Physics Module Form 4 Chapter 5 - Light GCKL What light is? Is a form Light travel in a... and high speed about 300,000 km s -1.

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1 5.1 U N D E R S T A N D I N G R E F L E C T I O N O F L I G H T What light is? Is a form Light travel in a... and high speed about 300,000 km s -1. How the light ray reflected by the surface of mirror? The light ray that strikes the surface of the mirror is called.ray. The light ray that bounces off from the surface of the mirror is called.. 3. The is a line perpendicular to the mirror surface where the reflection occurs. 4. The angle between the incident ray and the normal is called the 5. The angle between the reflected ray and the normal is called. AO = incident ray OB = reflected ray i = angle of incident r = angle of reflected What is the Law of Reflection? Draw the ray diagram of the plane mirror The Laws Of Reflection The incident ray, the reflected ray and the normal..the angle of incident, i, is..to the angle of reflection, r. Consider an object O placed in front of a plane mirror. Measure the distance between the object o and the mirror. 3. Measure the same distance behind the mirror and mark the position as the image. 4. Draw the diverging ray from a point on the image to the corner of the eye. The rays from the image to the mirror must be dotted to show that are virtual. 5. Finally, draw two diverging rays from the object to the mirror to meet the diverging rays from the image. 5-1

2 State the characteristics of the image formed by plane mirror What is meant by virtual image? What is meant by real image? Image that..be seen on a screen. Image that be seen on a screen. Concave mirror CURVED MIRRORS: Convex mirror r f f r State the differences between concave mirror and convex mirror Light (diverged, converged) (virtual,real) principal focus 3.PF = = Distance between the virtual principal focus and the pole of the mirror. Light (diverged, converged) (virtual,real) principal focus 3. PF= = Distance between the real principal focus and the pole of the mirror. Common terminology of reflection of light on a curved mirror Refer to the diagrams above and give the names for the following: Centre of curvature,c =.... Pole of mirror, P =. 3.Radius of curvature,r = CP = 4.Focal length, f = Object distance, =.. 6.Object distance, v =... Construction Rules for Concave Mirror Ray 1 Ray 2 Ray 3 5-2

3 Image formed by concave mirror: A ray parallel to the principle axis is reflected to pass through F. A ray through F is reflected parallel to the principle axis. A ray through C is reflected back along its own path. Using the principles of construction of ray diagram, complete the ray diagrams for each of the cases shown below: u = object distance; v = image distance ; f = focal length ; r = radius of curvature Note: Point of intersection in the position of the image A u < f ( Object between F and P ) Characteristics of image: 3. Application: 3. B u = f ( Object, O is at F ) Characteristics of image: Application: A reflector to produce parallel beam of light such as a reflector in C f < u < 2f or f < u < r ( Object O is between F and C Characteristics of image: 3. I D u = 2f or u = r ( Object,O is at C) Characteristics of image: 3. Application: 5-3

4 Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of image: 2 3. I F u = ( Object,O very far from the lens) Characteristics of image: 3. Application: Construction Rules for Concave Mirror Ray 1 Ray 2 Ray 3 A ray towards F is reflected parallel to the principal axis. A ray parallel to the principal axis is reflected as if it came from F. A ray towards C is reflected back along its own path. Image formed by concave mirror: Using the principles of construction of ray diagram, complete the ray diagrams for each of the cases shown below: u = object distance; v = image distance ; f = focal length ; r = radius of curvature A u < f ( Object between F and P ) Characteristics of image: 3. Application: 5-4

5 Check Yourself: Objective Question: Which of the following is true of the laws of reflection f light? A The angle of incident is equal to the angle of refraction B The incident ray and the reflected ray are always perpendicular to each other. C The incident ray, the reflected ray and the normal line through the point of incidence, all lie on the same plane. 4. A boy stands in front of a plane mirror a distance 5 m. When the boy moves toward the mirror by 2 m, what is the distance between the boy and his new image? A 2m B 4m C 6m D 8 m E 10 m The diagram shows a single ray of light being directed at a plane mirror. 40 What are the angles of incidence and reflection? Angle of incidence Angle of reflection A 40 o 40 o B 40 o 50 o C 50 o 40 o D 50 o 50 o 3. The diagram shows a ray of light from a small bulb strikes a plane mirror. 5. An object is placed in front of a plane mirror. Compare to the object, the image formed in the mirror is always A B C D virtual smaller bigger three times as far away 6. A light ray incident onto a plane mirror at an angle of 50 o The characteristics of an image, formed by a convex mirror for all positions of the object are A diminished, real and inverted B magnified, real, and upright C diminished,virtual and upright D magnified, virtual and inverted 7. A concave mirror has a focal length 20 cm. What happen to the size of image when an object is placed at a distance of 40 cm in front of the mirror? A B C diminished magnified same size of object Where is the image of the bulb formed and its characteristic? A At P and virtual B At Q and real C At R and virtual 5-5

6 8. The figure shows a candle placed in front of a concave mirror of focal length, f. Section A (Paper 2) Structure Question: Diagram 3.1 shows a mirror at the corner of a shop. The image formed is A real, upright and magnified B real, inverted and diminished C virtual, inverted and magnified D virtual, upright and diminished DIAGRAM 3.1 / RAJAH When an object is placed at a point 20 cm in front of a concave mirror, a real image of the same as the object is formed on a screen placed next to the object. What is the focal length of the mirror? A 5 cm B 10 cm C 15 cm D 20 cm 10. Which of the following states the right reason for replacing a plane mirror are used as rear- view mirrors in motor vehicles with a convex mirror? (a) Name the type of mirror shown in Diagram [1 mark] (b) Name one characteristic of the image formed by the mirror... [1 mark] (c) Sketch a ray diagram to show how the image is formed. A To shine the object B To widen the field of view C To produce a brighter image D To produce a sharper image Answer: [3 marks] (d) What is the advantage of using this type of mirror in the shop? [1 mark]

