CHAPTER 9. Knowledge. (d) 3 2 l

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1 CHAPTER 9 Review K/U Knowledge/Understanding T/I Thinking/Investigation C Communication A Application Knowledge For each question, select the best answer from the four alternatives. 1. Water waves splash under a dock at regular intervals. The time that elapses between splashes is called the (a) incidence (b) frequency (c) specular (d) period (9.1) K/U 2. A water wave has a frequency of 0.20 Hz. How many wavelengths will have passed a fixed point after 1.5 min? (9.1) K/U (a) 12 (b) 18 (c) 90 (d) If a beam of light strikes a surface exactly perpendicular to the surface, then the angle of incidence is (a) 08 (b) 458 (c) 608 (d) 908 (9.1) K/U 4. In terms of light, which quantity remains constant regardless of the medium through which it travels? (9.2) K/U (a) wavelength (b) frequency (c) amplitude (d) speed 5. Visible light is one example of (a) an electromagnetic wave (b) a longitudinal wave (c) an acoustic wave (d) a compression wave (9.1) K/U 6. A ray of light refracts when travelling from medium 1 into medium 2. The angle of incidence is less than the angle of refraction. Select the true statement concerning this interaction. (9.2) K/U (a) Medium 1 must be a vacuum. (b) The speed of the light ray increases as it enters medium 2. (c) The frequency of the light ray decreases as it enters medium 2. (d) Medium 1 has a lower index of refraction. 7. Which interaction will exhibit the greatest amount of dispersion? (9.2) K/U (a) white light entering water at a small angle of incidence (b) white light entering water at a large angle of incidence (c) white light entering a diamond at a small angle of incidence (d) white light entering a diamond at a large angle of incidence 8. Predict what will happen as two water waves move toward each other. (9.3) K/U (a) The waves will bounce off each other and return in the opposite direction. (b) The waves will momentarily add together and then continue on in their original direction. (c) The waves will collide and cancel each other s energy. (d) The waves will scatter off each other, moving perpendicular to their original direction. 9. At any point on one of the nodal lines in the two-point-source interference pattern, (a) a wave crest is combining with a wave trough (b) a wave crest is combining with a wave crest (c) a wave crest is combining with a slightly smaller wave crest (d) a wave crest is reflecting off a wave crest (9.3) K/U 10. A teacher uses audio speakers to create a twopoint-source interference pattern in the classroom. The speakers are placed at S 1 and S 2. A student stands at point P on the n = 1 nodal line. In terms of the wavelength, l, what is the path length difference between PS 1 and PS 2? (9.3) K/U (a) There is no path length difference. (b) 1 2 l (c) l (d) 3 2 l 11. Which action will decrease the angular separation of nodal lines in a two-point-source interference pattern? (9.3) K/U (a) moving the point sources farther apart (b) decreasing the frequency of the waves (c) increasing the wavelength of the waves (d) decreasing the screen distance 494 Chapter 9 Waves and Light NEL

$4) K/U (a) propagation (b) reflection (c) radiation pressure (d) diffraction Indicate whether each statement is true or false. If you think the statement is false, rewrite it to make it true. 13.$

2 12. Newton s particle theory of light is unable to account for which phenomenon? (9.4) K/U (a) propagation (b) reflection (c) radiation pressure (d) diffraction Indicate whether each statement is true or false. If you think the statement is false, rewrite it to make it true. 13. The angle of incidence is measured between the incoming ray and the reflecting surface. (9.1) K/U 14. The amplitude of a water wave is the vertical distance from the top of a crest to the bottom of a trough. (9.1) K/U 15. The critical angle is small for substances that have large indices of refraction. (9.2) K/U 16. The dependence of the speed of light on wavelength is called interference. (9.2) K/U 17. The index of refraction is the same for red and blue light in the same material. (9.2) K/U 18. In any situation, the angle of incidence is always greater than the angle of refraction. (9.2) K/U 19. Light moves faster in a quartz crystal than it does in a diamond. (9.2) K/U 20. As a light wave refracts from air into glass, the only quantity to remain constant is the light s wavelength. (9.2) K/U 21. The symbol c is used in reference to the speed of light in air at standard temperature and pressure. (9.2) K/U 22. Two sources that produce waves of the same frequency and phase are said to be coherent. (9.3) K/U 23. Diffraction of waves decreases as the width of the slit decreases. (9.3) K/U 24. Destructive interference occurs along a nodal line. (9.3) K/U 25. Light waves diffract a greater amount than sound waves. (9.3) K/U 26. Newton s corpuscular theory of light had no explanation for the small amount of diffraction displayed by visible light. (9.4) K/U 27. Huygens wave principle states that all points on a wave front can be thought of as new sources of spherical waves. (9.4) K/U 28. Calculations with Young s experiment can be used to determine the wavelength of a light source or the slit spacing of a double slit. (9.5) K/U 29. For angles of less than 108, the sine and the cosine of the angle are approximately equal. (9.5) K/U 30. An advantage of fibre optic technology is that large amounts of information can be transmitted over short distances. (9.6) K/U Match each term on the left with the most appropriate description on the right. 31. (a) refraction (b) diffraction (c) interference (d) dispersion (e) critical angle (f) reflection (g) angle of refraction Understanding 32. Use unit analysis to show that the quantity n 2 sin u 2 in Snell s law has no units. (9.1) K/U A 33. (a) Explain why a laser beam is invisible when it travels through the air, but can be seen as it strikes a white screen. (b) Describe how one could make the laser beam visible in the air, as in Figure 1. (9.1) K/U A Figure 1 (i) two waves in the same medium interact (ii) the smallest angle of incidence at which a light ray can be totally reflected from the boundary between two media (iii) the angle that a light ray makes with respect to the normal to the surface when it has entered a different medium (iv) a change in direction of a light ray when it meets an obstacle (v) the bending of a wave when it passes through an opening (vi) separation of a wave into its component parts according to a given characteristic (vii) the bending of light as it travels from one medium to another (9.1, 9.2, 9.3) K/U NEL Chapter 9 Review 495

