Science 4

How to learn from this moduleHere is a simple guide for you in going about the module.1. Read and follow the instructions very carefully.2. Take the pretest (20-item multiple-choice test) to determine how much you know about the lessons in the module.3. Check your answers against the correct answers provided at the last page of the module.4. Be very honest in taking the test so you know how much knowledge you already have about the topic.5. Perform all the activities, as these will help you have a better understanding of the topic.6. Take the self-tests at the end of each lesson to determine how much you learned about the lesson.7. Take the posttest (20-item multiple choice test) to assess how much you learned in this module. Have fun in learning these lessons about light. Good luck! What to do before (Pretest)Multiple Choice: Write the letter of the best answer:1. Which of the following is Sir Isaac Newton’s theory that explains light as a particle?a. Corpuscular Theory c. Quantum Theoryb. Electromagnetic Wave Theory d. Wave Theory2. When light hits a smooth surface, it is c. reflected a. bent around corners d. refracted b. polarized3. A ray of light is reflected from a plane mirror. The angle of incidence is 20o. The anglebetween the incident and the reflected ray isa. 10o c. 30ob. 20o d. 40o 2

4. What kind of mirror is used in automobile and trucks to give the driver a wider area andsmaller image of the traffic behind him/her?a. concave mirror c. plane mirrorb. convex mirror d. none of these5. The image in a plane mirror is always c. inverted and reversed. a. erect but reversed. d. inverted but not reversed. b. erect but not reversed.6. When rays parallel to the principal axis of a concave mirror are reflected, they pass through a. any point on the axis.. b. the principal focus. c. the center of curvature of the mirror. d. the point halfway between the focus and the mirror.7. A stick partly submerged obliquely in water appears to be bent at a point where it enters the water surface. Which one of the following gives explanation for this observation? a. Dispersion of light on entering water b. Light does not travel in straight line in water. c. Diffraction of light by the surface of the water d. Refraction of light due to differences in speed of light in air8. The principle involved in the formation of images on lenses isa. aberration. c. reflection.b. dispersion. d. refraction.9. A diamond is a brilliant gem because c. most of the light is refracted. a. it has low index of refraction. d. most of the light is reflected internally. b. it has big critical angle.10. When light travels from air to glass its speeda. increases . c. remains the same.b. decreases. d. increases then decreases.11. The property of light responsible for the formation of colors isa. amplitude . c. velocity.b. quality. d. wavelength.12. Which of the following statements is NOT true about the dispersion of sunlight by a prism? a. The color most bent is red. b. White light consists of waves of varying length. c. Different wavelengths travel with different speed. d. Different wavelengths correspond to different colors. 3

13. After a rainstorm, a rainbow may appear in the sky. Which statement explains this observation? a. Raindrops act as prisms separating sunlight into colors. b. The white clouds are actually prisms composed of different colors. c. The colors of the rainbow come from raindrops in the atmosphere. d. When the sunlight is reflected by the ground towards the clouds, it separates into different colors.14. A piece of coal appears black when viewed in sunlight because it __________ all thelight that falls on it.a. absorbs c. reflectsb. disperses d. transmits15. A red rose appears red because of its ability to a. absorb the red color and reflect all others. b. reflect the red color and absorb all others. c. transmit all colors except red. d. transmit the red color and reflect all others.16. Diffraction of light means that a. light is a transverse wave. b. light is reflected from a film. c. light bends as it enters a different medium. d. light bends as it passes through a small opening.17. The sun appears to be more reddish at sunset than at noon. Which of the followingphenomena is responsible for this effect?a. dispersion c. reflectionb. interference d. scattering18. Which property of light produces bright and dark bands on a screen after light from asource passes through two very narrow slits that are near each other?a. dispersion c. polarizationb. interference d. refraction19. When sunlight falls on soap bubble, the band of colors seen is due toa. dispersion. c. pigments of soap.b. interference. d. refraction.20. Polarization of light is an evidence that light a. is a transverse wave. b. is a longitudinal wave. c. has a particle property. d. wave can destructively interfere with each other. Key to answers on page 30 4

Lesson 1 The Nature of Light What is light? Is it matter or is it energy? Is it a particle or is it a wave? Do you knowthat for centuries, scientists disagreed about the nature of light? Sir Isaac Newton in hiscorpuscular theory of light thought that light is made up of particles that travels throughspace on a straight line. On the other hand, Christian Huygens, a Dutch physicist, thoughtthat light is made up of waves similar to that of water waves. This is called the wave theoryof light. When scientist discovered the interference of light they thought they had proved thatlight consists of waves. They felt that particles did not act this way. Yet, at that time,scientists believed that waves must travel through a medium. They could not explain howwaves of sunlight traveled to the earth through a vacuum or space. Later, it was found thatan electromagnetic wave, such as light, could travel through a vacuum. Electromagneticwaves are disturbances caused by both electric and magnetic fields. According to JamesClerk Maxwell, light is that small part of the electromagnetic spectrum which affects ourvision. Light is propagated in space as electromagnetic waves. This is known aselectromagnetic wave theory of light. More recently, scientists found evidence to prove that light does consist of particles.In photoelectric effect, Einstein discovered that light shining on certain metals can makeelectron jumps out of the metal. Brighter light can make more electrons jump, but they jumpout at the same speed. However, different colors of light make electrons jump out atdifferent speeds. Scientists could explain these observations if light was made up ofparticles of energy called photons. Based on this, the Quantum Theory was proposed byMax Planck in 1900 and advanced by Albert Einstein in 1905. This theory assumes thatlight is radiated in discrete packets or bundles of energy called photons, which also exhibitwave characteristics. Based on the scientists’ investigations of the different behaviors oflight, it is now considered to have dual characteristics – those of a wave and those of aparticle. These behaviors can only be observed under different conditions. Know This When does light behave as a particle? When does it behave as a wave? In general, if light interacts with light such as in interference, it manifests wave behavior. If light interacts with matter like in the photoelectric effect, the particle behavior is strongly manifested. Light of higher frequencies shows more of a particle behavior while light of lower frequencies shows more of the wavelike behavior. 5

What you will doSelf-Test 1.1Direction: Match the theories about the nature of light in column A with their correspondingproponents in column B. Column A Column B Theory Proponent1. Wave Theory a. James Clerk Maxwell2. Corpuscular Theory b. Christian Huygens3. Electromagnetic Theory c. Max Planck4. Quantum Theory d. Sir Isaac Newton Key to answers on page 30Lesson 2 Reflection and Mirrors What can you see when you look at a mirror, or a polished metal or a still pool ofwater? You can see your image. Why? These objects are image reflecting objects.Types of Image There are two types of images formed by reflecting surfaces. They are real andvirtual images. Real image is always inverted and is formed by actual rays of light. It canbe projected on the screen. Virtual image is always erect and is formed by apparent rays oflight. It cannot be projected on the screen.Reflection of Light normal ray When light hits a smooth surface like amirror, light is reflected. Reflection is the incident ir reflectedturning back of light when it hits a barrier. The ray rayangle between the incident ray and the normalrays is called the angle of incidence. The smooth surfaceangle between the reflected ray and the normalray is the angle of reflection. i = angle of incidence r = angle of reflectionThe laws of reflection state that:1. the incident ray, the reflected ray, and the normal to the reflecting surface all lie in the same plane.2. the angle of incidence is equal to the angle of reflection. 6