7 Diagram 4.1 shows the image of a patient s teeth seen in a mirror used by a dentist. Section B(Paper 2) Essay Question(20 marks) Diagram 7.1 shows two cars, P and Q, travelling in the opposite directions, passing through a sharp band. A mirror is placed at X. DIAGRAM 4.1 (a) Name the type of the mirror used by the dentist.. [ 1 mark ] (b) State the light phenomenon that causes the image of the teeth.... [ 1 mark ] DIAGAM 7.1 (a) Diagram 7.2 shows an incomplete ray diagram when a plane mirror is placed at X. (c) State two characteristics of the image formed. [ 2 marks ] (d) In the diagram below, the arrow represents the teeth as the object of the mirror. Complete the ray diagram by drawing the required rays to locate the position of the image. DIAGRAM 7.2 (i) Complete the ray diagram in Diagram 7.2 [2 marks] [ 3 marks] 5-7

8 (ii) State the light phenomenon involved in (a)(i). [1 mark] (ii) Complete the ray diagram in Diagram 7.3 [2 marks] (iii) Based on your answer in (a)(i), state the problem experienced by the driver in car P [1 mark] (b) Diagram 7.3 shows an incomplete ray diagram when a curve mirror is placed at X to replace the plane mirror in Diagram 7. The curve mirror is used to overcome the problem that occur in (a)(iii). (iii) Based on your answer in b(ii), how the curve mirror solved the problem in (a) (iii)? [1 mark] (i) DIAGRAM 7.3 Give the name of the curve mirror. [1 mark] ( C) The characteristics of the image formed by the curved mirror in Figure 7.3 is diminished, virtual and upright. (i) What happen to the characteristics of the image when the focal length of the curved mirror is increased?.... [1 mark] (ii) Give the reason for your answer in (c)(i)... [1 mark] 5-8

9 Physics Module Form 4 Chapter 5 - Light GCKL U N D E R S T A N D I N G R E F R A C T I O N O F L I G H T The diagram shows the spoon bent when put inside the water. State the phenomenon occurs. How the phenomenon occurs? Why light is refracted?. Light travel from..medium which is air to.(water), light will be deviated.to the normal. Thus the spoon seems like bending after putting inside the water. It due to change in the of light as it passes from one medium into another. Light travel more in water (or glass) than in air. When a light beam passes from air into glass, one side of the beam is slowed before the other. This makes the beam. Three different cases of refraction Case 1: i = 0,r = 0 Case 2: i > r Case 3: i < r 5-9

10 Physics Module Form 4 Chapter 5 - Light GCKL 2010 When a ray of light crosses the boundry between two different mediums at a right angle or the incident ray..to normal, the ray is but the speed of light is. The angles of incidence and refraction are. Ray is light passes from air(less dense) to glass(denser). ray is bent... the normal the speed of light after entering the glass Ray of light passes from glass(dense) to air(less dense) ray bent..from the normal the speed of light. after emerging from the glass. State the Laws of Refraction The Laws Of Refraction When the light travel from one medium to another medium which has a different optical density: 1. Refractive Index When light travels between two mediums with different optical densities, it changes speed and bends. The speed of light will decrease when it enters an optically denser medium and increases when it enters an optically less dense medium. 3. The angle of bending of light depends on the refractive index of the mediums and the angle of incidence,i. How to define refractive index Refractive index, n is defined as, n = sin i sin r Example: The diagram shows a ray of light passing from air to the block X. where n = Refractive index i = the angle in medium less dense r = the angle in denser medium A material with a higher refractive index has a higher density. The value of refractive index, n 1 The refractive index has no units Calculate the refractive index of the block X. Solution: n = sin 50 sin 40 = 2

11 Physics Module Form 4 Chapter 5 - Light GCKL 2010 Example: n = speed of light in vacuum (air) speed of light in medium The speed of light in vacuum is 3 x 10 8 ms -1 and the speed of light in glass is 2 x 10 8 ms -1. Determine the refractive index of glass. Solution: n = 3 x 10 8 ms -1 2 x 10 8 ms -1 = 5 3.Real Depth and Apparent Depth The refraction of light gives us a false impression of depth. Example: A) The fish in the pond appears to be closer to the surface than it actually is. n = Real depth, H Apparent depth, h The following terms are defined: Real depth,h = The distance of the real O from the surface of the water. (B) The apparent depth a swimming pool looks shallower than it really is. Apparent depth, h= The distance of the..i from the surface of the water. 5-11

12 Physics Module Form 4 Chapter 5 - Light GCKL 2010 ( C) A straight object place in water looks bent at the surface. Explanation: Rays of light from the object travel from Water is a..medium compared to air. 3. Therefore, rays of light.from the normal as they leave the water. The rays of light then enter the eyes of the observer. 4. So the object appears to be the surface of the water. Experiment to investigate the relationship between the angle of incidence and the angle of refraction. Experiment to investigate the relationship between real depth and apparent depth. Hypothesis: The angle of refraction. as the angle of incidence Aim of the experiment : To investigate the relationship between. and.. Variables in the experiment: Manipulated variable:.. Responding variable: Fixed variable:.. List of apparatus and materials: Hypothesis: The apparent depth..as the real depth... Aim of the experiment : To investigate the relationship between.and the.. Variables in the experiment: Manipulated variable:. Responding variable:.. Fixed variable: List of apparatus and materials: Glass block, ray box, white paper protactor, power supply Pin, ruler, water, retort stand,tall beaker

