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### 5.0 light

1. 1. Physics Module Form 4 Chapter 5 - Light GCKL 2011 5.1 UNDERSTANDING REFLECTION OF LIGHTWhat light is? Is a form ……………Light travel in a .................. and high speed about 300,000 km s-1.How the light 1. The light ray that strikes the surface ofray reflected the mirror is called ……………….ray.by the surface 2. The light ray that bounces off from theof mirror? 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 AO = incident ray the normal is called the ……………… OB = reflected ray 5. The angle between the reflected ray and i = angle of incident the normal is called r = angle of reflected …………………………………………….What is the The Laws Of ReflectionLaw of 1. The incident ray, the reflected ray and the normal …………………………………..TheReflection ? angle of incident, i, is ………………..to the angle of reflection, r.Draw the raydiagram of the 1. Consider an object O placed in front of aplane mirror plane mirror. 2. 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. 2. Physics Module Form 4 Chapter 5 - Light GCKL 2011State the 1.characteristics 2.of the image 3.formed by 4.plane mirror 5.What is meantby virtualimage? Image that ……………..be seen on a screen.What is meantby real image? Image that ………………be seen on a screen. CURVED MIRRORS: Concave mirror Convex mirror f f r rState the 1.Light (diverged, converged) 1.Light (diverged, converged)differences 2.(virtual,real) principal focus 2. (virtual,real) principal focusbetween 3.PF = …………………………… 3. PF= ………………………………concave mirror = Distance between the virtual = Distance between the real principal focusand convex principal focus and the pole of the and the pole of the mirror.mirror mirror.Common Refer to the diagrams above and give the names for the following:terminology ofreflection of 1.Centre of curvature ,C = ……………………………………………………………………………….light on a ...........................................................................................................curved mirror 2.Pole of mirror, P = ………………………………………………………………………. 3.Radius of curvature ,r = CP = …………………………………………………………… 4.Focal length, f = …………………………………………………………………………. ................................................................................................................ 5.Object distance, = ……………………………………………………………………….. 6.Object distance , v = ..........................................................................................................ConstructionRules forConcaveMirror Ray 1 Ray 2 Ray 3 5-2
3. 3. Physics Module Form 4 Chapter 5 - Light GCKL 2011 A ray parallel to the A ray through F is reflected A ray through C is reflected principle axis is reflected to parallel to the principle back along its own path. pass through F. axis.Image formed Using the principles of construction of ray diagram, complete the ray diagrams for each of theby concave cases shown below:mirror: 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 Application: image: 1. 1. 2. 2. 3. 3. B u = f ( Object, O is at F ) Characteristics of Application: image: A reflector to 1. produce parallel beam of light such as a reflector in 1. 2. C f < u < 2f or f < u < r ( Object O is Characteristics of between F and C image: 1. 2. 3. I D u = 2f or u = r ( Object ,O is at C) Characteristics of Application: image: 1. 1. 2. 3. 5-3
4. 4. Physics Module Form 4 Chapter 5 - Light GCKL 2011 Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of image: 1. 2 3. I F u =  ( Object ,O very far from the lens) Characteristics of Application: image: 1. 2. 3.ConstructionRules forConcaveMirror Ray 1 Ray 2 Ray 3 A ray parallel to the A ray towards F is reflected A ray towards C is reflected principal axis is reflected as parallel to the principal back along its own path. if it came from F. axis.Image formed Using the principles of construction of ray diagram, complete the ray diagrams for each of theby concave cases shown below:mirror: u = object distance; v = image distance ; f = focal length ; r = radius of curvature A u < f ( Object between F and P ) Characteristics of Application: image: 1. 1. 2. 2. 3. 5-4