What you will do Activity 2.1 Image in a Plane Mirror1. Stand in front of a plane mirror. Is your image exactly the same in size as you are? Where is it apparently found?2. Raise your left hand. What hand does your image raise?3. Is your image erect or inverted? Is it real or virtual? The mirrors that we use as looking glasses are plane mirrors. The image formed bya plane mirror is always erect, virtual, laterally reversed, same size as the object and foundto be apparently behind the mirror.Spherical Mirrors There are two kinds of spherical mirrors, theconcave and convex mirrors. If the reflecting surface iscurved inward, it is a concave mirror. If the reflectingsurface is curved outward it is a convex mirror. a. concave mirror b. convex mirrorThere are mirrors terminology which you should know. They are the following:1. Vertex (V) is the middle portion of the mirror. S A V2. Center of curvature (C) is the center of the sphere P r of which the curved mirror is a part. C Ff3. Radius of curvature (r) is the distance of the center of curvature from the vertex.4. Principal axis (P) is the line drawn passing through the vertex and the center of curvature.5. Secondary axis (S) is a line drawn through the center of curvature to any part in the mirror.6. Aperture (A) is the opening of the mirror.7. Focus (F) is the point where the reflected rays meet.8. Focal length (f) is the distance between the focus and the vertex.Remember ThisFor spherical mirrors with small opening, the focal length isone-half the radius of curvature. 7

What you will do Activity 2.2 Image in spherical mirrors1. Get a spoon. This can serve as your mirror.2. Look at the concave surface of the spoon. Place the mirror very near your face. Describe your image.3. Bring the spoon an arm length distance away from you. Describe your image.4. Look now at the convex surface of the spoon. Observe your image as you bring the spoon farther from you. Describe your image.You observed that the position and size of the image changes when the distance of aconcave mirror from the observer varies. For a convex mirror, you observed only onekind of image which is smaller, erect and virtual.Ray Method of Image FormationHow can we construct, locate and describe the image formed by spherical mirrors? To construct the image formed by spherical mirrors by the ray method draw at leasttwo of the following rays from point A on the object (See Figure 2.1): Ray 1 is an incident ray parallel to the A ray 1 principal axis and is reflected through the principal focus. P object ray 2 ray 3 Ray 2 is a ray traveling along a secondary CF V axis and passes through the center of curvature which is reflected back along image itself. Ray 3 is a ray that passes through the Fig. 2.1 focus and is reflected parallel to the Ray method of locating images principal axis.Figure 2.2 summarizes the kind of image formed in a concave mirror at different position ofthe object. Study how the image is constructed using the ray method. Note the kind ofimage formed. 8

Fig. 2.2 Image in a Concave Mirrora. Object is at infinite distance b. Object is located beyond the center of curvature A ray 1 ray 2 object P F CF V image The image is a point at the principal The image is smaller, inverted, real and focus. located between the center of curvaturec. Object is at the center of and the focus. curvature d. Object is between the center of curvature & the principal focus ray 1 ray 2A ray 1object ray 3 P AP F image object image C CFThe image is of the same size, inverted, The image is larger, inverted, real and real and located at the center of located beyond the center of curvature. curvature.e. Object at principal focus f. Object is between principal focus and the mirror ray 2 ray 2 A ray 1 A ray 1 P F object image C objectP CFThe image is at infinity – no image is The image is larger, erect, virtual and observed. located behind the mirror. 9

Image in a convex mirror A C object image F In a convex mirror, the image is alwayssmaller than the object, erect and located behindthe mirror. As the object is brought closer to themirror, the size of the image increases, but it cannever become as large as the object itself. Fig. 2.3 Image in a convex mirrorWhere are mirrors used? Concave mirrors are used in amusement parks to form fantastic images. The convexside view mirror used by automobile and trucks gives a wide field of view and vision. Canyou name other uses of mirrors?The Mirror Equation: Mathematically, the object distance (do), image distance (di) 1= 1 + 1and the focal length (f) of the mirror can be found using the mirror f do diformula: The size of the object (So) and size of image (Si) are Si = didetermined using the size formula: So do The mirror formula is applicable for both concave and convex mirror. The followingconventions are helpful in using the equation for solving problems. Mirror f do diconcavereal image +++virtual image ++ -convex (virtual image) - + - 10

What you will do Self-Test 2.1Direction: Identify the term herein defined, described or referred to in the following:____________ 1. The kind of image that is formed by actual ray of light and can be projected on the screen____________ 2. The angle between the incident ray and the normal ray____________ 3. The kind of mirror that will always produce a smaller, virtual and erect image____________ 4. The distance between the focus and the vertex of a mirror____________ 5. The kind of mirror that will produce an image of the same size as the object, erect and virtual____________ 6. Position of the object in front of a concave mirror that will produce an image that is smaller, inverted and real____________ 7. Position of the object where no image is formed____________ 8. The middle portion of the mirror____________ 9. Spherical mirror used in automobile that gives wider view of area____________ 10. Kind of mirror that will give a virtual, erect and larger image Key to answers on page 30 11

Lesson 3. Refraction and Lenses How does light travel? What happens to the ray of light when it passes throughdifferent media, say air to water? What you will do Activity 3.1 Refraction of light 1. Get a glass half-filled with water. 2. Place a pencil in this glass of water 3. Look at the pencil at the top of the glass. What happens to the pencil? 4. Look from the side of the glass. Do you notice any difference? 5. Remove the pencil out of the water. Is there a difference between the way it looks in water and the way it looks in air? The pencil appears bent when it is partly submerged in water. This shows that a lightray bends as it passes from air to water. The change in direction or the bending of lightwhen it passes from one medium to another of different optical density is called refraction.Refraction also makes the water appear shallower. Because of refraction, a fish appearshigher in the water when viewed from the bank than it actually is. A teaspoon placed in aglass of water appears to be bent or broken at the surface of the water. A coin placed in thebottom of a teacup, out of the line of vision of an observer, will become visible when the cupis filled with waterRefraction and the Speed of Light When light travels from air to water, its speed decreases. A medium is opticallydense if it slows down the speed of light. Water is optically denser than air. When light travels from an optically less dense to denser medium at an angle, sayfrom air to glass, light bends toward the normal (Figure 3.1a). When light travels from adenser to a less dense medium at an angle, say from glass to air, the light bends away fromthe normal (Figure 3.1b). The angle formed between the incident ray and the normal iscalled the angle of incidence, i, and the angle between the refracted and the normal iscalled the angle of refraction, r. 12

incident normal incident normal i = angle ofray ray ray incidence rayair i glass i r = angle of refractionglass refracted air r ray r refracted (a) (b) ray Fig. 3.1 (a) Refraction of light as it passes from air to glass (b) Refraction of light as it passes from glass to air Where does light travel fastest? The speed of light is different in almost transparentmaterial. In a vacuum the speed of light is about 3.0 x 108 m/s, and in water the speed is1.88 x 108 m/s. The ratio of the speed of light in a vacuum to its speed in another substanceis called the absolute index of refraction, n, for that substance.Remember This Index of refraction = Speed of light, c Speed of light in a given substance, v n= c v So, if you know the index of refraction of a substance you can determine the speed oflight in that substance. Also, the higher the index of refraction, the slower the speed of light in the substance.This means that the higher the optical density of a substance, the higher is its index ofrefraction.Table 3.1 shows the index of refraction of some substances. Table 3.1 Index of Refraction Substance Index of Refraction, n Air 1.0003 Glass, crown 1.52 Glass, float 1.63 Water 1.33 Diamond 2.42 13

