Welcome dear students! Today we are going to learn about Light from Class 8 Science. The world is largely known through the senses. The sense of sight is one of the most important senses. Through it we see mountains, rivers, trees, plants, chairs, people and so many other things around us. We also see clouds, rainbows and birds flying in the sky. At night we see the moon and the stars. You are able to see the words and sentences printed on this page. How is seeing made possible? Let us explore this together.
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Section thirteen point one asks what makes things visible. Have you ever thought how we see various objects? You may say that eyes see the objects. But, can you see an object in the dark? It means that eyes alone cannot see any object. It is only when light from an object enters our eyes that we see the object. The light may have been emitted by the object, or may have been reflected by it. You learnt in Class seven that a polished or a shiny surface can act as a mirror. A mirror changes the direction of light that falls on it. Can you tell in which direction the light falling on a surface will be reflected? Let us find out.
Now let us move to section thirteen point two, the Laws of Reflection. We begin with Activity thirteen point one. Fix a white sheet of paper on a drawing board or a table. Take a comb and close all its openings except one in the middle. You can use a strip of black paper for this purpose. Hold the comb perpendicular to the sheet of paper. Throw light from a torch through the opening of the comb from one side. In Figure thirteen point one, we see the arrangement for showing reflection. With slight adjustment of the torch and the comb you will see a ray of light along the paper on the other side of the comb. Keep the comb and the torch steady. Place a strip of plane mirror in the path of the light ray. What do you observe? After striking the mirror, the ray of light is reflected in another direction. The light ray, which strikes any surface, is called the incident ray. The ray that comes back from the surface after reflection is known as the reflected ray. A ray of light is an idealisation. In reality, we have a narrow beam of light which is made up of several rays. For simplicity, we use the term ray for a narrow beam of light.
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Draw lines showing the position of the plane mirror, the incident ray and the reflected ray on the paper with the help of your friends. Remove the mirror and the comb. Draw a line making an angle of ninety degrees to the line representing the mirror at the point where the incident ray strikes the mirror. This line is known as the normal to the reflecting surface at that point, as shown in Figure thirteen point two. The angle between the normal and incident ray is called the angle of incidence, written as angle i. The angle between the normal and the reflected ray is known as the angle of reflection, written as angle r, as shown in Figure thirteen point three. Measure the angle of incidence and the angle of reflection. Repeat the activity several times by changing the angle of incidence. Enter the data in Table thirteen point one. Do you see any relation between the angle of incidence and the angle of reflection? Are they approximately equal? If the experiment is carried out carefully, it is seen that the angle of incidence is always equal to the angle of reflection. This is one of the laws of reflection.
Let us perform another activity on reflection. What would happen if I threw the light on the mirror along the normal? Activity thirteen point two asks you to perform Activity thirteen point one again. This time use a sheet of stiff paper or a chart paper. Let the sheet project a little beyond the edge of the table, as shown in Figure thirteen point four. Cut the projecting portion of the sheet in the middle. Look at the reflected ray. Make sure that the reflected ray extends to the projected portion of the paper. Bend that part of the projected portion on which the reflected ray falls. Can you still see the reflected ray? Bring the paper back to the original position. Can you see the reflected ray again? What do you infer? When the whole sheet of paper is spread on the table, it represents one plane. The incident ray, the normal at the point of incidence and the reflected ray are all in this plane. When you bend the paper you create a plane different from the plane in which the incident ray and the normal lie. Then you do not see the reflected ray. What does it indicate? It indicates that the incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. This is another law of reflection.
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Paheli and Boojho performed these activities outside the classroom with the Sun as the source of light instead of a torch. You, too, can use the Sun as the source of light. These activities can also be performed by making use of the Ray Streak Apparatus available in the kit prepared by NCERT. Boojho remembered that in Class seven, he had studied some features of the image of an object formed by a plane mirror. Paheli asked him to recall those features: Was the image erect or upside down? Was it of the same size as the object? Did the image appear at the same distance behind the mirror as the object was in front of it? Could it be obtained on a screen? Let us understand a little more about the formation of an image by a plane mirror in the following way.