5. 5. Physics Module Form 4 Chapter 5 - Light GCKL 2011Check Yourself:Objective Question:1. Which of the following is true of the laws of reflection f light? 4. A boy stands in front of a plane mirror a distance A The angle of incident is equal to the angle of 5 m . When the boy moves toward the mirror by 2 refraction m , what is the distance between the boy and his B The incident ray and the reflected ray are new image? always perpendicular to each other. C The incident ray , the reflected ray and the A 2m B 4m normal line through the point of incidence, all C 6m D 8m lie on the same plane. E 10 m2. The diagram shows a single ray of light being 5. An object is placed in front of a plane mirror. directed at a plane mirror. Compare to the object, the image formed in the mirror is always A virtual 40° B smaller C bigger D three times as far away What are the angles of incidence and reflection? Angle of incidence Angle of reflection A 40o 40o 6. A light ray incident onto a plane mirror at an B 40o 50o angle of 50o C 50o 40o The characteristics of an image , formed by a D 50o 50o convex mirror for all positions of the object are A diminished, real and inverted B magnified , real, and upright C diminished ,virtual and upright3. The diagram shows a ray of light from a small bulb D magnified , virtual and inverted strikes a plane mirror. 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 diminished B magnified C 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. 6. Physics Module Form 4 Chapter 5 - Light GCKL 20118. The figure shows a candle placed in front of a Section A (Paper 2) concave mirror of focal length, f. Structure Question: 1. 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 DIAGRAM 3.1 / RAJAH 3.1 D virtual, upright and diminished9. When an object is placed at a point 20 cm in (a) Name the type of mirror shown in Diagram 3.1 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 [1 mark] mirror? (b) Name one characteristic of the image formed A 5 cm by the mirror. B 10 cm C 15 cm …………………………………………………….. D 20 cm [1 mark] (c) Sketch a ray diagram to show how the image10. Which of the following states the right reason for is formed. replacing a plane mirror are used as rear- view mirrors in motor vehicles with a convex mirror ? A To shine the object B To widen the field of view C To produce a brighter image D To produce a sharper imageAnswer: 1 2 3 4 5 [3 marks] 6 (d) What is the advantage of using this type of 7 mirror in the shop? 8 9 …………………………………………………………… 10 [1 mark] 5-6
7. 7. Physics Module Form 4 Chapter 5 - Light GCKL 20112. Diagram 4.1 shows the image of a patient’s teeth Section B(Paper 2) seen in a mirror used by a dentist. 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 ] DIAGAM 7.1 (b) State the light phenomenon that causes the image of the teeth. (a) Diagram 7.2 shows an incomplete ray diagram when a plane mirror is placed at X. ………………………………………………... [ 1 mark ] (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. DIAGRAM 7.2 Complete the ray diagram by drawing the (i) Complete the ray diagram in Diagram 7.2 required rays to locate the position of the image. [2 marks] [ 3 marks] 5-7
8. 8. Physics Module Form 4 Chapter 5 - Light GCKL 2011(ii) State the light phenomenon involved in (a)(i). (ii) Complete the ray diagram in Diagram 7.3 [2 marks] ………………………………………………… [1 mark](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 7.2. 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] ( 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 DIAGRAM 7.3 image when the focal length of the curved mirror is increased? (i) Give the name of the curve mirror. ……………………………………………………….. …………………………………[1 mark] ……………………………………………….. [1 mark] (ii) Give the reason for your answer in (c)(i). …………………………………………………….. ………………………………………………… [1 mark] 5-8
9. 9. Physics Module Form 4 Chapter 5 - Light GCKL 2010 5.2 UNDERSTANDING REFRACTION OF LIGHT The diagram shows the spoon bent when put inside the water.State thephenomenon ………………………………….occurs.How the Light travel from ………………..medium which is air to …………………….(water), light willphenomenon be deviated ………………….to the normal. Thus the spoon seems like bending after puttingoccurs? inside the water.Why light is It due to change in the …………………of light as it passes from one medium into another.refracted? 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 differentcases of refraction Case 1: Case 2: Case 3: i = 0 ,r = 0 i>r i<r 5-9