Do you know what is the importance of the index of refraction? The index ofrefraction of a pure, transparent substance is a constant quantity which is a definite physicalproperty of a substance. Hence, the identity of a substance can be determined bymeasuring its index of refraction. The very high index of refraction of diamond provides apositive test for its identification.Laws of Refraction The facts about refraction of light maybe summarized in three laws of refraction. 1. The incident ray, the refracted ray, and the normal to the surface at the point of incidence are all in the same plane. 2. The index of refraction for a particular substance is always a constant. 3. When a ray of light passes at an angle from a medium of lesser to one of greater optical density, it is bent toward the normal. Conversely, a ray of light passing at an angle from an optically denser medium to a lesser medium is bent away from the normal ray.Total Internal Reflection You already learned that as a ray of light passes from a medium of higher opticaldensity (water) into one of a lower optical density (air) it is bent away from the normal. Asthe angle of incidence continues to increase, a value is finally reached at which the angle ofrefraction equals 90o and the refracted ray does not enter the air at all but takes the pathalong the water surface. The angle of incidence in the denser medium resulting in angle ofrefraction of 90o is called the critical angle ic. (Figure 3.2) If the angle of incidenceexceeds the critical angle total internal reflection occurs. normal refracted normal ray ray ray r r = 90oair airwater waterincident i ic r reflectedray ic ray incident i>ic (a) ray (b) Fig. 3.2(a) The critical angle is the angle of incidence in the denser medium which results in a 90o angle of refraction.(b) Total internal reflection occurs when the angle of incidence exceeds the critical angle. 14

Remember This If the angle of incidence of a ray of light passing from water into air is increased beyond the critical angle, no part of the incident ray enters the air. It is totally reflected from the water surface. Total internal reflection occurs when the angle of incidence exceeds the critical angle. Do you know why diamond is a very brilliant gem? It is because its index ofrefraction is high and its critical angle is very small. Very little of the light that enters a cutdiamond passes through it. Most of the light is reflected internally. Fiber optics makes it possible to use light instead of electricity to transmit messagesby total internal reflection. Optical fibers are also used in the field of medicine. An endoscope is an instrumentused to explore the inside of the human body using the principle of total internal reflection.Lenses What are lenses made of? Lenses are made of transparent substance like glass orplastic which can bend light rays. Lenses are of two kinds: a. Converging lens (convex) which is thicker at the middle than at the edge b. Diverging lens (concave) which is thicker at the edge than at the middledouble plano- converging double plano- divergingconvex convex meniscus concave concave meniscus (a) Converging lenses (b) Diverging lensesFig. 3.3 Lens shapes How do lenses refract rays of light? When light rays parallel to the principal axis pass through a converging lens, the raysare refracted toward the thicker part of the lens, and they all converge at a point called the 15

real focus. However, parallel rays of light are spread out by a diverging lens and appear tomeet at a virtual focus. virtual focus real focus FF a. converging lens b. diverging lensFig. 3.4 Lenses refract parallel rays so they meet at the principal focusLens Terminology What are the different terms related to lenses? Spherical lenses usually have twocenters of curvature which are the centers of the intersecting spheres which form the lenssurfaces. The centers are shown in Figure 3.5 as points C and C’. In lenses, the focus is not midway between the lens and the center of curvature aswe found to be in spherical mirrors. Its position on the principal axis depends on the indexof refraction of the lens. With a double convex lens of crown glass the principal focusalmost coincide with the centers of curvature, thus the radius of curvature and the focallength are almost equal.1. Optical center, O – the center of the lens s2. Principal axis, P – line joining the centers C O C’ rfof curvature and passes through the Foptical center P Figure 3.53. Secondary ray, S – ray passing throughthe optical center but not parallel to theprincipal axis4. Focal length, f – the distance betweenthe focus and the optical centerRay Method of Image Formation in Lenses How can we locate the image of an object formed by a lens? Lenses form images byrefraction. To locate the image, use the following rays coming from point A on the object:(see Figure 3.6) Ray 1 is an incident ray parallel to the ray 1 principal axis and is refracted through the focus. object ray 2 Ray 2 is an incident ray along the 2F F O F’ 2F’ secondary axis which is not appreciably refracted as it passes through the image optical center (O) of the lens. Figure 3.6 16

Image Formation in a Convex Lens Using the ray method let us construct, locate and describe the images formed by athin converging lens at different positions of the object from the lens. Study Figure 3.7.Fig. 3.7 Image at Different Positions of the Object from the Lensa. Object is at infinite distance b. Object is beyond twice the focal length (2F) F A ray 1 O object ray 2 2F F O F’ 2F’ imageThe image is a point at the principal focus. Image is real, inverted, diminished and located between F’ and 2F’.c. Object is at twice the focal length (2F) d. Object is between 2F and F A ray 1 O F’ 2F’ A ray 1 O F’ 2F’object ray 2 image object ray 2 image 2F F 2F F Image is real, inverted, of the same size and Image is real, inverted, bigger and located located at 2F’. beyond 2F’.e. Object is at the focus (F) f. Object is between the focus and the optical center A ray 1 F’ 2F’ image F’ 2F’ object A ray 2 object2F F O 2F F ORefracted rays are parallel. No image is Image is virtual, erect, bigger and located formed. between 2F and F. 17

Image Formation in a Concave Lens A ray 1 F’ 2F’ What kind of image is formed by a object ray 2concave lens? The ray method shown in Figure3.8 shows the image formed by a concave lens. 2F F imageIt is always erect, virtual and smaller in size. Figure 3.8 Image in a concave lensThe Lens Formula The equation used to determine the object distance do, image 1= 1 + 1distance di and the focal length f for spherical mirrors also applies for f do dilenses. Hence, the lens formula is the same as the mirror formula.The size rule for mirrors also applies for lenses. si = di so doFor numerical computations, the following sign conventions are followed: Lens f do diconvex (converging)real image +++virtual image ++ -concave (diverging)virtual image -+- The focal length is positive for a converging lens and negative for a diverging lens.Object distance is positive for both converging lens and diverging lens. Image distance ispositive for real images and negative for virtual images.Study ThisSample problem: An object 8 cm tall is placed 30 cm from a converging lens. A real image is formed 15 cm from the lens. a) What is the focal length of the lens? b) What is the size of the image? Describe the image. 18

Given: so = 8 cm Solutions: b) do = 30 cm a) Si = di di = 15 cm 1= 1 + 1 So do f do di Si = So diFind: a. f 1= 1 + 1 b. si f 30 cm 15 cm do 1 = 1+ 2 Si = 8 cm x 15 cm f 30 cm 1= 3 30 cm f 30 cm Si = 4 cm 3f = 30 cm Image is smaller f = 30 cm 3 than the object f = 10 cm What you will do Self-Test 3.1Direction: Completion Type. Write the word or expression which best completes the meaning of the following statements.1. __________ is the bending of light as it passes at an angle from one medium into another of different optical density.2. The angle between the refracted ray and the normal drawn to the point of refraction is called __________.3. __________ is the ratio of the speed of light in a vacuum to its speed in a given substance.4. The index of refraction for any two media is always equal to a __________.5. When a ray of light passes at an angle from a medium of lesser to one of greater optical density, it bends __________ from the normal.6. The limiting angle of incidence in the denser medium resulting in angle of refraction of 90o is known as __________.7. The distance between the principal focus and the optical center of the lens is __________.8. __________ is the kind of lens that will always form a virtual, erect and smaller image.9. The principle involved in the formation of image on lenses is __________.10. An enlarged, erect and real image is formed by a __________ lens. Key to answers on page 30 19