13 Physics Module Form 4 Chapter 5 - Light GCKL 2010 Arrangement of the apparatus: Arrangement of the apparatus: The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable. The glass block is placed on a white paper. The outline of the sides of the glass block are traced on the white paper and labelled as ABCD. The glass block is removed. The normal ON is drawn. By using a protractor, the angle of incidence, i, is measured = 20. The glass block is replaced again on its outline on the paper. A ray of light from the ray box is directed along incidence line. The ray emerging from the side CD is drawn as line PQ. The glass block is removed again. The point O and P is joined and is drawn as line OP. The angle of refraction, r is measured. The experiment is repeated 5 times for the other angles of incidence, i= 30, 40,50, 60 and 70. Tabulate the data: Sin i Sin r Analysis the data: Plot the graph Sin r against Sin i The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable. A pin is placed at the base of the beaker as object O. The another pin is clamped horizontally onto the retort stand as image position indicator, I The beaker is filled with water. By using a ruler,the real depth of the pin is measured, H= 8.0 cm The pin O is seen vertically above the surface of the water. The position of pin I is adjusted until parallax error between the pin O and the pin I is non- existent. By using the ruler again,the position of pin I is measured as the apparent depth = h The experiment is repeated 5 times for the other value of the real depth of water,,i.e. D=10 cm,12 cm,14 cm and 16 cm. Tabulate the data: H/cm h/cm Analysis the data: Plot the graph h against H 5-13

14 Physics Module Form 4 Chapter 5 - Light GCKL 2010 Check Yourself: Objective Question: 1 When light travels from one medium to another, refraction take place. Refraction is caused by the change in the 4 Figure shows a light ray travelling from medium R to medium S. A amplitude of light rays B intensity of light rays C strength of light rays D velocity of light rays 2 An observer cannot see the coin in an empty glass as shown in Figure(a). However, he can see the coin when the glass is filled with water as shown in Figure(b). A B C Which of the following is true? The speed of light in medium R is larger than the speed of light in medium S The optical density of medium R is larger than the optical density of medium S The refractive index of medium R is larger than the refractive index of medium S 5 The diagram shows a light ray directed into a glass block. Which is the angle of refraction? Figure (a) Figure (b) The observer can see the coin in Figure (b) due to A the total internal reflection of light B the refraction of llight C the reflection of light D the diffraction of light 3 Which of the following is not caused by the refraction of light? A A fish in pond appears nearer to the surface of the water B The sunlight reaches to the earth in a curve path C A ruler appears to bend at the water surface. D The sea water appear in blue colour 6 A light ray travels from medium P to medium Q. Which of the following diagrams correctly shows the path of the light? [ Medium P denser medium and Medium Q less dense ] 5-14

15 Physics Module Form 4 Chapter 5 - Light GCKL Which of the following formulae can be used to determine the refractive index of a medium? 7 The diagram shows a light ray travels from liquid L to liquid M. A B C Angle of incidence Angle of refraction Apparent depth Real depth Speed of light in vacuum Speed of light in the medium 10 The diagram shows a light ray travels from the air into medium X. Which of the following diagrams correctly shows the path of the light? [ Refractive index of liquid M > Refractive index of liquid L ] What is the refractive index of medium X? A 0.85 B 24 C 31 D 41 E The diagram shows a light ray travels from the oil into the air. 8 The diagram shows a light ray which travels from the air to the glass. What is the value of k? [ Refractive index of oil = 4 ] What is the refrective index of the glass? A Sin S B Sin P Sin Q Sin R A 44.4o B 45.6o C 54.5o D 55.4o E 58.9o C Sin Q D Sin R Sin R Sin S 5-15

16 Physics Module Form 4 Chapter 5 - Light GCKL The diagram shows a light of ray travels from the air into a glass block. 15 The diagram shows a coin is put at the base of the beaker. The image of the coin appears to be 5 cm from the base of the beaker. What is the refractive index of the glass block? A 38 B 45 C 51 D 62 E The speed of light in the air is 3 x 108 ms-1. What is The speed of light in a plastic block? [ Refractive index of plastic = 2 ] A B C D E 0 x 108 ms-1 5 x 108 ms-1 0 x 108 ms-1 5 x 108 ms x 108 ms-1 14 The diagram shows a boy appearing shorter when he is in a swimming pool. The depth of the water in the pool is 2 m. [ Refractive index of water = 33 ] What is the refractive index of the liquid? A 8 B C 11 D E Answer: What is the apparent depth of the pool? A 0.1 m B 0.3 m C 0.9 m D 1 m E 6 m 5-16

17 Physics Module Form 4 Chapter 5 - Light GCKL 2010 Section A (Paper 2) Structure Question: The Diagram shows a side view of a water-filled aquarium RSTU. An electric lamp, surrounded by a shield with a narrow transparent slit, is immersed in one corner of the aquarium at U. The light ray from the slit shines on the water surface RS at an angle of 40 o as shown in diagram below. R U Water Light ray (a) 40 o DIAGRAM 3.1 What is meant by refractive index of a substance? [1 mark] (b) If the refractive index of water is 33, calculate the critical angle for a ray travelling from water to air. S Aquarium T (C ) (i) Draw a Diagram of the light ray shown on diagram 3.1, meeting the water surface RS, and show its path after meeting the surface. [1 mark] U R Water 40 o Light ray ii. Calculate the angle that this new path makes with RS and label the angle. [2 ma [1 mark] (d) The lamp is then placed outside underneath the aquarium with the light striking to the bottom of the aquarium as shown in Diagram 3. Draw the light ray on Diagram 3.2, after striking the aquarium. [1 mark] S T [ 2 marks] water Lamp Light ray 5-17