10. 10. Physics Module Form 4 Chapter 5 - Light GCKL 2010 When a ray of light crosses Ray is light passes from Ray of light passes from the boundry between two air(less dense) to glass(dense) to air(less different mediums at a right glass(denser). dense) angle or the incident ray ………………..to normal,  ray is bent  ray bent  the ray is ……………………... ………………..from …………………but the normal the normal the speed of light is …………………….  the speed of light  the speed of light The angles of …………………after ……………………. incidence and entering the glass after emerging from refraction the glass. are………………….State the Laws of The Laws Of RefractionRefraction When the light travel from one medium to another medium which has a different optical density: 1…………………………………………………………………………………………………… 2. ………………………………………………………………………………………………….Refractive Index 1. When light travels between two mediums with different optical densities, it changes speed and bends. 2. 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 1. Refractive index, n is defined as, Example:refractive index n = sin i The diagram shows a ray of light passing from sin r 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 Calculate the refractive index of the block X.  The refractive index has no units. Solution: n = sin 50° sin 40° = 1.2 5-10
11. 11. Physics Module Form 4 Chapter 5 - Light GCKL 2010 2. Example: n = speed of light in vacuum (air) The speed of light in vacuum is 3 x 108 ms-1 speed of light in medium and the speed of light in glass is 2 x 108 ms-1 . Determine the refractive index of glass. Solution: 0r n = va n = 3 x 108 ms-1 2 x 108 ms-1 vm = 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: Or (B) The apparent depth – a swimming pool Real depth,H = The distance of the real looks shallower than it really is. n=H ……………… O from the surface of the water. h Apparent depth, h= The distance of the ………………..I from the surface of the water. 5-11
12. 12. Physics Module Form 4 Chapter 5 - Light GCKL 2010 ( C) A straight object place in water looks bent at the surface. Explanation: 1.Rays of light from the object travel from ……………………… 2.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 Experiment to investigate the relationship betweenangle of incidence and the angle of refraction. real depth and apparent depth.Hypothesis: Hypothesis:The angle of refraction ………………. as the angle of The apparent depth …………………..as the real depthincidence ……………………… ……………………….. .Aim of the experiment : Aim of the experiment :To investigate the relationship between…………………………. and …………………….. To investigate the relationship between ……………….and the …………………………………..Variables in the experiment: Variables in the experiment:Manipulated variable: …………………………….. Manipulated variable: …………………….Responding variable: ……………………………… Responding variable: ……………………..Fixed variable: …………………………………….. Fixed variable: ………………………………List of apparatus and materials: List of apparatus and materials:Glass block, ray box, white paper protactor, power Pin, ruler, water, retort stand ,tall beakersupply . 5-12
13. 13. Physics Module Form 4 Chapter 5 - Light GCKL 2010Arrangement of the apparatus: Arrangement of the apparatus:The procedure of the experiment which include themethod of controlling the manipulated variable and The procedure of the experiment which include thethe method of measuring the responding variable. 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 A pin is placed at the base of the beaker as object O.the white paper and labelled as ABCD. The another pin is clamped horizontally onto the retortThe glass block is removed. stand as image position indicator, IThe normal ON is drawn. The beaker is filled with water.By using a protractor , the angle of incidence, i , is By using a ruler ,the real depth of the pin is measured, H=measured = 20°. 8.0 cmThe glass block is replaced again on its outline on the The pin O is seen vertically above the surface of thepaper. water.A ray of light from the ray box is directed along The position of pin I is adjusted until parallax errorincidence line. between the pin O and the pin I is non- existent.The ray emerging from the side CD is drawn as line PQ. By using the ruler again ,the position of pin I is measuredThe glass block is removed again. as the apparent depth = hThe point O and P is joined and is drawn as line OP. The experiment is repeated 5 times for the other value ofThe angle of refraction, r is measured. the real depth of water, ,i.e. D=10 cm,12 cm,14 cm andThe experiment is repeated 5 times for the other angles of 16 cm.incidence, i= 30° , 40°,50°, 60° and 70°. Tabulate the data: H/cmTabulate the data: Sin i h/cm Sin r Analysis the data:Analysis the data:Plot the graph Sin r against Sin i Plot the graph h against H 5-13