Lesson 4 Color, Interference and Polarization of Light Have you ever wondered why the sky appears blue during noontime and reddish atsunset? Why do we see rainbow colors in soap bubbles or in thin films with oil? How arerainbows formed? What is color? What you will do Activity 4.1 DispersionHold a prism or a bottle half-filled with water against sunlight or any light source like aflashlight.Answer these: 1. What do you observe? 2. Enumerate the colors you observe. Key to answers on page 31Colors of Light When light leaves the prism and i red redstrikes a white screen, it separates into violet orangespectral colors. Dispersion is the white yellowseparation of white light by a prism light greeninto bands of colors – red, orange, blueyellow, green, blue and violet. Thespectrum is due to the difference in the violetvelocities and wavelength of thespectral colors. Violet is bent most Fig. 4.1 Dispersion of light by a prismand is slowed down more than the redlight.Dispersion of light shows that light is a mixture of different spectral colors. 20

Know This violet Have you seen a rainbow? When redcan you see a rainbow? Fig. 4.2 A rainbow is a spectacular display of Comparison of wavelengthscolors. We usually observe a rainbow aftera rainshower. The raindrops act as prism of red and violet lightseparating sunlight into bands of colors. Arainbow is produced by reflection, refractionand dispersion of light when sunlight strikesdrops of falling water which act as prisms.The difference between one color andanother is due to difference in wavelengthsor frequencies. Each color of light has itsown wavelength and frequency. Violet has ahigher frequency but shorter wavelength.Red has a lower frequency but longerwavelength (see Figure 4.2).Colors of Object Why do objects show colors? Objects show colors because they reflect one or moreof the colors present in the white light. The color of an object depends on the wavelength oflight that it reflects. A camia flower appears white because it reflects all the colors of light it receives. Apiece of coal appears black because it absorbs all the colors that fall on it. Under ordinarydaylight a blue bird appears blue because it absorbs all other colors and reflects only blue.Why does a red rose appear red? The rose appears red because it reflects mainly red colorand absorbs all other colors. Think of This Suppose the light falling on an object you are looking at is not white. What do you think will happen? For example, a blue book under a red light will appear black because it absorbs the red light and no color is reflected in our eyes. Similarly, when a green light falls on a red book, the book will also appear black because it absorbs the green light. No color is reflected to our eye. How will a green book appear under a blue light?21

red light green light blue light blue red green book book bookblack black ? Fig. 4.3Colored light falling on colored objects What you will do Activity 4.2 Diffraction of Light1. Look at the light through a slit between your fingers. What do you observe? Do you see vertical white and dark bands? What causes the bands?2. Repeat step 1 but make the slit narrower. What happens when the slit becomes narrower? Know This As you look at the light through one slit between your fingers you observe thin vertical white and dark bands. This is because of the bending or spreading out of light after passing through the opening. The bending of light as it passes through an obstruction such as a small slit is called diffraction. As the slit becomes narrow, diffraction patterns become more prominent.Scattering of Light Do you know why the sky is blue during noontime? Why is the sky red at sunset? When sunlight shines down on the atmosphere, the dust particles or molecules in theatmosphere scatter the light in all direction. The amount of scattering of light depends on 22

the wavelength of the light. During noontime, most of the blue light of shorter wavelength insunlight is scattered and reflected to earth, so the sky looks blue. At sunset, the light travelslonger distances with more air and dust in the atmosphere. Thus, most of the blue light isabsorbed before it reaches you. Therefore, red light which has a longer wavelength is themost predominant color left when the light from the sun reaches the eye. Hence, the sunsetappears red. What you will do Activity 4.3Get a basin with soap suds. Blow on the soap suds. What can you observe in the soapbubbles?Interference of light Have you noticed the beautiful spectrum of colors reflected from a soap bubble?These colors are produced by the interference of light wave. This is often callediridescenes and is observed in the transparent film. When light strikes the outer surface of atransparent material like a soap bubble, part of the lightis reflected and part of the light enters the insidesurface. At the inside surface, some of the light isreflected again. The two reflected beams returningtoward your eye may have a path difference that isdetermined by the thickness of the film. If the lightwaves are in phase, they interfere constructively andproduce a bright fringe. If they are out of phase, theyinterfere destructively and produce a dark band. Ifwhite light is incident on the thin film, light of differentwavelengths (colors) constructively interfere in differentregions, giving rise to the rainbow-colored appearanceof the film. Thomas Young (1801) was the first to Fig. 4.4 Interference of lightdemonstrate interference of light using two slits. Waves in soap bubblesfrom a monochromatic light source are made to passthrough two narrow slits, S1 and S2 (Figure 4.5). 23

Fig. 4.5 Interference of light using two slits According to Huygen’s principle, these slits are sources of secondary waves. Oneslit spreads out the light and produces its own wave. The other slit also diffracts the light,producing another wave. These waves produced in S1 and S2 are of the same wavelengthand in phase with the initial light source. When the light waves from S1 and S2 meet atpoint P0 in phase, wave crests meet wave crests and troughs meet troughs, constructiveinterference occurs, producing a bright area. Light waves from two slits may be completely out of phase when they meet at a pointP1, that is, a crest meets a trough. In such a case, destructive interference occurs,producing a dark area.Polarization Think of This What is polarized light? Imagine a wave produced from a rope tied to a post (Figure 4.6). The rope is inserted through the vertical slits of two sheets of cardboard and waves are produced by moving the free end up and down. Waves pass through the slits when the slits in both cardboards are vertical. The waves are said to be plane polarized. All vibrations are in one plane, the vertical plane. When the slits in one cardboard are placed horizontally, they do not allow waves to pass through. 24

Ordinary light vibrates in all directions. It is unpolarized. When this light is allowed to pass through a filter called Polaroid, the light vibrates only in one plane (Figure 4.7). It comes out as polarized light. What happens when light is allowed to pass through two Polaroid sheets? Light is transmitted when the axes of the Polaroid sheets are parallel. Light, however, is not transmitted when the axes of the polaroid sheets are perpendicular (Figure 4.8). What does this show about light? Light is a transverse wave.Fig. 4.6A mechanical analogy of polarizationFig. 4.7 Fig. 4.8Polarized light from a polaroid sheet Light is not transmitted when axes of the polaroid sheets are perpendicular One application of polarization is the reduction of glare using polaroid sunglasses.Bright light reflected from a road or water surface is scattered in all directions. The polaroidsunglasses absorb the horizontal vibrations of the light, and hence reduce the glare. 25