18 Physics Module Form 4 Chapter 5 - Light GCKL 2010 An observer is looking at a piece of coin at the bottom of a glass filled with water as shown in Diagram 3. He found that the image of the coin is nearer to the surface of the water. 3. Figure(a) shows an object in a small pond. The depth of the water in the pond is H. The image of the objet appears to be h from water surface. (a)(i) (ii) State a characteristic of image in Diagram 3. [1 mark] Name the science phenomenon involve in the observation above. [1 mark] [ 2 m a r Figure(a) k s ] (a) State the relationship between H and h... (b) When H = 4.5 m and the refractive index of water is 33, [ determine the value of h. 1 1 ] (1 mark) (2 marks) (b) (c) Explain why the image of the coin appears nearer to the surface of the water. [2 marks] On Diagram 3, complete the ray diagram from the coin to the observer's eye. [2 marks] (c) What happen to value of h when the pond is poured with water of refractive index 40? (1 mark) [ 1 ] 5-18

19 Physics Module Form 4 Chapter 5 - Light GCKL 2010 Section B (Paper 2) Essay Question Figure 4(a) shows a pencil placed in a glass of water. Figure 4(b) shows the appearance of print viewed from the top of a thick block of glass placed over it. pencil Glass block ii. Observe Figure 4(a) and Figure 4(b) carefully. Compare the common characteristics of the pencil and the print before and after they are removed from the water and the glass block respectively. Use a physics concept to explain the appearance of the pencil and the print in water and under the glass block respectively. [5 marks] water Figure 4(a) Figure 4(b) (a) i. Why does the pencil appear bent to our eyes? Why does the print appear raised? [1 mark] Answer: 5-19

20 5.3 UNDERSTANDING TOTAL INTERNAL REFLECTION What is meant by total internal reflection? What is meant by critical angle,c? Total internal reflection is the complete reflection of light ray travelling from a to a...medium. Total: because 100% of light is reflected Internal: because it happens inside the glass or denser medium. The critical angle, c, is defined as the angle of incidence (in the denser medium) when the angle of refraction (in the denser medium), r is 90. What are the relationship between the critical angle and total internal reflection? 5-20

21 State the two conditions for total internal reflection to occur When the angle of incidence, i keeps on increasing, r too increases And the refracted ray moves further away from the normal And thus approaches the glass- air boundary. The refracted ray travels along the glass-air boundary. Angle of refraction, r = 90. This is the limit of the light ray that can be refracted in air as the refracted in air cannot be any larger than 90. The angle of incidence in the denser medium at the limit is called the critical angle, c. If the angle of incidence is increased is increased further so that it is greater than the critical angle, (i > c): - no refraction - all the light is totally in the glass This phenomenon is called total internal reflection. What are the relationship between the refractive index, n and critical angle, c? What are the phenomena involving total internal reflection? Mirage In hot days, a person traveling in a car will see an imaginary pool of water appearing on the surface of the road The layes higher up are cooler and denser. Light ray from the sky travels from denser to less dense medium and will refracted away from the normal.

22 The angle of incidence increases until it reach an angle greater than the critical angle. Total internal reflection occurs and the light is reflected towards the aye of the observer. If the observer s eye is in the correct position, he will see a pool of water(image of the sky) appearing on the road surface. This is known as a mirage. Rainbow When sunlight shines on millions of water droplets in the air after rain, a multi coloured arc can be seen. When white light from the sun enters the raindrops, it is refracted and dispersed into its various colour components inside the raindrops. When the dispersed light hit the back of the raindrop, it undergoes total internal reflection. It is then refracted again as it leaves the drop. The colours of a rainbow run from violet along the lower part of the spectrum to red along the upper part. 5-22

23 Give some examples of application of total internal reflection. The sparkling of a diamond A diamond has a high refractive index. The higher the refractive index, the smaller the critical angle. A small critical angle means total internal reflection readily occurs. Light is easily reflected inside the diamond. In this way, more light will be confined within the diamond before refracting out into the air. Periscope The periscope is built using two right angled 45 made of glass. The critical angle of the prism is 42. The angle of incidence is 45 which is greater than the critical angle. Total internal reflection occurs. The characteristics of the image are: Virtual, upright, same size. Give the advantages of the prism periscope compared to mirror periscope. Answer:

24 3. Prism Binocular A light ray experiences two total internal reflections at each prism. So the final image in binoculars is virtual, upright and same size. What are the benefits of using prism in binoculars? 4. Optical Fibres The external wall of a fibre optic is less dense than the internal wall. When light rays travel from a denser internal wall to a less dense external walls at an angle greater than the critical angle, total internal reflection occurs. Give the advantage of using optical fibres cables over copper cables

25 Check Yourself: Objective Question: 1 A ray of red light travelling in glass strikes the glass-air boundary. Some light is reflected and some is refracted. Which diagram shows the paths of the rays? [ Refractive index of medium X = 3 Refractive index of medium Y = 5 ] 4 Which of the following shows total internal reflection? 2 One of the diagram below shows the path of a beam of light that is incident on a water-air surface with angle of incidence greater than the critical angle. Which one is it? 5 The diagram shows light ray XO experiencing total internal reflection when travelling from the glass to air. 3 Which of the following diagram correctly shows the total internal reflection of ray of light? Which statements about total internal reflection are correct? 5-25