Activity thirteen point three describes a source of light O placed in front of a plane mirror PQ. Two rays OA and OC are incident on it, as shown in Figure thirteen point five. Can you find out the direction of the reflected rays? Draw normals to the surface of the mirror PQ, at the points A and C. Then draw the reflected rays at the points A and C. How would you draw these rays? Call the reflected rays AB and CD, respectively. Extend them further. Do they meet? Extend them backwards. Do they meet now? If they meet, mark this point as I. For a viewer’s eye at E, do the reflected rays appear to come from the point I? Since the reflected rays do not actually meet at I, but only appear to do so, we say that a virtual image of the point O is formed at I. As you have learnt already in Class seven, such an image cannot be obtained on a screen. You may recall that in an image formed by a mirror the left of the object appears on the right and the right appears on the left. This is known as lateral inversion.
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Now let us move to section thirteen point three, Regular and Diffused Reflection. Activity thirteen point four asks you to imagine that parallel rays are incident on an irregular surface as shown in Figure thirteen point six. Remember that the laws of reflection are valid at each point of the surface. Use these laws to construct reflected rays at various points. Are they parallel to one another? You will find that these rays are reflected in different directions, as shown in Figure thirteen point seven. When all the parallel rays reflected from a rough or irregular surface are not parallel, the reflection is known as diffused or irregular reflection. Remember that the diffused reflection is not due to the failure of the laws of reflection. It is caused by the irregularities in the reflecting surface, like that of a cardboard. On the other hand, reflection from a smooth surface like that of a mirror is called regular reflection, as shown in Figure thirteen point eight. Images are formed by regular reflection.
Do we see all objects due to reflected light? Nearly everything you see around is seen due to reflected light. Moon, for example, receives light from the Sun and reflects it. That is how we see the moon. The objects which shine in the light of other objects are called illuminated objects. Can you name some other such objects? There are other objects, which give their own light, such as the Sun, fire, flame of a candle and an electric lamp. Their light falls on our eyes. That is how we see them. The objects which emit their own light are known as luminous objects.
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Let us consider section thirteen point four, Reflected Light Can be Reflected Again. Recall the last time you visited a hair dresser. She or he makes you sit in front of a mirror. After your hair cut is complete, she or he holds a mirror behind you to show you how the hair has been cut, as shown in Figure thirteen point nine. Do you know how you could see the hair at the back of your head? Paheli recalls having constructed a periscope as an Extended Activity in Class six. The periscope makes use of two plane mirrors. Can you explain how reflection from the two mirrors enables you to see objects which are not visible directly? Periscopes are used in submarines, tanks and also by soldiers in bunkers to see things outside.
Next is section thirteen point five, Multiple Images. You are aware that a plane mirror forms only a single image of an object. What happens if two plane mirrors are used in combination? Let us see. Activity thirteen point five instructs you to take two plane mirrors. Set them at right angles to each other with their edges touching, as shown in Figure thirteen point ten. To hinge them you can use adhesive tape. Place a coin in between the mirrors. How many images of the coin do you see? Now hinge the mirrors using the adhesive tape at different angles, say forty five degrees, sixty degrees, one hundred twenty degrees, one hundred eighty degrees and so on. Place some object, say a candle, in between them. Note down the number of images of the object in each case. Finally, set the two mirrors parallel to each other. Find out how many images of a candle placed between them are formed, as shown in Figure thirteen point eleven. Can you now explain how you can see the back of your head at the hair dresser’s shop? This idea of number of images formed by mirrors placed at an angle to one another is used in a kaleidoscope to make numerous beautiful patterns. You can also make a kaleidoscope yourself.
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Kaleidoscope Activity thirteen point six explains how to make one. To make a kaleidoscope, get three rectangular mirror strips each about fifteen centimetres long and four centimetres wide. Join them together to form a prism as shown in Figure thirteen point twelve part a. Fix this arrangement of mirrors in a circular cardboard tube or tube of a thick chart paper. Make sure that the tube is slightly longer than the mirror strips. Close one end of the tube by a cardboard disc having a hole in the centre, through which you can see, as shown in Figure thirteen point twelve part b. To make the disc durable, paste a piece of transparent plastic sheet under the cardboard disc. At the other end, touching the mirrors, fix a circular plane glass plate, as shown in Figure thirteen point twelve part c. Place on this glass plate several small pieces of coloured glass, which are broken pieces of coloured bangles. Close this end of the tube by a ground glass plate. Allow enough space for the colour pieces to move around. Your kaleidoscope is ready. When you peek through the hole, you will be able to see a variety of patterns in the tube. An interesting feature of a kaleidoscope is that you will never see the same pattern again. Designers of wallpapers and fabrics and artists often use kaleidoscopes to get ideas for new patterns. To make your toy attractive, you can wrap the kaleidoscope in a coloured paper.