What you will do Self-Test 4.1Directions: Identify the term defined, described or referred to in the following.____________ 1. The process of separating light into a band of colors____________ 2. The bending or spreading out of light through small openings or around corners____________ 3. Light in which vibrations occur in a single plane perpendicular to the ray____________ 4. The property of light waves which is dependent on the frequency or wavelength of radiation that reaches the eye____________ 5. The superposition of 2 beams of light resulting in a loss of energy in one area and a reinforcement of energy in others____________ 6. The band of colors when sunlight is dispersed by a prism____________ 7. The color which is refracted most when sunlight is separated by a prism Key to answers on page 31Let’s Summarize1. The laws of reflection state that: a. The incident ray, reflected ray, and the normal to the reflecting surface all lie in the same plane. b. The angle of incidence is equal to the angle of reflection.2. Images in mirrors are formed by reflection.3. The size of an object and the size of its image are related to their distance fromthe mirror and are related to the focal length of the mirror. This relationship isgiven by the equations1 = 1 + 1 and Si = dif do di So do4. Refraction is the bending of light rays as they pass at an angle from one medium to another with a different optical density.5. The index of refraction for a particular medium is a constant that is independent of the angle of incidence.6. The limiting angle of incidence in the denser medium, resulting in an angle of refraction of 90o is known as the critical angle. 26

7. Total internal reflection occurs when the angle of incidence exceeds the critical angle.8. Converging lens is a lens that is thicker in the middle than at the edges and refracts parallel rays passing through it to a focus.9. Diverging lens is a lens that is thinner in the middle than at the edges, causing parallel rays passing through it to diverge as if from a point.10. Lenses form images by refraction.11. Dispersion is the process of separating white light into a band of colors.12. Diffraction is the bending of light as it passes through a small opening.13. The color of light is dependent on the frequency or wavelength of the radiation that reaches the eye.14. The color of an opaque object depends on the kind of light it reflects to the eye. It also depends on the color of light incident on it.15. Interference of light occurs when two beams of light superimposed with one another.16. Polarization of light depends on the transverse nature of light waves – that is, light vibrates only in one plane.PosttestMultiple Choice. Choose the letter of the best answer.1. The theory that explains light as a particle.a. corpuscular theory c. quantum theoryb. electromagnetic wave theory d. wave theory2. When we see a tree, the light that reaches our eyes a. has been reflected by the tree. b. has been refracted by the tree. c. has been separated into a spectrum by the tree. d. has undergone interference in passing through the tree. 27

3. Enlarged image can be formed by c. either concave or convex mirror a. concave mirrors only d. neither concave nor convex mirror b. convex mirrors only4. The image formed by a convex mirror is alwaysa. real c. bigger than the objectb. inverted d. smaller than the object5. If you are looking obliquely on a fish under water, in what direction should you aim yourarrow to hit it?a. above the fish c. directly to the fishb. below the fish d. either below or above the fish6. The term refraction refers to a. the bending of light rays when they strike a mirror. b. the bending of light rays when they enter a different medium. c. the fact that white light is made up of many colors. d. the fact that light travels in straight line in uniform medium.7. As the angle of incidence increases, the index of refraction of a mediuma. increases c. remains unchangedb. decreases d. none of the above8. If you look down on a pool of still water, you see your face clearly. Which one of the following gives the best explanation for this observation? a. Dispersion of light on entering water b. Reflection of light by the surface of the water c. Refraction of light by the surface of the water d. Light is reflected from the surface of the water in different directions.9. A diamond is a brilliant gem because c. most of the light is refracted. a. it has low index of refraction. d. most of the light is reflected internally. b. it has big critical angle.10. A ray of light is reflected from a plane mirror. The angle of incidence is 20o. The anglebetween the incident and the reflected ray isa. 10o c. 30ob. 20o d. 40o11. When you stand 3 m in front of a full length mirror, your image isa. real and 1 m behind the mirror c. virtual and 2 m behind the mirrorb. real and 3 m behind the mirror d. virtual and 3 m behind the mirror12. The bottom of a clear and deep lake appears to be shallow because of ____________a. diffraction c. reflectionb. polarization d. refraction 28

13. When sunlight strikes raindrops, it passes through them and producesa. halo c. rainbowb. heat d. shadow14. Side mirrors of motor vehicles allow the driver to see wider areas. What best describesthe images compared to the real object in this kind of mirror?a. bigger c. the sameb. smaller d. inverted15. What do you call the separation of light into its component colors?a. dispersion c. reflectionb. polarization d. refraction16. Where does light travel fastest? c. vacuum a. air d. water b. glass17. What do you call the bending of light around the corners of objects?a. diffraction c. reflectionb. dispersion d. refraction18. A beam of light traveling in air enters a glass medium. What changes does it undergo?a. change in speed only c. change in wavelength onlyb. change in frequency only d. change in both speed and wavelength19. Which is the color of visible light with the longest wavelength?a. blue c. violetb. red d. yellow20. Which of the following is a good description of a polarized light? a. It is an ordinary light. b. It is a transverse wave. c. It is a longitudinal wave. d. It is a wave that vibrates in all directions. Key to answers on page 31 29

Key to AnswersPretest1. a 6. b 11. d 16. a2. c 7. d 12. a 17. d3. d 8. d 13. a 18. b4. b 9. d 14. a 19. b5. a 10. b 15. a 20. aLesson 1Self-Test 1.11. b2. d3. a4. cLesson 2Self-Test 2.11. real image 6. beyond the center of curvature2. angle of incidence 7. at the focus3. convex mirror 8. vertex4. focal length 9. convex mirror5. plane mirror 10. concave mirrorLesson 3 6. critical angle 7. focal lengthSelf-Test 3.1 8. concave lens 9. refraction1. refraction 10. convex lens2. angle of reflection3. index of refraction4. constant5. towards 30

Lesson 4Activity 4.11. spectral colors2. red, orange, yellow, green, blue, violetSelf-Test 4.11. dispersion2. diffraction3. polarized light4. color5. interference6. spectral colors7. violetPosttest1. a 6. b 11. d 16. c2. a 7. c 12. d 17. a3. a 8. b 13. c 18. d4. d 9. d 14. b 19. b5. b 10. d 15. a 20. bReferencesHewitt, P. G. (1993). Conceptual physics. (7th ed). New York: Harper Collins College Publishers.Padua, A. L. & Crisostomo, R. M. (1999). Science and technology IV: Physics. Quezon City: S.D. Publications, Inc.Santos, G. C. & Ocampo, J. P. (2003). Science and technology IV: Physics. Manila: Rex Bookstore, Inc.Sotto, R. L. (2005). Science in today’s world: Physics. Makati: SIBS Publishing House, Inc.Young, H. D. & Friedman, R. A. (1996). University physics. New York: Addison Wesley Publishing Co., Inc. 31