26 P - is more than the critical angle of glass Q - The speed of light in the glass is higher than in air R - The refractive index of glass is greater than air A P and Q B P and R C Q and R D P,Q and R 6 The diagram shows a semi-circular plastic block is placed in a liquid. Which of the following is correct? In which direction does the light move from O? A B C D OQ OR OS OT 9 A ray of light incident on one side of a rectangular glass block. If the angle of refraction in the glass block is 40 o, which one of the following diagrams best represents this ray? [ The critical angle of glass is 42 o ] A B C D Density of the plastic block is less than density of the liquid Refractive index of the plastic block is less than refractive index of the liquid Critical angle of the plastic block is less than critical of the liquid Angle of incidence is less than critical angle of the liquid 7 The diagram shows a ray of light passing through medium M to medium N. Which of the following is correct? A The angle of reflection is 55 o B The critical angle of medium M less than 35 o C Density of medium M less than the density of medium N 10 The diagram shows a light ray, P, directed into a glass block. The critical angle of the glass is 42 o. In which direction does the light move from point Q? 8 The figure shows a ray of light PO traveling in a liquid strikes the liquid-air boundary. [ The critical angle of the liquid = 45 o ] 5-26

27 C D the greatest angle of incidence in optically more dense medium the greatest angle of incidence in optically less dense medium 14 Which of the following shows the correct critical angle, c of the semi- circular glass block? 11 The diagram shows a light ray, M, directed into a glass block. The critical angle of the glass is 42 o. In which diagram does the light move from point O? 12 The figure shows a ray of light is incident in air to the surface of Prism A and B. 15 The diagram shows a light ray travelling from air into a plastic block with an angle of incidence,x. What is the critical angle of the plastic? A B C Which comparison is correct? Density of prism A < density of prism B Critical angle of prism A < critical angle of prism B Refractive index of prism A < refractive index of prism B 16 The diagram shows a light ray travelling from air into a glass prism. 13 The critical angle is A B the smallest angle of incidence in optically more dense medium the smallest angle of incidence in optically less dense medium What is the critical angle of the glass? 5-27

28 A 40 o B 50 o C 60 o D 70 o E 80 o 17 The refractive index of water is 33. What is the critical angle of the water. A 44.5 o B 46.9 o C 48.8 o D 49.2 o E 54.3 o 18 The refractive index of plastic block is What is the value of the cosine of the critical angle of the plastic? A 5 B C 13 D E The figure shows a ray of light AO traveling in medium X strikes the medium X-air boundary. [ The refractive index of medium X = 12 ] In which direction does the light move from O? 21 The diagram shows a cross- section of a fibre optic cable. A B C Which comparison is correct? Density of P < density of Q Density of P >density of Q Density of P = density of Q Answer: A OE C OC B OD D OB 20 Which of the following not applies the principle of total internal reflection? A Prism binocular B Mirror periscope C Optical fibre D Road mirage 5-28

29 Section A (Paper 2) Structure Question: Diagram 1 shows a cross-sectional area of an optical fibre which consist of two layers of glass with different refractive index. The glass which forms the inner core, Y is surrounded by another type of glass which forms the outer layer, X. (c) Name other optical device that applies the phenomenon in (a)(i). [ 1 mark ] Figure 4 shows a traveller driving a car on a hot day. The traveller sees a puddle of water on the road a short distance ahead of him. Puddle of water Figure 4 DIAGRAM 1 (a) (i) Name the light phenomenon observed in optical fibre? [ 1 mark ] (ii) Compare the refractive index of outer layer X and inner core Y. [ 1 mark ] (b) The refractive index of inner core Y is 10. Calculate the critical angle of the inner core Y. [ 2 marks ] a) Which part of the air is denser? ( 1 mark ) b) Name a phenomena of light that always depends on the air density when light travels from the sky to the earth before it reaches point X. ( 1 mark ) c) i) What is the phenomenon occurring at point X.. (1 mark ) ii) What is the puddle of water actually? 5-29 ( 1 mark )

30 d) Using the diagram above, explain how the traveller can see the puddle of water on the road. ( 2 marks ) e) Name one optical instrument that uses the phenomenon in (d) ( 1 mark ) 3. Completing the ray diagram below, to show how a periscope works: (critical angle of glass = 42 o ) object Glass Eye 5-30

31 5.4 U N D E R S T A N D I N G L E N S E S Introduction Lenses are made of..material such as glass or clear plastics. They have two faces, of which at least one is Types of lenses (a) lens, also known as converging lens. It.at the centre of the lens. (b) lens, also known as diverging lens. It is.at the centre of the lens. State the differences between convex lens and concave lens Convex lens Concave lens When light ray which are parallel and close to the principle axis.. on a convex lens, they are and... to a point, F on the principle axis. This point is a.. of the convex lens. When light rays are parallel to the principle axis on a concave lens., they are.. and appear to. from the on the principle axis. Common terminology of reflection of light on a curved mirror The focal point, F is a point on the.where all rays are.and..to the axis that to it after passing through a convex lens, or appear to..from it after passing through a concave lens. The focal length, f is the distance between the and the. 3. The optical centre, C is the geometric centre of the lens. It is the point through which light rays pass through without 4. The principle axis is the line passing through the optical centre, C. 5-31