Activity thirteen point seven involves getting a plane mirror of a suitable size. Place it in a bowl, also called a katori, as shown in Figure thirteen point thirteen. Fill the bowl with water. Put this arrangement near a window in such a way that direct sunlight falls on the mirror. Adjust the position of the bowl so that the reflected light from the mirror falls on a wall. If the wall is not white, fix a sheet of white paper on it. Reflected light will be seen to have many colours. How can you explain this? The mirror and water form a prism. As you learnt in Class seven, this breaks up the light into its colours. Splitting of light into its colours is known as dispersion of light. Rainbow is a natural phenomenon showing dispersion.
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Now we come to section thirteen point six, Sunlight, White or Coloured. In Class seven, you learnt that the sunlight is referred to as white light. You also learnt that it consists of seven colours. Here is another activity, Activity thirteen point seven, showing that sunlight consists of several colours.
Section thirteen point seven asks, What is inside Our Eyes? We see things only when light coming from them enters our eyes. Eye is one of our most important sense organs. It is, therefore, important to understand its structure and working. The eye has a roughly spherical shape. The outer coat of the eye is white. It is tough so that it can protect the interior of the eye from accidents. Its transparent front part is called cornea, as shown in Figure thirteen point fourteen. Behind the cornea, we find a dark muscular structure called iris. In the iris, there is a small opening called the pupil. The size of the pupil is controlled by the iris. The iris is that part of eye which gives it its distinctive colour. When we say that a person has green eyes, we refer actually to the colour of the iris. The iris controls the amount of light entering into the eye. Let us see how.
Caution: For this activity, never use a laser torch. Activity thirteen point eight instructs you to look into your friend’s eye. Observe the size of the pupil. Throw light on her eye with a torch. Observe the pupil now. Switch off the torch, and observe her pupil once again. Do you notice any change in the size of the pupil? In which case was the pupil larger? Why do you think it was so? In which case do you need to allow more light in the eye, when the light is dim or bright? Behind the pupil of the eye is a lens which is thicker in the centre. What kind of lens is thicker at the centre? Recall what you learnt about lenses in Class seven. The lens focuses light on the back of the eye, on a layer called retina, as shown in Figure thirteen point fourteen. The retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve. There are two kinds of cells. First, cones, which are sensitive to bright light. Second, rods, which are sensitive to dim light. Cones sense colour. At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot. Its existence can be demonstrated as follows.
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Activity thirteen point nine asks you to make a round mark and a cross on a sheet of paper with the spot to the right of the cross, as shown in Figure thirteen point fifteen. The distance between two marks may be six to eight centimetres. Hold the sheet of paper at an arm’s length from the eye. Close your left eye. Look continuously at the cross. Move the sheet slowly towards you, keeping your eye on the cross. What do you find? Does the round mark disappear at some point? Now close your right eye. Look at the round mark now and repeat the activity. Does the cross disappear? The disappearance of the cross or the round mark shows that there is a point on the retina which cannot send messages to the brain when light falls on it.
The impression of an image does not vanish immediately from the retina. It persists there for about one sixteenth of a second. So, if still images of a moving object are flashed on the eye at a rate faster than sixteen per second, then the eye perceives this object as moving. Activity thirteen point ten instructs you to get a square piece of cardboard of size six to eight centimetres. Make two holes as shown in Figure thirteen point sixteen. Thread a string through the two holes. Draw or paste a cage on one side of the cardboard and a bird on the other side. Twist the string and make the card twirl rapidly. Do you see the bird in the cage? The movies that we see are actually a number of separate pictures in proper sequence. They are made to move across the eye usually at the rate of twenty four pictures per second, which is faster than sixteen per second. So, we see a moving picture.
