mark the point where the sharp tip of the compass was kept as 'C'. This is the Centre of Curvature of the Mirror.

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Produce the line PC and mark it as a Principal Axis.

Mark the midpoint between P and C. It is focal point F.

UNDERSTANDING THE ACTIVITY Leading questions 1. Measure the distance between C and any point of the mirror (the arc).

2. Measure the distance between F and P. Discussion and Explanation 1. Once you draw the diagram, you will understand what we learnt in the previous activity better. The distance of any point from C is always the same. In this case it will be 20 cm as the radius of Curvature is 20 cm.

2. The distance between F and P is 10 cm. This is half the radius of curvature, as we learnt previously.

Chart 10: Parts of a concave mirror

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KEY MESSAGES: Not Applicable

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 Try drawing the diagrams for various other measures of radius of curvature.

Time: 15 min

ABL 5.5

LEARNING OBJECTIVE: What are the rules to locate the images formed by spherical mirrors?

Note to Instructor - The learners should be able to draw the diagram showing the mirror, center of curvature, Focus and Principal axis. These diagrams are important and so each learner must learn how to draw them.

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

Material Scale Geometrical compass Scale Pencils

Required Quantity per learner 1 per class 1 per learner 1 per learner 2 per learner - one for the compass and the other to draw.

Things to do Not Applicable Safety Precautions Not Applicable

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SESSION Link to known information/previous activity We have already learnt about the parts of the mirror. Now we will learn how the rays of light that fall on the mirror behave.

Procedure Nature of the object:  If the incident rays diverge from the object, the object is said to be real.  If the incident rays appear to converge from an object then the object is virtual.

Nature of the Image:  If the reflected rays converge at a point then the image formed is real.  If the reflected rays appear to diverge from a point then the image formed is virtual.

Draw the concave mirror and the Principal Axis on the board. With inputs from the learners, mark the Centre of Curvature, the Focus, and the Pole.

Explain to the learners that there is a need to trace the path of at least two rays before and after reflection from the mirror. The point where the two reflected rays meet is the position of the real image. The point from where the reflected rays appear to diverge is the position of virtual image.

In the Chart 11, AB is an object on the principle axis. To know the position of the image formed by the concave mirror, choose two rays starting from the object (A).  Ray 1 incident parallel to the principle axis passes through F after reflection.  Ray 2 incident along the centre of curvature (AC) retraces its path after reflection from the mirror because it is incident normally on the spherical surface.  The light starting from B passing along the principle axis is reflected along the same line. Hence, we can see an image formed when we drop a perpendicular at B l on the priciple axis.

The two reflected rays meet at A| which is the image of A. Draw A|B|perpendicular to the principle axis. A |B|is the real image of AB.

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Chart 11: Position of the image in a concave mirror when the object is beyond C In the Chart 12, AB is an object on the principle axis. To know the position of the image formed by the convex mirror, choose two rays starting from the object (A).  Ray 1 incident parallel to the principle axis is reflected back by the spherical surface and appears to pass through F.  Ray 2 incident along the centre of curvature (AC) is reflected back.  The light starting from B passing along the principle axis is reflected along the same line. Hence, we can see an image formed when we drop a perpendicular at B l on the priciple axis.

The two reflected rays meet at A| which is the image of A. Draw A|B|perpendicular to the principle axis. A |B|is the virtual image of AB.

Chart 12: Formation of the image in a convex mirror Agastya International Foundation. For Internal Circulation only.

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Leading questions Not Applicable

Discussion and Explanation Not Applicable

KEY MESSAGES: Four rules to locate the image formed by spherical mirrors are as follows.    

Rule 1: Any ray incident parallel to the principle axis is reflected back by the spherical surface and passes through the focus F. Rule 2: Any ray incident along the focus F after reflection from the spherical surface becomes parallel to the principle axis.

Rule 3: Any ray incident along the centre of curvature C retraces its path after reflection from the mirror because it is incident normally on the spherical surface.

Rule 4: Any ray which strikes the mirror at its pole P is reflected such that its angle of incidence with respect to the principal axis is equal to its angle of reflection.

Note to Instructor: To find the position of the image, trace the paths of at least two incident rays and find their points of intersection or divergence after reflection from the spherical mirror.

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.

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ABL 6: IMAGE FORMATION IN CONCAVE MIRRORS Activity

Learning Objective

Key Message

Time

In a concave mirror: 



6.1

What is the nature of the image formed by a concave mirror?