14. 14. Physics Module Form 4 Chapter 5 - Light GCKL 2010Check Yourself:Objective Question:1 When light travels from one medium to another, 4 Figure shows a light ray travelling from medium refraction take place. Refraction is caused by the R to medium S. change in the A amplitude of light rays B intensity of light rays C strength of light rays D velocity of light rays Which of the following is true?2 An observer cannot see the coin in an empty glass as shown in Figure(a). However , he can see the A The speed of light in medium R is larger than coin when the glass is filled with water as shown the speed of light in medium S in Figure(b). B The optical density of medium R is larger than the optical density of medium S C 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 light3 Which of the following is not caused by the refraction of light ? 6 A light ray travels from medium P to medium Q. A A fish in pond appears nearer to the surface Which of the following diagrams correctly shows of the water the path of the light ? B The sunlight reaches to the earth in a curve [ Medium P denser medium and Medium Q less path dense ] C A ruler appears to bend at the water surface. D The sea water appear in blue colour 5-14
15. 15. Physics Module Form 4 Chapter 5 - Light GCKL 2010 9 Which of the following formulae can be used to determine the refractive index of a medium? A Angle of incidence Angle of refraction B Apparent depth Real depth C Speed of light in vacuum Speed of light in the medium7 The diagram shows a light ray travels from liquid L to liquid M. 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 1.24 C 1.31 D 1.41 E 1.58 11 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 = 1.4 ] A 44.4o B 45.6o What is the refrective index of the glass? C 54.5o A Sin S B Sin P D 55.4o Sin Q Sin R E 58.9o C Sin Q D Sin R Sin R Sin S 5-15
16. 16. Physics Module Form 4 Chapter 5 - Light GCKL 201012 The diagram shows a light of ray travels from the 15 The diagram shows a coin is put at the base of air into a glass block. 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 1.38 What is the refractive index of the liquid? B 1.45 A 8 B 5 C 1.51 13 8 D 1.62 C 11 D 13 E 1.74 5 8 E 19 1413 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 = 1.2 ] A 1.0 x 108 ms-1 B 1.5 x 108 ms-1 Answer: C 2.0 x 108 ms-1 D 2.5 x 108 ms-1 1 11 E 3.0 x 108 ms-1 2 12 3 1314 The diagram shows a boy appearing shorter when 4 14 he is in a swimming pool. The depth of the water 5 15 in the pool is 1.2 m. 6 16 [ Refractive index of water = 1.33 ] 7 17 8 18 9 19 10 20 What is the apparent depth of the pool? A 0.1 m B 0.3 m C 0.9 m D 1.1 m E 1.6 m 5-16
17. 17. Physics Module Form 4 Chapter 5 - Light GCKL 2010Section A(Paper 2)Structure Question: (C ) (i) Draw a Diagram of the light ray shown on1. The Diagram shows a side view of a water-filled diagram 3.1, meeting the water surface RS, and showaquarium RSTU. An electric lamp, surrounded by a its path after meeting the surface. [1 mark]shield with a narrow transparent slit, is immersed inone corner of the aquarium at U. The light ray fromthe slit shines on the water surface RS at an angle of40o as shown in diagram below. R S Water 40oR S o Water 40 Aquarium Light ray Light ray U T U T DIAGRAM 3.1 ii. Calculate the angle that this new path makes with RS and label the angle. ma [2 [1 mark] (a) What is meant by refractive index of a substance? (d) The lamp is then placed outside underneath [1 mark] the aquarium with the light striking to the bottom of the aquarium as shown in Diagram 3.2. Draw the light ray on Diagram 3.2, after striking the aquarium. (b) If the refractive index of water is 1.33, calculate the critical angle for a ray travelling [1 mark] from water to air. [ 2 marks] water Light ray Lamp 5-17
18. 18. Physics Module Form 4 Chapter 5 - Light GCKL 20102. An observer is looking at a piece of coin at the 3. Figure(a) shows an object in a small pond. The bottom of a glass filled with water as shown in depth of the water in the pond is H. The image of Diagram 3. He found that the image of the coin is nearer to the surface of the water. the objet appears to be h from water surface. [ 2 m a r Figure(a) k s ] (a) State the relationship between H and h .................................................................... (a)(i) State a characteristic of image in Diagram 3. (1 mark) (b) When H = 4.5 m and the refractive index of [1 mark] water is 1.33,[ determine the value of h . 1 (2 marks) 1 ] (ii) Name the science phenomenon involve in the observation above. [1 mark] (b) Explain why the image of the coin appears nearer to the surface of the (c) What happen to value of h when the pond is water. poured with water of refractive index 1.40 ? [2 marks] …………………………………………… (c) On Diagram 3, complete the ray diagram from the coin to the observers (1 mark) eye. [2 marks] [ 1 ] 5-18