32 Construction rules of convex lens Rule 1: A ray parallel to the principle axis is refracted through the focal point, f. Rule 2: A ray passing through the focal point is refracted parallel to the principle axis. Rule 3: A ray passing through the optical centre, C travels straight without bending. The point of intersection is.. The images formed by a convex lens depend on the object distance, u. Images form by convex lens Using the principles of construction of ray diagram, complete the ray diagrams for each of the cases shown below: u = object distance; v = image distance ; f = focal length Note: Point of intersection in the position of the image A u < f ( Object between F and P ) Characteristics of image: Application: B u = f ( Object, O is at F ) Characteristics of image: Application: 5-32

33 C f < u < 2f or f < u < r ( Object O is between F and C Characteristics of image: Application: D u = 2f or u = r ( Object,O is at C) Characteristics of image: Application: Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of image: 3. Application: 3. F u = ( Object,O very far from the lens) Characteristics of image: 3. Application:

34 Construction rules of concave lens Ray 1: A ray parallel to the principle axis is refracted 1 as if it appears coming from the focal point, F which is located at the same side of the 2 incident ray. 3 Ray 2: A ray passing through the focal point is refracted parallel to the principle axis. Ray 3: A ray passing through the optical centre, C travels straight without bending. The point of intersection is the position of the image. The image formed by a concave lens are always : Image formed by convex mirror: Virtual, upright and diminished. Using the principles of construction of ray diagram, complete the ray diagrams for each of the cases shown below: u = object distance; v = image distance ; f = focal length A u < f ( Object between F and P ) Characteristics of image: 3. Application: (B ) f<u <2f (Object at between f and 2f) Characteristics of image: 3. Application: 5-34

35 Power of lenses Power of a lens = 1. Focal length or P = P = 100 f f( cm) The unit of power of a lens is Dioptre (D) or m -1 Convex lens : the power is taken to be positive Concave lens : the power is taken to be negative f = focal length Linear Magnification (m) : The linear magnification, m define as: Lens Formula Where f = focal length u = object distance v = image distance m = linear magnification h o = object height h i = image height Sign Conventions Type of lenses Convex lens Concave lens Object distance,u Always + Object is always placed to the left of the lens Always + Object is always placed to the left of the lens Image distance, v + if the image is real ( image is formed on the right side of the lens. - if the image is virtual ( image is formed on the left side of the lens). + if the image is real ( image is formed on the right side of the lens - if the image is virtual ( image is formed on the left side of the lens). Focal length, f Always + Always - Power of length, P Always + Always - Linear magnification, m I m I = 1 Size of image Image and object are the same size I m I > 1 I m I < 1 Enlarged image Diminished image 5-35

36 Meaning of real image and virtual image A real imge is one which can be cast on a screen. A virtual imge is one which cannot be cast on a screen. Check Yourself: Objective Question: 1 The image produced by a lens is caused by the A total internal reflaction of ray B diffraction of ray C refraction of ray D reflection of ray 2 The diagram shows parallel rays of light is incident to a combination of plastics with different refractive index. 4 Which of the following drawing is not correct path of the light rays? Which of the following diagrams is correct? 3 The diagram shows parallel rays of light passing through a liquid in glass container. [ The refractive index of the liquid = 35 ] 5 Which of the following is true? A The unit of the power of lens is Watt B The power of a convex lens is negative C A lens with a shorter focal length has a lower power D The rays of light passes through the optical centre of lens without any refraction Which of the following diagrams is true? 5-36

37 6 Diagram shows light rays passing through a convex lens. 10 Figure shows four light rays A,B,C and D passing through a convex lens. F is the focal point of the length. Which of the following path of the light rays is not correct? What is the distance P? A Image distance B Object distance C Focal length D Optical length 7 The diagram shows the action of a magnifying glass. Which point is the principal focus of the lens? 11 What is the power of a convex lens which has a focal length 50 cm? A -0.2 D B 0.2 D C -0 D D 0 D E 4.0 D 12 The power of a lens is - 40 D. What is the type of the lens and its focal length? 8 The diagram shows an image,i is formed by a convex lens. Where is the position of the object? Type of length Focal length A Concave lens -5 x 10 2 m B Concave lens -5 x 10-2 m C Convex lens -5 x 10 2 m D Convex lens -5 x 10-2 m E Concave lens -4.0 x 10-2 m 13 A convex lens of focal length,f. The lens produces a enlarged, virtual and upright image.the object distance is 9 The diagram shows an image,i is formed by a concave lens. Where is the position of the object? A B C D less than f between f and 2f same as 2f more than 2f 14 A light bulb is placed at the principal focus of a convex lens. After travelling through the lens the rays of light is A parallel B converge C diverge 5-37