Module 4 Optical Instruments What this module is about In the previous modules, you learned about the properties of light. You also learnedhow images are formed by mirrors and lenses. Now it is time to apply these ideas to somecommon optical lenses and to show how such devices work. In this module you will study different optical instruments in the following lessons:  Lesson 1 – The Human Eye and the Camera  Lesson 2 – Microscopes and Telescopes  Lesson 3 – Laser and Holography What you are expected to learn After going through the module you are expected to: 1. identify the parts of a human eye; 2. discuss the different eye defects and how lenses correct these defects; 3. compare the similarities and differences between the principle of the camera and the human eye; 4. show using ray diagrams how images are formed in a telescope and a microscope; and 5. explain the principle of a hologram. How to learn from this module Here is a simple guide for you in going through the module: 1. Read and follow the instructions carefully 2. Answer the pretest before you start the lessons. 3. Check your answers against the key to answers provided at the last page of the

module.4. After taking the pretest, read and study carefully the different lessons on optical instruments.5. Perform all the activities to have a better understanding of the topic.6. Take the self-tests at the end of each lesson for you to determine how much you learn and remember about the lesson.7. Take the posttest prepared at the end of the module for you to assess how much you learned from this module. Have fun in learning these lessons about optical instruments! Good luck!What to do before (Pretest)A. Multiple Choice: Write the letter of the best answer.1. Which part of the human eye refracts rays and forms the image of an object?a. cornea c. lensb. iris d. retina2. A camera forms an image in a sensitive film while an eye forms the image on thec. cornea c. pupild. iris d. retina3. Which statement about the parts of the eye and their uses is FALSE? a. The eyelid opens or shuts the eye. b. The iris enables the eye to see nearby objects. c. The pupil controls the intensity of the incoming light. d. The retina serves as the screen where the image is formed.4. A farsighted person needs a convex lens as this lens can make the image falla. on the eyeball c. on the retina of the eyeb. before the retina of the eye d. beyond the retina of the eye5. What can a camera do which a human eye cannot do? a. It can form images of object. b. It can adjust to dim and bright lights. c. It can change focus from short to long distances. d. It can give a permanent record of the scene on which it is focused. 2

6. Which of the following optical instruments does NOT form a real, inverted and smallerimage?a. camera c. pinhole camerab. human eye d. simple microscope7. An optical device used to see very far or distant objects clearly is thea. camera c. simple microscopeb. compound microscope d. telescope8. A compound microscope is an optical system. Which statement does NOT describe it? a. It makes small objects look bigger. b. It is used to magnify distant objects clearly. c. It consists of two converging lens - an objective lens and an eyepiece. d. It has an eyepiece that enlarges the image created by the objective lens.9. A simple microscope produces c. an erect and real image a. an enlarged and real image d. an erect and smaller image b. an enlarged and virtual image10. Which describes a hologram? a. It is a recording of an image. b. An ordinary light is needed to make a hologram. c. It forms a true three-dimensional image of the object. d. It is a photographic record of only one view of the object.B. Identify the terms or phrases referred to in the following.____________ 1. The part of the eye where the image of an object is formed____________ 2. The part of the camera which corresponds to the iris of the eye____________ 3. The kind of lenses used to correct nearsightedness____________ 4. The ability of the eye to adjust the shape of its lens in order to focus on objects at different distances____________ 5. An eye defect which focuses the image beyond the retina____________ 6. A lens prescribed to correct presbyopia____________ 7. An optical device that forms magnified virtual and erect image____________ 8. An optical device to magnify very distant objects____________ 9. An optical system consisting of two converging lenes that magnifies a magnified object____________ 10. A technique to reproduce image through interference effect Key to answers on page 19 3

Lesson 1 The Human Eye The eye is the most remarkable optical instrument. What are the parts of the humaneye? The eye is spherical in shape and is about 2.5 cm in diameter. The essential parts ofthe human eye, considered as an optical system, are shown on Figure 1.1.1. The white coat or sclera is the hard, tough outer coat of the eyeball which maintains the shape of the eyeball and protects the eyes. The transparent cornea in front of the sclera admits light into the eyeball. The region behind the cornea is a liquid called aqueous humor.2. The middle coat or choroids Fig. 1.1 The structure of the eye layer contains a black pigment, whose function is to absorb stray rays of light and prevent the blurring of images.3. The inner coat, or retina covers only the rear portion of the eyeball. The nerves of the eyes spread through the retina, forming a light sensitive screen to receive images. Structures in the retina, known as rods, enables us to see in the dark.4. The crystalline lens is a double convex lens that forms a real, inverted and smaller object on the retina. (Figure 1.2)5. In front of the lens is the iris, Fig. 1.2 Image formed in a human eye which serves as a diaphragm to regulate the amount of light entering the inner eye.6. The pupil is the opening in the center of the iris. In a dark room the pupil becomes larger to admit more light, in bright sunlight it becomes smaller reducing the amount of light admitted thus protecting the retina from damage by exposure to intense light.7. Behind the lens, the eye is filled with a thin watery jelly called vitreous humor. 4

8. The eyelids act as shutters to screen out the light and, in general, to protect the eye. What you will do Activity 1.1 Identify Parts of an Eye Look at the eye of another person. Identify the parts of the eye that you can see. Key to answers on page 19How does the eye focus? For an object to be seen clearly or sharply, the image must be formed exactly on theretina. To see objects at different distances, the eye adjusts itself by changing the shape ofits lens. If the object is near, the image distance increases and the lens become rounderand thicker. Its focal length is shortened so that the image distance is kept constant and theimage is kept on the retina. If the object is far, the image distance decreases such that the muscles attached tothe outer edges of the eye lens cause the lens to become thinner and flatter. This increasesits focal length and enables the image to be focused sharply on the retina. This ability of the eye to focus the image of an object at different distances is calledthe power of accommodation. When the eye muscles are perfectly relaxed as when a person is looking at a distantobject, the lens has its greatest focal length and is said to be adapted to the far point. Whenthe object is so near that the lens has its shortest possible focal length, the object is said tobe at the near point. For a normal eye, the shortest distance for distinct vision is 25 centimeters. The lensmuscles are completely relaxed when we look at objects more than 6 meters away.Common Eye Defects When the eye loses its ability to change the shape of its lens, vision becomes poorand defective. Properly chosen eye glasses are needed to correct these eye defects. 5

1. Nearsightedness or myopia A nearsighted person or myope can see near objects clearly but has difficulty focusing on far objects. This occurs when you have a long eyeball and lenses that are too convex, causing the image to be formed in front of the retina. Eyeglasses with concave lenses are prescribed to correct nearsightedness. Study figure 1.3 which shows image formation in a nearsighted individual and how it is corrected by a concave lens. Fig 1.3 A concave lens may be used to correct nearsightedness.2. Farsightedness or hyperopia A farsighted person or hyperope can see very far objects clearly but has difficulty focusing on near objects. This is due to having a short eyeball and too flat lenses that cause the image to be formed beyond the retina. Eyeglasses with convex lenses are prescribed to correct farsightedness. Study figure 1.4 which shows the image formation in a farsighted individual and how it is corrected by a convex lens. Fig. 1.4 A convex lens may be used to correct farsightedness. 6

3. Presbyopia For an older person, the power of accommodation is reduced due to the decrease in the elasticity of the lens and the lessened ability of the eye muscle to increase the roundness of the lens. This inability is called presbyopia. To remedy this, bifocal lenses are usually prescribed.4. Astigmatism The unevenness in the curvature of the lens of the eyeball causes astigmatism which results in blurred vision and headaches. An astigmatic person will see horizontal and vertical lines not equally distinct and clear. This is usually corrected with cylindrical lenses. Fig 1.5 The lines are not all equally distinct if the eye is astigmatic.The Camera and the Eye Your eyes enable you to see the color and beauty of things around you. Sometimesyou do not like to leave and forget such sights. To have an exact and permanent record ofthem, you use a camera. A good way to find out how a camera works is to make a simple one.What you will doActivity 1.2 A Pinhole CameraMaterials: empty powdered milk can (11 cm long and 10 cm in diameter) small nail and hammer black cartolina (about 35 cm x 30 cm) tape or paste wax paper, about 14 cm2Procedure:1. Get a milk can and remove its cover. Make a tiny hole in the center of its bottom using a small nail and hammer. (Figure 1.6a) 7