  

6.2 2

When the object is placed beyond C, the image is formed between F and C. This image is real, inverted, and smaller than the object.

When the object is placed at C, the image is formed at C. The image is real, inverted, and is the same size of the object.

When the object is placed between F and C, 30 Min the image is formed beyond C. The image is real, inverted and larger than the object.

When the object is placed at F, an image is not formed.

When the object is placed between F and the mirror, the image is virtual, formed on the other side of the mirror, erect and larger than the object.

How do we draw ray diagrams for images formed by concave mirror?

25 min TOTAL

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55 Min

70

Time: 30 min

ABL 6.1 LEARNING OBJECTIVE: What is the nature of the image formed by a concave mirror?

Note to Instructor: Make sure that learners know about parts of a concave mirror before you begin. If they do not, please take 10 minutes to give them an introduction from ABL 5.3.

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

Material Mirror stand Concave mirror Screen Candle White chart paper Pencil Scale

Required Quantity per group 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 The mirror, screen and the candle should be handled with care.

SESSION Link to known information/previous activity We know that the light reflects from the spherical mirrors. Now we will see how and where the images are formed.

Procedure This activity will have to be demonstrated by the instructor first and then the learners can be allowed to do it on his or her own in groups of 6 to 10. The instructor should insist that the learners take down the readings.

This will help them to understand the concept better.

Secure the white chart paper neatly on the table. Draw a straight line in the middle of the paper, lengthwise.

This line will be the Principal Axis of the mirror. Fix the mirror firmly on the stand and place it on the line Agastya International Foundation. For Internal Circulation only.

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drawn. Mark the position of the mirror on the paper. Mark the Focus (F) on the Principal Axis (the focal length will be given on the mirror). This can be done by measuring the focal length from the mirror towards the front of the mirror. Now, mark the Center of Curvature (C) of the mirror. Remember, the radius of curvature is twice that of the focal length.

The candle acts as the object. Light the candle and place it in different places, on the Principal Axis to see the kind of images formed. Note all this information in the table given below. Get the learners to make this table in their notebooks before the start of the activity.

Figure 11 – Reference table – position of Image and object S. No. Position of Object Position of Image Image seen

1. Place the object beyond C i.e., at a distance more than the radius of curvature from the mirror. Mark this point. Move the screen, on the same side of the mirror as the object, along the Principal Axis till the image is seen on it. Then adjust the screen so that the image is the sharpest. Mark the position of the image.

Observe the kind of image seen.

2. Now, place the object at point C. Again observe the place where the image is formed and the type of image formed.

3. Next, keep the object between C and F. Observe the image.

4. Then, keep the object at F and observe the image.

5. Finally, keep the object between the mirror and F and observe the image.

UNDERSTANDING THE ACTIVITY Leading questions 1. Where is the image seen when the object kept beyond C? What kind of image is this?

2. Where is the image seen when the object kept at C? What kind of image is this?

3. Where is the image seen when the object kept between C and F? What kind of image is this?

4. Where is the image seen when the object kept at F? What kind of image is this?

5. Where is the image seen when the object kept between the mirror and F? What kind of image is this?

Discussion and Explanation Let us take each of these positions of the object one at a time.

1. When the object is placed beyond C, the image is formed between F and C. The image is captured on the screen. So this is a real image. (Only real images can be captured on screen). This image is inverted, and smaller than the object.

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2. When the object is placed at C, the image is formed at C. The image is a real image. The image is inverted, and is the same size of the object.

3. When the object is placed between F and C, the image is formed beyond C. The image is real, inverted and larger than the object.

4. When the object is placed at F, an image is not formed.

5. When the object is placed between F and the mirror, the image cannot be caught on screen. So it is a virtual image. The image is seen to be formed on the other side of the mirror. This image is erect and larger than the object.

This information can be tabulated as under: S. No. Position of Object Position of Image 1 Beyond C Between F and C 2 At C At C 3 Between F and C Beyond C 4 At F No image formed 5 Between F and the On the other side of mirror the mirror

Type of Image seen Real, inverted, smaller Real, inverted, same size Real, inverted, larger Virtual, erect, larger

KEY MESSAGES: In a concave mirror:     

When the object is placed beyond C, the image is formed between F and C. This image is real, inverted, and smaller than the object.

When the object is placed at C, the image is formed at C. The image is real, inverted, and is the same size of the object.