38 15 The focal length of a convex lens is f. Which of the following object distances, u will produced an inverted image? A u < f B u >f C f < u < 2f D u > 2f 16 The diagram shows an object which is placed at u cm from centre of a convex lens. The focal length of the lens is 20 cm. 19 A convex lens of focal length 20.0 cm is turned to face a distant object. The position of the screen is adjusted until a sharp inverted image is formed on the screen. What is the distance of the screen from the lens? A 15.0 cm B 20.0 cm C 25.0 cm D 40.0 cm E 50.0 cm 20 The characteristics image is produced by a concave lens is Which of the following characteristics of the image is not correct when u is 10 cm,15 cm, 35 cm and 45 cm from the lens? u / cm Characteristics of the image A 10 B 15 C 35 D 45 Virtual and bigger Virtual and bigger Real and smaller Real and smaller 17 An object is placed 25 cm in front of a convex lens and its image is formed at infinity. If the object is placed 20 cm in front of the lens, the image is A inverted B smaller than object C formed on the same side as the object 18 The diagram shows an object,o is placed in front of a convex lens produced an image, I. A B C D magnified,virtual,upright diminished,virtual,upright magnified,real,inverted diminished,real,inverted 21 An object is placed at 18.0 cm from a convex lens of focal length 20.0 cm. What is the the characteristics of image? A B C D virtual, upright and magnified real, inverted and magnified virtual,upright and diminished real, inverted and diminished 22 A lens is placed between a light bulb and a secreen. The distance between the light bulb and screen is 60.0 cm. The position of the lens is adjusted until the size of the image is same as the size of the object. What is the type and the focal lenghth of the lens? Type of lens Focal length A Convex lens 30 cm B Convex lens 15 cm C Concave lens 30 cm D Concave lens 15 cm Which of the following is not true? A The focal length of the lens is 60 cm B The linear magnification is 1 C The image I is a real image 5-38

39 23 An object is placed at a distance 10 cm in front of a convex lens of power 5D. What is the image distance and the characteristic of the image? Image distance A 10.0 cm B 10.0 cm C 20.0 cm D 20.0 cm Characteristic of the image Virtual image Real image Virtual image Real image 24 An object is placed at a distance 80 cm in front of a concave lens of focal length 20 cm. What is the image distance and the characteristic of the image? Image distance Characteristic of the image A 16.0 cm B 16.0 cm C 26.7 cm D 26.7 cm same side of the lens as the object the other side of the lens as the object same side of the lens as the object the other side of the lens as the object 25 The diagram shows an image I of an object O is formed by a convex lens. What is the linear magnification of the image? A 0.5 B 0 C 3.0 D 4.0 E An object is placed at a distance30 cm from a convex lens with a focal length of 25.0 cm. What is the linear magnification? A 2 B 3 C 4 D 5 E A convex lens with a focal length of 20.0 cm to form an image which is 2 times the size of the object. What is the object distance? A 10.0 cm B 15.0 cm C 30.0 cm D 40.0 cm E 60.0 cm 28 An object of height 5 cm is placed at 15 cm from a convex lens of focal length 10.0 cm. What is the image height? A 5 cm B 10 cm C 15 cm D 20 cm E 25 cm 29 An object of height 6.0 cm is placed at 8 cm from a convex lens of power 50 D. What is the image height? A 2 cm B 4 cm C 5 cm D 6 cm E 8 cm 30 A convex lens is used to produce a real, magnified and inverted image. What is the effect on the image produced when the upper portion of the lens is covered by a coin? A B C The upright image is formed The size of the image is reduced The brightness of the image is reduced 31 The diagram shows a graph of object distance,u against image distance,v of the lens. What is the focal length of the lens? A 5 cm B 10 cm C 20 cm D 40 cm E 80 cm

40 32 The diagram shows a graph of image distance,v against linear magnification,m of the lens. (a) State the light phenomenon that causes the image FIZIK to be enlarged. (1 mark) (b) What is the change size of the image if the water is replaced with a transparent liquid of a greater density? What is the focal length of the lens? A 14.0 cm B 15.0 cm C 16.0 cm D 17.0 cm E 18.0 cm Answer: (1 mark) (c) The glass of water is replaced with a lens M with focal length of 10 cm. The distance between the book cover and the centre of the lens is 8 cm. It is observed that the image FIZIK is enlarged. (i) Name the type of lens M. (1 mark) (ii) Calculate the distance of the image from lens M. Section A (Paper 2) Structure Question: 1 The Figure shows an image of letters FIZI when viewed through a glass of water. 2 The diagram shows an object is placed in front of a convex of focal length 15.0 cm (a) (i) Complete the ray diagram in the diagram above to show the formation of the final image (3 marks)

41 (ii) State the characteristics of the image. (b) If the object is now placed in front of the lens, an image which is 4 times the size of the object is formed.... (2 marks) (b) Determine the linear magnification (i) Calculate the object distance. (2 marks) (2 marks) (c) The object height is 5 cm,calculate the image height. (2 marks) (d) What will happen to the characteristis of the image when (i) the convex lens is replaced by a concave lens of focal length 15.0 cm.... (2 marks) (ii) State the characteristics of the image. (2 marks)... (c) State the light phenomenon that causes the image is formed by the lens? ( 1 mark)... (d) What is the effect on the image produced when the lower portion of the lens is covered by a card? (1 mark)... (ii) the object is placed at the 10 cm mark.... (2 marks) 3 When an object is placed 40 cm from a convex lens,the image formed is of the same size as the object. (a) Determine, (i) the focal length of the lens (1 mark) (ii) the power of the lens (1 mark) 5-41

42 5.5 T H E U S E S O F L E N S E S I N O P T I C A L D E V I C E S Introduction There are many types of optical devices used lenses such as magnifying glass, microscope, telescope, camera and slide projector etc. For every types of the devices we must learn about the uses of the instruments, lens characteristics is used, normal adjustment of the instruments, ray diagrams and the characteristics of the final image which are formed. Compound Microscope Give the use of a compound microscope. A microscope is used to observe and magnify tiny objects such as bacteria. Draw a diagram to describe the formation of image formed by microscope. It consist of two powerful.lenses of short focal length (5.0 cm-10.0 cm) The lens which receives light rays from the objects is called the lens. The lens which is used for viewing the final image is called the.. lens. 3. The focal length of the objective lens is f o whereas the focal length of the eyepiece lens is f e. 4. The object is placed at a distance between..so that the imaged formed is.., and.in front of the eyepiece lens. 5. The position of the eyepiece lens is adjusted until the position of the first image is less than f o from the eyepiece lens. Define the characteristics of the image formed by objective lens o microscope. The final image formed,..and 5-42