Nature has provided eyes with eyelids to prevent any object from entering the eye. Eyelids also shut out light when not required. Eye is such a wonderful instrument that it can clearly see distant objects as well as objects nearby. The minimum distance at which the eye can see objects distinctly varies with age. The most comfortable distance at which one can read with a normal eye is about twenty five centimetres. Some persons can see objects close to them clearly but cannot see distant objects so clearly. On the other hand, some persons cannot see objects nearby clearly but they can see distant objects quite well. With suitable corrective lenses, these defects of the eye can be corrected. Sometimes, particularly in old age, eyesight becomes foggy. It is due to the eye lens becoming cloudy. When it happens, persons are said to have cataract. There is a loss of vision, sometimes extremely severe. It is possible to treat this defect. The opaque lens is removed and a new artificial lens is inserted. Modern technology has made this procedure simpler and safer.
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Section thirteen point eight covers Care of the Eyes. It is necessary that you take proper care of your eyes. If there is any problem you should go to an eye specialist. Have a regular checkup. If advised, use suitable spectacles. Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too much light, like that of the Sun, a powerful lamp or a laser torch can injure the retina. Do not look at the Sun or a powerful light directly. Never rub your eyes. If particles of dust go into your eyes, wash your eyes with clean water. If there is no improvement go to a doctor. Always read at the normal distance for vision. Do not read by bringing the book too close to your eyes or keeping it too far. You learnt about balanced diet in Class six. If food is deficient in some components, eyes may also suffer. Lack of vitamin A in foodstuff is responsible for many eye troubles. Most common amongst them is night blindness. One should, therefore, include in the diet components which have vitamin A. Raw carrots, broccoli and green vegetables such as spinach and cod liver oil are rich in vitamin A. Eggs, milk, curd, cheese, butter and fruits such as papaya and mango are also rich in vitamin A.
Section thirteen point nine discusses Visually Impaired Persons Can Read and Write. Some persons, including children, can be visually impaired. They have very limited vision to see things. Some persons cannot see at all since birth. Some persons may lose their eyesight because of a disease or an injury. Such persons try to identify things by touching and listening to voices more carefully. They develop their other senses more sharply. However, additional resources can enable them to develop their capabilities further. Non-optical and optical aids for visually impaired persons include visual aids, tactile aids using the sense of touch, auditory aids using the sense of hearing and electronic aids. Visual aids can magnify words, can provide suitable intensity of light and material at proper distances. Tactual aids, including Braille writer slate and stylus, help the visually challenged persons in taking notes, reading and writing. Auditory aids include cassettes, tape recorders, talking books and other such devices. Electronic aids, such as talking calculators and computers, are also available for performing many computational tasks. Closed circuit television, also an electronic aid, enlarges printed material with suitable contrast and illumination. Nowadays, use of audio CDs and voice boxes with computers are also very helpful for listening to and writing the desired text. Optical aids include bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids. While the lens combinations are used to rectify visual limitations, telescopic aids are available to view chalkboard and class demonstrations.
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Section thirteen point ten explains What is the Braille System? The most popular resource for visually challenged persons is Braille. Louis Braille, himself a visually challenged person, developed a system for visually challenged persons and published it in eighteen twenty one. The present system was adopted in nineteen thirty two. There is Braille code for common languages, mathematics and scientific notation. Many Indian languages can be read using the Braille system. Braille system has sixty three dot patterns or characters. Each character represents a letter, a combination of letters, a common word or a grammatical sign. Dots are arranged in cells of two vertical rows of three dots each. Patterns of dots to represent some English letters and some common words are shown in Figure thirteen point eighteen. For example, the letter C is represented by a top left dot and a middle left dot. The letter A is a top left dot. The letter T is a top left dot, a middle left dot, and a bottom left dot. These patterns when embossed on Braille sheets help visually challenged persons to recognise words by touching. To make them easier to touch, the dots are raised slightly. Visually impaired people learn the Braille system by beginning with letters, then special characters and letter combinations. Methods depend upon recognition by touching. Each character has to be memorised. Braille texts can be produced by hand or by machine. Typewriter like devices and printing machines have now been developed. Some visually impaired Indians have great achievements to their credit. Diwakar, a child prodigy has given amazing performances as a singer. Ravindra Jain, born completely visually impaired, obtained his Sangeet Prabhakar degree from Allahabad. He had shown his excellence as a lyricist, singer and music composer. Lal Advani, himself visually impaired, established an Association for special education and rehabilitation of disabled in India. Besides this, he represented India on Braille problems in UNESCO. Helen A. Keller, an American author and lecturer, is perhaps the most well known and inspiring visually challenged person. She lost her sight when she was only eighteen months old. But because of her resolve and courage she could complete her graduation from a university. She wrote a number of books including The Story of my Life published in nineteen zero three.