34. Explain using a diagram and words how absolutely still water can exhibit specular reflection while choppy water exhibits diffuse reflection. (9.1) T/I C A 35.

(9.4) K/U C 37. Explain how Young s double-slit experiment demonstrated that light has the properties of a wave. (9.5) C 38. List the benefits and drawbacks of fibre optic cables. (9.6) K/U C Analysis and Application 39.

A certain radio station broadcasts with a frequency of 88.7 MHz. Radio waves travel at the speed of light (3.0 3 10 8 m/s). Determine the wavelength of these radio waves. (9.1) T/I 41.

3 34. Explain using a diagram and words how absolutely still water can exhibit specular reflection while choppy water exhibits diffuse reflection. (9.1) T/I C A 35. Explain the separation of light into colours as light travels through a prism (Figure 2). (9.2) K/U Figure Summarize the key differences between Newton s particle theory and Huygen s principle. (9.4) K/U C 37. Explain how Young s double-slit experiment demonstrated that light has the properties of a wave. (9.5) C 38. List the benefits and drawbacks of fibre optic cables. (9.6) K/U C Analysis and Application 39. The wavelength of red light is approximately 650 nm. How many wavelengths of red light will fit across the width of a 1.0 cm fingernail? (9.1) T/I 40. A certain radio station broadcasts with a frequency of 88.7 MHz. Radio waves travel at the speed of light ( m/s). Determine the wavelength of these radio waves. (9.1) T/I 41. A light year is defined as the distance light travels in one year, and is useful for astronomical measurements. Alpha Centauri, the nearest star system to our own, is 4.4 light years away. Determine the distance to Alpha Centauri in metres. (9.1) T/I 42. A Pyrex test tube submerged in vegetable oil becomes invisible (Figure 3). Use refraction to explain this illusion. (9.2) T/I A 43. The Cassini Space Probe entered into orbit around Saturn in July On average, Saturn is about 1.1 billion kilometres away from Earth. How many hours does it take for a message travelling at the speed of light to reach Earth from Cassini? (9.1) K/U 44. A beam of light refracts from air into Plexiglas. The index of refraction for Plexiglas is Determine the speed of the light in the Plexiglas. (9.2) K/U 45. The speed of light is reduced by 45 % as it refracts from a vacuum into an unknown transparent material. Calculate the index of refraction of the transparent material. (9.2) T/I 46. The beam of a green laser travels from air into Pyrex, then into water. Calculate the wavelength, in nanometres, of the green light in the Pyrex and in the water. The index of refraction for Pyrex is 1.47, the index of refraction for air is , and the index of refraction for water is The wavelength of the green laser is m. (9.2) T/I 47. A ray of monochromatic light in water hits quartz crystal at an incident angle of Determine the angle of refraction. The index of refraction for quartz crystal is (9.2) K/U 48. A ray of light in the air hits a block of transparent material at an incident angle of 628. The angle of refraction is 448. (9.2) T/I C (a) Sketch the situation, labelling the incident ray, the refracted ray, the reflected ray, and the normal. (b) Determine the index of refraction of the transparent block. (c) Determine the speed of light in the block. 49. A ray of monochromatic light travelling in air strikes the end of a 21 cm wide block of Plexiglas at an incident angle of 658 (Figure 4). The index of refraction for Plexiglas is (9.2) K/U T/I (a) Calculate the angle of refraction as the light enters the block. (b) The light travels to the opposite side of the block and refracts out into the air. The path of the refracted light ray is parallel to the original light ray, but displaced a distance d. Calculate the value of d cm 10 cm Figure 3 d Figure Chapter 9 Waves and Light NEL