43 Magnifying glass Give the use of a compound microscope. A microscope is used to observe and magnify tiny objects such as bacteria. Draw a diagram to describe the formation of image formed by microscope. It consists of two powerful lenses of..focal lengths. An object is placed at a position..the focal length of the lens. 3. The magnifying power if the focal length of the lens is shorter. 4. A shaper and larger image is seen at the near point of the eye. In general, the near point is taken as 25 cm. Define the characteristics of the image formed by objective lens o microscope. The image formed is,..and Astronomical Telescope Give the use of a compound microscope. A microscope is used to observe and magnify tiny objects such as bacteria. Draw a diagram to describe the formation of image formed by microscope. 5-43

44 It consist of an..lens and.lens. The objective lens is used to receive light rays from distant object. 3. The first image formed is at focal point of the objective lens F o. It is, and. 4. The first image now becomes the object for the eyepiece lens. 5. The lens is adjusted so that the first image is situated at the focal point of the eyepiece lens, F e. 6. The telescope is said to be in normal adjustment. 7. For normal adjustment of the telescope, the separation between the two lenses is f o + f e. Define the characteristics of the image formed by objective lens o microscope. The first image formed is at focal point of the objective lens F o.it is,. and... The final image formed is at 4. Slide Projector What is the function of each component of a slide projector? Slide Projector Lens Condenser Lens Component Acts as an object Functions The lens has to be placed far away from the screen in order to get a large image. Acts as a heat filter to protect slide from getting over heated. Draw a diagram to describe the formation of image formed by microscope. It uses a lens to form a.,. and image of the slide or film on a screen. The slide being the is placed between... from the projector lens The lamp is placed at the focal point of the mirror to reflect all light from the lamp back to the.. 3. The movable projector lens focuses a sharp, and... image onto a screen. 4. The slide should be placed upside-down(inverted) in order to form an image on the screen. 5-44

45 Define the characteristics of the image formed by objective lens of microscope. Upright, real, magnified 5. Camera Draw a diagram to describe the formation of image formed by microscope. State the parts in a camera and their functions? The lens is used to produce a, and. image on a light sensitive film at the camera. The is used to adjust the size of the exposure time when taking photographs. 3. The..speed is used to control the exposure time when taking photographs. Check Yourself: Objective Question: 1 Which of the following combinations is the characteristics of a magnifying lens? Object distance/cm Focal length/ cm A 5 10 B 8 5 C 10 5 D A convex lens is used as a magnifying glass. What are the characteristics of the image? A magnified,upright,virtual B magnified,upright,real C magnified,inverted,virtual D magnified,inverted,real 3 Which of the following is true about the eyepiece of a microscope? A B C D Consist of a concave lens which has lower power than the objective lens. Consist of a convex lens which has lower power than the objective lens. Consist of a concave lens which has higher power than the objective lens. Consist of a convex lens which has higher power than the objective lens. 5-45

46 4 Which of the following is true concerning the operation of a compound microscope? A B C The focal length of objective lens greater than the focal length of eyepiece Both objective lens and eyepiece has a high power. The characteristics of final image are magnified, upright and virtual 5 The characteristics of image is formed by the objective lens of a microscope are A virtual,diminished,upright B real,magnified,inverted C virtual,magnified,inverted D real,magnified,upright 6 Which of the following statements about the objective lens and eyepiece of a telescope? Power of objective lens Power of eyepiece A low high B high low C low low D high high 7 Two convex lens of power 5D and 20 D respectively is used in a telescope. What is the distance between the lens in normal adjustment? A 8.0 cm B 17.5 cm C 25 cm D 45.0 cm E 50.0 cm 8 Two convex lens of focal length 100 cm and 5 cm respectively is used in a telescope. What is the linear magnification of the telescope? 9 A telescope has two convex lens of power 4.0 D and 20.0D respectively. Which of the following is true? Linear magnification Distance between the lens /cm A B C D E The characteristics of final image in a telescope are A virtual,upright,magnified,located at the focal point B real,inverted,magnified,located at infiniti C virtual,inverted,magnified,located at infiniti 11 The characteristics of the image is formed by a camera are A B C D virtual,upright,enlarged real,inverted,diminished virtual,inverted,diminished real,upright,enlarged 12 The image is formed by a slide projector is A enlarged,real,upright B enlarged,real,inverted C diminished,virtual,upright D diminished,real,inverted 13 Which of the following optical instrument produced real image? A 0.05 B 20 C 100 D 105 E 500 A Telescope C Microscope B Magnifying glass D Slide projector 5-46

47 Answer: (c) State two differences between telescope and microscope by completing the table below. Telescope Microscope Section A (Paper 2) Structure Question: 1 The diagram shows the arrangement of the lenses in a compound microscope. 2 The diagram shows the arrangement of the lenses in a telescope. The power of lens A and lens B are 0.5 D and 5D respectively. (a) Complete the ray diagram in the diagram above. Answer: (a) Why do the light rays PQ and RS are parallel? (1 mark). (b) State the focal length of (i) lens A (2 marks)... (ii) lens B (2 marks) (b) State the characteristics of the final image formed. (1 mark)... (c) What is the distance between lens A and lens B? (2marks)