2. Make a tiny tube out of the black cartolina. The tube must fit into the can. Cover one end of the tube with wax paper. (Figure 1.6b)3. Slide the covered end of the black tube into the can. You now have a pinhole camera. (Figure 1.7)4. Point the pinhole to a distant object such as a building or tree. View this object through the open end of the black tube. Move the tube to get a clearer view of the object on the wax paper. The wax paper serves as the screen for the camera. Fig. 1.7 Fig. 1.6Answer these:1. What is formed on the wax paper? __________________________________________2. Compare what you see on the wax paper with the object to which the camera is pointed. (Figures 1.8) ___________________________________________________________ ______________________________________________________________________ Fig. 1.8 A pinhole camera Key to answers on page 19 The real camera has a lens instead of a pinhole and uses a film for a screen insteadof a wax paper. 8

The basic elements of a camera are, namely: a converging lens, a light sensitive filmto record an image, and a shutter to let the light from the lens strike the film. The lens formsan inverted, real and smaller image in the film. Figure 1.9 The formation of an image in a camera. When the camera is in proper focus, the position of the film coincides with theposition of the real image formed by the lens. With a converging lens, the image distanceincreases as the object distance decreases. Hence in focusing the camera, the lens ismoved closer to the film for a distant object and farther from the film for a nearby object.Often, this is done by turning the lens in a threaded mount. Know This: A camera is similar to a human eye in several aspects. The shutter of a camera excludes unnecessary light just as the eyelids do. The diaphragm regulates the amount of light that enters the camera through the aperture just as the iris regulates the amount of light that enters the eye through the pupil. In the dark, the pupil dilates, while it constricts in bright light. A camera has a simple converging lens or a system of lenses which forms images by refraction just like the lens of a human eye. The light sensitive film inside a camera corresponds to the light sensitive retina in the back of the eye, and both receive an inverted, real image that is smaller than the object. In a camera, the lens is adjusted to form a sharp image, while our eyes have the power of accommodation to see near and distant objects. The camera gives a permanent image of the object, while the image in the eye lasts for only about 1/16 of a second before another distinct image is formed. Source: Science in Today’s World Series: Physics, 2005, pp. 231-232. 9

What you will doSelf-Test 1.1A. Fill up the blanks in Table 1.1 which gives the similarities between a camera and a human eye in terms of their parts and functions. Table 1.1 Similarities between a Camera and a Human Eye Parts FunctionsCamera Human Eyea. shutter _____(1)______ Protects, opens and closes the eyeballs tob. diaphragm exclude unnecessary light _____(2)______ _______________(3)________________c. ____(4)_____ pupil Opens and closes to control the intensityd. ____(5)_____ lens of the entering light _______________(6)________________e. film _____(7)______ Serves as screen where the image is formedB. Answer this: Give two differences between a camera and a human eye.1. _________________________________________________________________2. _________________________________________________________________ Key to answers on page 20Lesson 2 Microscope and Telescopes Most optical instruments are made up of a lens or an arrangement or combination oflenses. The function of the optical systems is determined by the focal lengths of the lensesand their relative positions. 10

What you will do Activity 2.1 Open your book. Get a magnifyingglass. Hold it close to a page on a book.Vary the distance of the lens until you see aclear magnified image of the printed words.Magnifying Glass: A Simple Microscope The simple use of a converging lens is a magnifying glass. When we use amagnifying glass, we hold it very close to the object we wish to examine. This is because aconverging lens produces an enlarged and erect image when the object is inside its focalpoint. If a screen is placed at the image distance, no image appears on it because no lightis directed to the image position. The rays that reach our eye, however, behave virtually asif they came from the image position, so we call this a virtual image. A diverging lens used alone Fig. 2.1produces a reduced virtual image. It Ray diagram of image formationmakes no difference how far or hownear the object is. When a diverging in a simple magnifierlens is used alone, the image is alwaysvirtual, erect and smaller than theobject. A diverging lens is often used asa “finder on a camera”. When you lookat the object to be photographedthrough such a lens, you see a virtualimage that approximates the sameproportion as the photograph. 11

Compound Microscope (a) (b) Fig. 2.2 (a) Elements of a compound microscope; (b) Ray diagram of image formation in a compound microscope A compound microscope makes a small object look bigger so that our eye can see it.A compound microscope consists of two converging lenses of short focal lengths: theobjective lens and the eyepiece lens. The object is placed close to the focal point of theobjective lens to form the first image, which is an enlarged, real and inverted image. Thisimage falls between the eyepiece lens and its focus and becomes the object for theeyepiece lens. The eyepiece forms a final virtual and enlarged image at a distance of 25cm for distinct vision. This final image in the microscope becomes the object for the eyewhich forms a real image on the eye’s retina.Telescope A telescope is used to make distant objects look closer and appear bigger. Itconsists of two converging lenses: the objective lens with a long focal length and theeyepiece lens with a short focal length. The objective lens is used to collect light from adistant object and to form the first image. The eyepiece lens is a magnifying lens whichproduces a final virtual image at a distance. 12

The optical system of a telescope is similar to that of a compound microscope. Inboth instruments, the image formed by an objective lens is viewed through an eyepiece.The key difference is that the telescope is used to view large objects at large distances andthe microscope is used to view small objects at a very close distance. An astronomical telescope is a telescope that uses lens as an objective. It is called arefracting telescope. In the reflecting telescope the objective lens is replaced by aconcave mirror. Fig. 2.3(a) A telescope; (b) Ray diagram of image formation in an astronomical refracting telescopeWhat is a Hubble Space Telescope? The Hubble Space Telescope (HST) is not onlya telescope with scientific instruments. It is also aspacecraft and has power to move in orbit. A HSTenables astronomers to look out at a distant star ornebula with amazing clarity. With such telescope youcould peer billions of light years away and see thingsthat happened billions of years ago.The space telescope was named afterAmerican astronomer Edwin Hubble, whoseobservation of variable stars in distant galaxiesconfirmed that the universe was expanding and gavesupport to the “Big Bang Theory”. Fig. 2.4 Hubble Space Telescope http://science.howstuffworks.com/hubble.htm 13

What you will do Self-Test 2.1Identify the terms or phrase referred to in the following:____________ 1. It consists of a converging lens that forms virtual, magnified and erect image.____________ 2. It is a lens system which makes distant objects appear bigger and closer.____________ 3. It is a lens system which makes a small object look bigger.____________ 4. It is a lens in a telescope used to collect light from a distant object to form the first image.____________ 5. It is the lens in a telescope which serves as a magnifying lens producing a virtual image. Key to answers on page 20Lesson 3 HolographyWhat is a hologram? Holography is a technique for recording and reproducing an image of an objectthrough the use of interference effects. Unlike the two-dimensional images recorded by anordinary photograph or television system, a holographic image or hologram is truly three-dimensional. Do you know? The hologram was invented and named by Dennis Gabor in 1947. Holo in Greek means “whole” and gram in Greek means “message” or “information”. A hologram contains the whole message or entire picture.How does a holograph differ from a photograph? In ordinary photography, a lens is used to form an image of an object in photographicfilm. Light reflected from each point on the object is directed by the lens on the film. In thecase of holography, no image-forming lens is used. Instead, each point of the object being“photographed” reflects light to the entire photographic plate, so every part of the plate isexposed with light reflected from every part of the object. Most importantly, holograms aremade with laser light which is a coherent light. 14