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Now let us carefully go through the exercises. Exercise one: Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain. Answer: In a dark room, we cannot see objects in the room because there is no light to be reflected from them into our eyes. We can see objects outside the room only if light from those objects enters our eyes through a window or opening.
Exercise two: Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection? Answer: Regular reflection occurs when parallel rays of light strike a smooth, polished surface and reflect parallel to each other. Diffused or irregular reflection occurs when parallel rays strike a rough or irregular surface and reflect in different directions. Diffused reflection does not mean the failure of the laws of reflection. It is caused by the irregularities in the reflecting surface, and the laws of reflection are valid at each point of the surface.
Exercise three: Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case. Answer: a) Polished wooden table will show regular reflection because its surface is smooth and polished. b) Chalk powder will show diffused reflection because its surface is rough and irregular. c) Cardboard surface will show diffused reflection because its surface is rough. d) Marble floor with water spread over it will show regular reflection because the water creates a smooth surface. e) Mirror will show regular reflection because its surface is highly polished and smooth. f) Piece of paper will show diffused reflection because its surface is rough and uneven.
Exercise four: State the laws of reflection. Answer: The two laws of reflection are: First, the angle of incidence is always equal to the angle of reflection. Second, the incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
Exercise five: Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane. Answer: Perform Activity thirteen point two. Use a sheet of stiff paper projecting beyond a table. Cut the projecting portion in the middle. Shine light so the reflected ray falls on the projected portion. When you bend that part of the paper, the reflected ray disappears from view. When you bring the paper back to the original flat position, the reflected ray is visible again. This shows that the incident ray, the normal, and the reflected ray all lie in the same plane.
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Exercise six: Fill in the blanks in the following. Answer: a) A person one metre in front of a plane mirror seems to be two metres away from his image. b) If you touch your left ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with left hand. c) The size of the pupil becomes large when you see in dim light. d) Night birds have fewer cones than rods in their eyes.
Exercise seven: Angle of incidence is equal to the angle of reflection. Choose the correct option. Answer: a) Always.
Exercise eight: Image formed by a plane mirror is. Choose the correct option. Answer: b) virtual, behind the mirror and of the same size as the object.
Exercise nine: Describe the construction of a kaleidoscope. Answer: To make a kaleidoscope, join three rectangular mirror strips, each about fifteen centimetres long and four centimetres wide, to form a prism. Fix this arrangement in a circular cardboard tube slightly longer than the mirrors. Close one end with a cardboard disc having a central viewing hole, reinforced with transparent plastic. At the other end, fix a circular plane glass plate touching the mirrors. Place small pieces of coloured glass on this plate. Close this end with a ground glass plate, leaving space for the pieces to move.
Exercise ten: Draw a labelled sketch of the human eye. Answer: The sketch should show a roughly spherical shape with the following parts clearly labelled: Cornea as the transparent front part, Iris as the dark muscular structure behind it, Pupil as the small opening in the iris, Lens behind the pupil, Retina as the light sensitive layer at the back, and Optic Nerve connecting the retina to the brain.
Exercise eleven: Gurmit wanted to perform Activity thirteen point eight using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise? Answer: The teacher advised against using a laser torch because laser light is highly intense and concentrated. Looking directly at a laser beam or its reflection can severely injure the retina and cause permanent damage to the eyes.
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Exercise twelve: Explain how you can take care of your eyes. Answer: To care for your eyes, visit an eye specialist regularly and use spectacles if advised. Avoid too little or too much light. Do not look directly at the Sun or powerful lights. Never rub your eyes. Wash eyes with clean water if dust enters. Read at a normal distance of about twenty five centimetres. Include vitamin A rich foods like carrots, spinach, eggs, milk, papaya and mango in your diet.
Exercise thirteen: What is the angle of incidence of a ray if the reflected ray is at an angle of ninety degrees to the incident ray? Answer: The angle of incidence equals the angle of reflection. If the total angle between the incident and reflected ray is ninety degrees, then each angle is half of that. Therefore, the angle of incidence is forty five degrees.