19. 19. Physics Module Form 4 Chapter 5 - Light GCKL 2010Section B (Paper 2)Essay Question ii. Observe Figure 4(a) and Figure 4(b) carefully.1. Figure 4(a) shows a pencil placed in a glass of Compare the common characteristics of the pencilwater. Figure 4(b) shows the appearance of print and the print before and after they are removedviewed from the top of a thick block of glass placed from the water and the glass block respectively.over it. Use a physics concept to explain the appearance pencil Glass block 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. 20. Physics Module Form 4 Chapter 5 - Light GCKL 2011 5.3 UNDERSTANDING TOTAL INTERNAL REFLECTIONWhat is meant by Total internal reflection is the complete reflection of light ray travelling from a …………………total internal to a .................................medium.reflection? Total: because 100% of light is reflected Internal: because it happens inside the glass or denser medium.What is meant by The critical angle, c, is defined as the angle of incidence (in the denser medium) when the anglecritical angle ,c? of refraction (in the denser medium), r is 90°.What are therelationshipbetween thecritical angle andtotal internalreflection ? 5-20
21. 21. Physics Module Form 4 Chapter 5 - Light GCKL 2011  When the angle of  The refracted ray  If the angle of incidence, i keeps on travels along the incidence is increasing, r too glass-air boundary. increased is increases  Angle of refraction, r increased further so = 90°. that it is greater than  And the refracted ray moves further away  This is the limit of the critical angle, the light ray that can (i > c): from the normal be refracted in air as - no refraction  And thus approaches the refracted in air - all the light is the glass- air cannot be any larger totally in the boundary. than 90°. glass  The angle of  This phenomenon is incidence in the called total internal denser medium at the reflection. limit is called the critical angle, c.State the twoconditions for 1.total internalreflection to occur 2.What are therelationshipbetween therefractive index, nand critical angle,c?What are the 1. Mirage  In hot days, a person traveling in aphenomena car will see an imaginary pool ofinvolving total water appearing on the surface ofinternal reflection? 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. 5-21
22. 22. Physics Module Form 4 Chapter 5 - Light GCKL 2011  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. 2. 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. 23. Physics Module Form 4 Chapter 5 - Light GCKL 2011Give some 1. The sparkling of a diamond  A diamond has a high refractiveexamples of index.application of totalinternal reflection.  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. 2. 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: 1. ……………………………………………… ……………………………………………… ……………………………………………… ………………………………………….. 2. ……………………………………………… ……………………………………………… ……………………………………………… …………………………………………… 5-23
24. 24. Physics Module Form 4 Chapter 5 - Light GCKL 2011 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? 1. ……………………………………………… ……………………………………………… ……………………………………………… 2. ……………………………………………… ……………………………………………… ……………………………………………… 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. 1. ................................................................. 2. ................................................................. ................................................................. 3. ................................................................. ................................................................. 5-24
25. 25. Physics Module Form 4 Chapter 5 - Light GCKL 2011 4. ................................................................. .................................................................Check Yourself:Objective Question:1 A ray of red light travelling in glass strikes the [ Refractive index of medium X = 1.3 glass-air boundary . Some light is reflected and Refractive index of medium Y = 1.5 ] some is refracted. Which diagram shows the paths of the rays? 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. Which statements about total internal reflection3 Which of the following diagram correctly shows are correct? the total internal reflection of ray of light? 5-25