A conventional photograph is a recording of an image, but a hologram is a recordingof the interference pattern.How is hologram made? The basic procedure for making a hologram is shown in Figure 3.1. The object to beholographed is illuminated by a laser light. LASER is the acronym for “light amplification bystimulated emission of radiation”. Part of the light is reflected from the object to aphotographic plate. The rest of the light, called the reference beam, is reflected by a mirrorto the same plate. The two wavefronts interfere, and the interference pattern recorded onthe plate constitutes the hologram. An example of a hologram is the silver sticker on an original VCD used to identify ifthe VCD is pirated or not. Another hologram is the sticker at the back of the original batteryof a cellular phone. Figure 3.1 Principle of HolographyWhat are some uses of holograms? Holograph systems are used with laser beams to scan the universal bar codes ongrocery store items. Holograms have many other possible uses. They can storetremendous amount of data in a limited space, give details of structural flaws in a machineparts, display the interior of body organs, and bring three-dimensional television picturesinto your home. 15

What you will doSelf-Test 3.1A. Multiple Choice: Write the letter of the best answer.1. It is a technology that uses laser light to produce a three-dimensional image of an objector scene.a. photography c. stenographyb. holography d. x-ray2. What kind of light is needed in hologram?a. ordinary light c. coherent lightb. neon light d. incoherent light3. Who invented the first hologram? c. Dennis Gabor a. Gottfried Leibnitz d. Robert Brown b. Thomas Edison4. The following are applications of holography EXCEPT one: a. scanning of universal bar codes on grocery items b. storing tremendous amount of data in a limited space c. displaying the interior of body organ d. locating criminals5. A hologram contains the whole message or entire picture.a. True b. FalseB. Give the differences between a photograph and a hologram. ____________________________________________________________________________________________________________________________________________ Key to answers on page 20Let’s Summarize1. The most important parts of the eye are the: a. eyelid – opens and shuts the eye b. iris – regulates amount of light entering the eye c. pupil – opens and closes to control intensity of entering light d. lens – refracts light to form images 16

e. retina – serves as a screen where the image is formed2. A nearsighted individual can see near objects clearly but has difficulty focusing on far objects. Nearsightedness is corrected with a concave lens.3. A farsighted individual can see far objects clearly but has difficulty focusing near objects. Farsightedness is corrected with eyeglasses with convex lens.4. Astigmatism is due to unevenness in the curvature of the lens of the eyeball which results to blurred vision. It is corrected with cylindrical lenses.5. Presbyopia is the inability of the eye muscles to increase the roundness of the lens, thus reducing its power of accommodation. Bifocal lens is prescribed to remedy this defect.6. A camera and a human eye both form real, inverted and smaller images of objects.7. A camera can produce a permanent record of an image while eyes do not.8. In a camera, the lens is adjusted to form a sharp image while the eyes has the power of accommodation to see near or far objects.9. A simple microscope consists of a single lens which produces a magnified, virtual and erect image.10. A compound microscope consists of two converging lenses. It is used to view small objects at a very close distance.11. A telescope is used to view large objects at very far distances. a. A refracting telescope uses a lens as an objective. b. A reflecting telescope uses a concave mirror as an objective.12. Holography is a technology that uses laser light to produce a three-dimensional image of an object or scene through interference effect.PosttestA. Multiple Choice: Write the letter of the best answer.1. Which part of the human eye regulates the amount of light entering the eye?a. cornea c. lensb. iris d. retina 17

2. An eye forms the image on the retina while a camera forms image in thea. diaphragm c. sensitive filmb. lens d. shutter3. Which statement about the parts of the eye and their uses is true? a. The pupil opens or shuts the eye. b. The eyelid regulates the amount of light. c. The iris enables the eye to see near object. d. The retina serves as the screen where the image is formed.4. The nearsighted person needs a concave lens. This lens can make the image falla. on the eyeball c. before the retina of the eyeb. on the retina of the eye d. beyond the retina of the eye5. Which of the following can be done by a camera but not by the human eye? a. form images of objects b. adjust to dim and bright lights c. change focus from short to long distances d. give a permanent record of the scenes on which it is focused6. Which of the following instruments form a magnified, virtual and erect image?a. camera c. pinhole camerab. human eye d. simple microscope7. A compound microscope is an optical device. Which statement is TRUE about a compound microscope? a. It consists of a single lens. b. It is used to magnify distant object clearly. c. It has an eyepiece that produces a smaller image. d. It is used to view a very small object at very close distance.8. A human eye forms an image which is c. inverted and real a. smaller and erect d. inverted and virtual b. bigger and virtual9. A telescope is an optical device used to c. diminish large object a. view distant object d. diminish small object b. view near object10. Which statement is NOT TRUE about hologram? a. It is a recording of an interference pattern. b. A laser light is needed to make a hologram. c. It forms a true three-dimensional image of the object. d. It is a photographic record of only one view of the object. 18

B. Identify the terms or phrases referred to in the following. ____________ 1. The part of the camera where the image object is formed ____________ 2. The part of the eye which corresponds to the diaphragm of the camera ____________ 3. The kind of lenses used to correct farsightedness ____________ 4. The ability of the eye to adjust the shape of its lens to focus on objects at different positions ____________ 5. An eye defect which focuses the image in front of the retina ____________ 6. A lens prescribed to correct astigmatism ____________ 7. An optical device that forms bigger, erect and virtual image ____________ 8. An optical device that views a small object at close distance ____________ 9. An optical device that views a large object at very far distance ____________ 10. Light used to create a hologram Key to answers on page 21 Key to AnswersPretestA. 6. d B. 6. bifocal lens1. c 7. d 1. retina 7. magnifying glass or2. d 8. b 2. diaphragm3. b 9. b 3. concave lens simple microscope4. c 10. c 4. power of accommodation 8. telescope5. d 5. farsightedness or 9. microscope 10. holography hyperopiaLesson 1Activity 1.1The eyelid, cornea, iris, pupil are the parts of the eye that could be seen.Activity 1.21. The image of the object is formed on the wax paper2. The image observed on the wax paper is smaller, inverted and real. 19

Self-Test 1.1 B. 1. In a camera, the lens is adjusted to A. 1. eyelid form a sharp image while the eyes is 2. iris self-focusing. It has the power of 3. regulates amount of light accommodation to see near and 4. aperture distant objects. 5. lens 2. A camera gives a permanent record 6. refracts light and forms the image of the image while the eye can retain 7. retina an image only at about 1/16 of a second.Lesson 2Self-Test 2.1 1. magnifying glass or simple microscope 2. telescope 3. microscope 4. objective lens 5. eyepieceLesson 3Self-Test 3.1 B. 1. A hologram is a record of an interference pattern while a photograph A. 1. b is a record of an image. 2. c 2. A hologram is capable of reconstructing an exact replica of the 3. c 4. d wavefront of an object 5. True 3. More than one hologram can be recorded in the same area of a photographic plate. 4. In ordinary photography, a lens is used to form an image of an object in photographic film. In holography, no image-forming lens is used. 5. Holography makes use of laser light while in ordinary photography ordinary light is used to form images. 20