Exercise fourteen: How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by forty centimetres? Answer: When two plane mirrors are parallel to each other, they form an infinite number of images due to multiple reflections.
Exercise fifteen: Two mirrors meet at right angles. A ray of light is incident on one at an angle of thirty degrees as shown in Figure thirteen point nineteen. Draw the reflected ray from the second mirror. Answer: The first mirror reflects the ray at an angle of thirty degrees to the normal. This reflected ray strikes the second mirror. Since the mirrors are at ninety degrees, the geometry ensures that the angle of incidence on the second mirror will be sixty degrees. The ray will reflect from the second mirror at sixty degrees, emerging parallel to the original incident ray but in the opposite direction.
Exercise sixteen: Boojho stands at A just on the side of a plane mirror as shown in Figure thirteen point twenty. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R? Answer: Boojho cannot see his own image because he is standing at the extreme edge of the mirror, outside the field of reflection. He can see the image of object P and Q because light from them can reflect into his eyes, but he cannot see the image of R as it lies outside the mirror's reflective range for his position.
Exercise seventeen: a) Find out the position of the image of an object situated at A in the plane mirror. b) Can Paheli at B see this image? c) Can Boojho at C see this image? d) When Paheli moves from B to C, where does the image of A move? Answer: a) The image of object A will be formed behind the mirror at the same distance as A is in front of it. b) Yes, Paheli at B can see the image. c) Yes, Boojho at C can also see the image. d) The image of A does not move. It remains fixed at the same position behind the mirror regardless of where the observer moves.
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Now let us look at the Extended Learning Activities and Projects. Activity one: Make your own mirror. Take a glass strip or glass slab. Clean it and put it on a white sheet of paper. See yourself in the glass. Next put the glass slab on a black sheet of paper. Again look into the glass. In which case do you see yourself better and why? Answer: You will see yourself better on the black sheet of paper because the black background absorbs most of the light passing through the glass, reducing background glare and allowing the weak reflection from the front surface of the glass to be more visible.
Activity two: Make friends with some visually impaired students. Enquire from them how they read and write. Also find out how they are able to recognise objects, hurdles and currency notes. Answer: This activity encourages direct interaction. Visually impaired students typically use Braille for reading and writing, tactile markers for objects, and distinct textures or sizes for currency notes. They also rely heavily on auditory cues and trained mobility skills.
Activity three: Meet an eye specialist. Get your eye sight checked and discuss how to take care of your eyes. Answer: This is a practical assignment to visit a doctor, undergo vision testing, and receive personalized advice on eye hygiene, diet, and screen time management.
Activity four: Survey your neighbourhood. Find out how many children below the age of twelve years use spectacles. Find out from their parents what, in their view, could be the reason for the weak eyesight of their children. Answer: This survey activity helps students collect real world data. Common reasons reported by parents usually include excessive screen time, poor lighting while reading, genetic factors, and lack of outdoor play.
Finally, let us review the Did You Know section on eye donation. Eyes can be donated by any person as an invaluable gift to visually impaired persons suffering from corneal blindness. The person may be a male or female, of any age, of any social status, using spectacles, or suffering from any normal disease but not AIDS, Hepatitis B or C, rabies, leukemia, lymphoma, tetanus, cholera, or encephalitis. The eyes have to be donated within four to six hours after death at any place, home or hospital. A person who wants to donate the eyes may pledge eyes during his or her lifetime to any registered eye bank. He or she should also inform his or her relatives about this pledge so that they can take necessary action after his or her death. You can also donate a Braille kit.
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To summarize what you have learnt: Light is reflected from all surfaces. Regular reflection takes place when light is incident on smooth, polished and regular surfaces. Diffused or irregular reflection takes place from rough surfaces. Two laws of reflection are that the angle of incidence is equal to the angle of reflection, and the incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface lie in the same plane. Image formed in a plane mirror undergoes lateral inversion. Two mirrors inclined to each other give multiple images. Beautiful patterns are formed in a kaleidoscope because of multiple reflections. Sunlight, called white light, consists of seven colours. Splitting of light into its constituent colours is known as dispersion. Parts of the eye are cornea, iris, pupil, lens, retina and optic nerve. A normal eye can see nearby and distant objects clearly. Visually impaired persons can read and write using the Braille system. Visually impaired persons develop their other senses more sharply to improve their interaction with their environment.
Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]