26. 26. Physics Module Form 4 Chapter 5 - Light GCKL 2011 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 In which direction does the light move from O ? C Q and R D P,Q and R A OQ B OR6 The diagram shows a semi-circular plastic block C OS is placed in a liquid. D 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 40o , which one of the following diagrams best represents this ray? [ The critical angle of glass is 42o ] Which of the following is correct? A Density of the plastic block is less than density of the liquid B Refractive index of the plastic block is less than refractive index of the liquid C Critical angle of the plastic block is less than critical of the liquid D Angle of incidence is less than critical angle of the liquid7 The diagram shows a ray of light passing through medium M to medium N. Which of the following is correct? 10 The diagram shows a light ray, P, directed into a glass block. The critical angle of the glass is 42o. A The angle of reflection is 55o In which direction does the light move from point B The critical angle of medium M less than 35o Q? C Density of medium M less than the density of medium N8 The figure shows a ray of light PO traveling in a liquid strikes the liquid-air boundary. [ The critical angle of the liquid = 45o ] 5-26
27. 27. Physics Module Form 4 Chapter 5 - Light GCKL 2011 C the greatest angle of incidence in optically more dense medium D 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 42o. In which diagram does the light move from point O? 15 The diagram shows a light ray travelling from air12 The figure shows a ray of light is incident in air into a plastic block with an angle of incidence ,X. to the surface of Prism A and B. What is the critical angle of the plastic? Which comparison is correct ? 16 The diagram shows a light ray travelling from air A Density of prism A < density of prism B into a glass prism. B Critical angle of prism A < critical angle of prism B C Refractive index of prism A < refractive index of prism B13 The critical angle is A the smallest angle of incidence in optically more dense medium B the smallest angle of incidence in optically less dense medium What is the critical angle of the glass? 5-27
28. 28. Physics Module Form 4 Chapter 5 - Light GCKL 2011 21 The diagram shows a cross- section of a fibre A 40o B 50o optic cable. C 60o D 70o E 80o17 The refractive index of water is 1.33. What is the critical angle of the water. A 44.5o B 46.9o o Which comparison is correct ? C 48.8 D 49.2o E 54.3 o A Density of P < density of Q B Density of P >density of Q18 The refractive index of plastic block is 13 . C Density of P = density of Q 5 What is the value of the cosine of the critical angle of the plastic? A 5 B 12 12 13 C 13 D 5 12 13 E 13 519 The figure shows a ray of light AO traveling in Answer: medium X strikes the medium X-air boundary. [ The refractive index of medium X = 1.12 ] 1 11 2 12 3 13 4 14 5 15 6 16 7 17 8 18 9 19 In which direction does the light move from O ? 10 20 A OE B OD C OC D OB20 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. 29. Physics Module Form 4 Chapter 5 - Light GCKL 2011Section A (c) Name other optical device that applies the(Paper 2) phenomenon in (a)(i).Structure Question: [ 1 mark ]1. 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 2. Figure 4 shows a traveller driving a car on a hot forms the inner core, Y is surrounded by another day. The traveller sees a type of glass which forms the outer layer, X. 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? a) Which part of the air is denser? ………………………………………………………… [ 1 mark ] ( 1 mark ) (ii) Compare the refractive index of outer layer X and inner core Y. 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 ] ………………………………………………………… ( 1 mark ) (b) The refractive index of inner core Y is 2.10. Calculate the critical angle of the inner core Y. c) i) What is the phenomenon occurring at point X ……………………………………………………..… [ 2 marks ] (1 mark ) ii) What is the puddle of water actually? ………………………………………………………… ( 1 mark ) 5-29
30. 30. Physics Module Form 4 Chapter 5 - Light GCKL 2011d) 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 aperiscope works: (critical angle of glass = 42o) Glass object prism tctct Eye e 5-30
31. 31. Physics Module Form 4 Chapter 5 - Light GCKL 2011 5.4 U N D E R S T A N D I N G L E N S E SIntroduction 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 (b) ………………lens, also known as converging lens. diverging lens. It …………………….at the centre of the lens. It is ………………….at the centre of the lens. Convex lens Concave lensState thedifferencesbetween convexlens and concavelens When light ray which are parallel and close to When light rays are parallel to the principle the principle axis …….. on a convex lens, they axis …… on a concave lens., they are ……….. are ………… and ............... to a point, F on the and appear to …………. from the …………… principle axis. This point is a ………….. of the on the principle axis. convex lens.Common 1. The focal point, F is a point on the …………………….where all rays are ……………….andterminology of ……………………..to the axis that ………………………to it after passing through a convexreflection of light lens, or appear to ………………………..from it after passing through a concave lens.on a curved mirror 2. 