When the object is placed between F and C, the image is formed beyond C. The image is real, inverted and larger than the object.

When the object is placed at F, an image is not formed.

When the object is placed between F and the mirror, the image is virtual, formed on the other side of the mirror, erect and larger than the object.

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.

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ABL 6.2

LEARNING OBJECTIVE: How do we draw ray diagrams for images formed by concave mirror?

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

Material Scale Geometrical compass Scale Pencils

Required Quantity per learner 1 1 per learner 1 per learner 2 per learner - one for the compass and the other to draw.

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity In the last activity we saw how and where the images are formed. Now we will learn to draw the ray diagram.

To find the position of the image, trace the paths of at least two incident rays and find their points of intersection or divergence after reflection from the spherical mirror(Refer Activity 4.5).

Procedure The diagrams have to be drawn by each learner in their notebooks. Initially, for the first couple of diagrams, the instructor will have to go around the classroom to check if the learners have done it correctly. Once they get the expertise of making the basic diagrams, it will be easier for them. Insist that they practice the diagrams a few times on their own at home.

Draw the concave mirror and the Principal Axis on the board. With inputs from the learners, mark the Centre of Curvature, the Focus, and the Pole. Now take the positions of the object one at a time.

1. Draw the object (in the shape of an arrow facing upwards) beyond C. Using the first rule, draw a line, parallel to the Principal axis from the top of the object to the mirror. This ray, when reflected will pass through the Focus. So draw the reflected ray from the point where the incident ray touches the mirror through the Focus. Remember to draw the arrows denoting the path of the incident and the reflected ray.

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Now, using the second rule, draw the incident ray from the top of the object through the Focus to the mirror. The reflected ray will be parallel to the Principal Axis. Draw the reflected ray.

The point at which the two reflected rays meet is the point where the image will be formed. The point of intersection is the top of the image. Draw the image with the arrow marking the top of the image.

You will see that the image is formed between F and C; it is inverted and smaller than the object.

Chart 13:Formation of the image when object is beyond C

2. In the second case, draw the object at C. Using the two rules draw the incident rays and the reflected ray.

The point of intersection is the place where the image is formed. The image is formed at C. The image is inverted, and is the same size of the object.

Chart 14: Formation of the image when object is at C

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3. Next, draw the object between C and F. Using the two rules; draw the incident rays and the reflected ray. The image is formed beyond C. The image is inverted, and larger than the object.

Chart 15: Formation of the image when object is between F and C

4. Then, keep the object at F. Here, there will be another rule is used. This rule states that the ray of light from the object, if it goes through the center of curvature, will be reflected back through the center of curvature. So first draw a parallel incident ray to the mirror and its reflected ray through the Focus. The second incident ray will start from the top of the image, pass through C and hit the mirror. This ray will be reflected along the same path it came. Here, we will notice that the two reflected rays do not intersect but are parallel to each other. So they do not form an image.

Chart 16: Formation of the image when object is at F

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5. In the last of the ray diagrams, draw an object between F and the mirror. Use the first two rules, and draw the incident and reflected rays. You will notice that the reflected rays do not intersect but are divergent, i.e., they go away from each other. Now extend these rays on the other end. These rays will meet at a point on the other side of the mirror. The image will be formed there. This image is erect, larger and because we cannot catch it on the screen, it is a virtual image.

Chart 17: Formation of the image when object is between F and P of the mirror

Leading Questions Not Applicable Discussion and Explanation Not Applicable

KEY MESSAGES Not Applicable

LEARNING CHECK 1. If the radius of curvature of a concave mirror is x, what is the focal length of that mirror?

2. An image formed by a spherical mirror is erect, what kind of image is it?

3. An object is kept at a distance of 50 cm from the concave mirror of focal length 20 cm. What kind of image will it form?

4. If the object and the image are of the same size, where is the object kept in front of the concave mirror?

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5.

6.

7.

8.

In a concave mirror, when will you get an enlarged virtual image of the object?

What kind of mirror are the inside and the outside of the polished spoon?

For which position of an object does a concave mirror produce an inverted, magnified and real image?

Use a ray diagram to show the formation of a real image by a concave mirror.

WEB RESOURCE   

http://www.physicsclassroom.com/class/refln/u13l3d.cfm http://www.tutorvista.com/content/science/science-ii/reflection-light/formation-concave-mirror.php http://www.physicsclassroom.com/mmedia/optics/rdcmc.cfm

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