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. 32. Physics Module Form 4 Chapter 5 - Light GCKL 2011Construction rules Rule 1:of convex lens 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 Using the principles of construction of ray diagram, complete the ray diagrams for each of theconvex lens 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 Application: image: 1. 1. 2. 2. 3. 4. B u = f ( Object, O is at F ) Characteristics of Application: image: 1. 1. 2. 3. 4. 5-32
33. 33. Physics Module Form 4 Chapter 5 - Light GCKL 2011 C f < u < 2f or f < u < r ( Object O is Characteristics of Application: between F and C image: 1. 1. 2. 2. 3. 3. 4. 4. D u = 2f or u = r ( Object ,O is at C) Characteristics of Application: image: 1. 1. 2. 3. 4. Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of Application: image: 1. 1. 2. 2. 3. 3. F u =  ( Object ,O very far from the lens) Characteristics of Application: image: 1. 1. 2. 2. 3. 3. 5-33
34. 34. Physics Module Form 4 Chapter 5 - Light GCKL 2011Construction rulesof 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 : Virtual, upright and diminished.Image formed by Using the principles of construction of ray diagram, complete the ray diagrams for each of theconvex mirror: cases shown below: u = object distance; v = image distance ; f = focal length A u < f ( Object between F and P ) Characteristics of Application: image: 1. 1. 2. 2. 3. (B ) f<u <2f (Object at between f and 2f) Characteristics of Application: image: 1. 1. 2. 2. 3. 5-34
35. 35. Physics Module Form 4 Chapter 5 - Light GCKL 2011Power of lenses Power of a lens = 1 . Focal length The unit of power of a lens is Dioptre (D) or m-1 or P = 1 @ P = 100 Convex lens : the power is taken to be f f( cm) positive Concave lens : the power is taken to be negative f = focal length Linear Magnification (m) :The linearmagnification , mdefine as: Where f = focal length u = object distance v = image distance m = linear magnificationLens Formula ho = object height hi = image heightSign Conventions Type of lenses Convex lens Concave lens Object distance ,u Always + Always + Object is always placed to the Object is always placed to the left of the lens left of the lens Image distance, v + if the image is real ( image + if the image is real ( image is formed on the right side of is formed on the right side of the lens. the lens - if the image is virtual - if the image is virtual ( image is formed on the left ( image is formed on the left side of the lens). side of the lens). Focal length, f Always + Always - Power of length, P Always + Always - Linear magnification, m Size of image ImI =1 Image and object are the same size ImI >1 Enlarged image ImI <1 Diminished image 5-35
36. 36. Physics Module Form 4 Chapter 5 - Light GCKL 2011Meaning of real A real imge is one which can be cast on a A virtual imge is one which cannot be cast on aimage and virtual screen. screen.imageCheck 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 ray2 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? 5 Which of the following is true?3 The diagram shows parallel rays of light passing through a liquid in glass container. A The unit of the power of lens is Watt [ The refractive index of the liquid = 1.35 ] 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. 37. Physics Module Form 4 Chapter 5 - Light GCKL 20116 Diagram shows light rays passing through a 10 Figure shows four light rays A,B,C and D passing convex lens . 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 11 What is the power of a convex lens which has a D Optical length focal length 50 cm ?7 The diagram shows the action of a magnifying A -0.2 D B 0.2 D glass. C -2.0 D D 2.0 D Which point is the principal focus of the lens? E 4.0 D 12 The power of a lens is - 40 D. What is the type of the lens and its focal length? Type of length Focal length 2 A Concave lens -2.5 x 10 m -2 B Concave lens -2.5 x 10 m8 The diagram shows an image ,I is formed by a 2 C Convex lens -2.5 x 10 m convex lens. D Convex lens -2.5 x 10-2 m Where is the position of the object? 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 A less than f9 The diagram shows an image ,I is formed by a B between f and 2f concave lens. C same as 2f Where is the position of the object? D 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