4 50. A right-triangular prism has edge lengths of 3.0 cm, 4.0 cm, and 5.0 cm. A ray of red light in air hits the 3.0 cm edge at an incident angle of 0.08 (Figure 5). The prism is made of flint glass, which has an index of refraction of 1.65 for red light. (9.2) T/I Figure cm 5.0 cm 4.0 cm (a) Calculate the angle of deviation of the light beam from its original path after it leaves the prism. The angle of deviation is the angle between the incident ray and the final outgoing ray. (b) Calculate the angle of deviation if a beam of violet light was used. Violet light has an index of refraction of 1.67 in flint glass. 51. Determine the critical angle of the following interfaces. The index of refraction for Pyrex is 1.47, for air it is , and for water it is (9.2) T/I (a) Pyrex to air (b) Pyrex to water (c) water to air 52. A ray of light travels from air into an optical fibre with an index of refraction of (9.2) K/U T/I (a) In which direction does the light bend? (b) The angle of incidence on the end of the fibre is 338. Determine the angle of refraction inside the fibre. 53. A ray of light travels through a liquid. The speed of light in the liquid is m/s, and the wavelength of the light ray in the liquid is 440 nm. Determine the following values. (9.2) T/I (a) the index of refraction of the liquid (b) the wavelength of the light ray in a vacuum 54. The index of refraction of ethyl alcohol is Calculate the critical angle for a light ray travelling from ethyl alcohol into air. (9.2) K/U 55. Calculate the critical angle for a glycerin and water interface. The index of refraction for glycerin is 1.47 and for water is (9.2) K/U 56. Calculate the critical angle for a diamond and crown glass interface. The index of refraction for diamond is 2.42, and for crown glass is (9.2) K/U 57. A small light source shines upward from the bottom of a 35 cm deep pond. When viewed from above, because of internal reflection, the light source makes a disc of light on the water s surface. Calculate the diameter of this disc. (9.2) T/I 58. A student uses a laser beam and a semicircular acrylic block to study refraction. Light is incident on the block at the following increasing angles, 158, 308, 458, and 608. The student measures the refracted angles as 118, 218, 298, and 388, respectively. (9.2) K/U C (a) Use the data to plot a graph showing the sines of the refracted angles versus the sines of the incident angles. (b) Determine the slope of the graph to two decimal places. Use the slope to determine the index of refraction of acrylic to two decimal places. 59. Light with a wavelength of 590 nm passes through double slits with a spacing of mm to a screen located 1.10 m away. Calculate how far apart the bright fringes will be on the screen. (9.5) T/I 60. Discuss the impact of two technologies based on the wave theory of light. Focus on the economic and social impact of the technologies. (9.2, 9.6) K/U A 61. A student uses a ripple tank to create a twopoint-source interference pattern. The student places a dot somewhere along the n 5 2 nodal line. The distances from the dot to each source are 16.3 cm and 21.9 cm. Determine the wavelength of the waves. (9.3) T/I 62. Two coherent point sources 4.5 cm apart create an interference pattern in a ripple tank. There are 10 nodal lines in the entire interference pattern. Determine the wavelength of the water waves. (9.3) T/I 63. Water waves hit a straight barrier with two small openings separated by 14 m. Waves diffract from the openings and interfere with each other, creating a pattern containing a total of 12 nodal lines. Determine the wavelength of the water waves. (9.3) T/I 64. Two sources are vibrating at the same frequency in phase a distance apart in a ripple tank. How would you change each of the following to increase the number of nodal lines? (9.3) T/I (a) frequency (b) wavelength (c) separation of the sources 65. Two sources are 7.2 cm apart and vibrate in phase at 7.0 Hz. A point on the third nodal line is 30.0 cm from one source and 37 cm from the other. (9.3) K/U T/I (a) Calculate the wavelength of the waves. (b) Calculate the speed of the waves. 66. Two towers of a radio station are 400 m apart along an east west line. The towers act as point sources radiating at a frequency of Hz. Radio waves travel at a speed of m/s. Determine the first angle at which the radio signal strength is at a maximum for listeners who are on a line 20.0 km north of the station. (9.5) T/I A NEL Chapter 9 Review 497

5 67. Two coherent point sources 14 cm apart create an interference pattern in a ripple tank. The frequency of the waves is 3.1 Hz, and the waves travel 30.0 cm in 1.8 s. (9.3) T/I (a) Determine the wavelength of the waves. (b) Determine the total number of nodal lines in the entire interference pattern that may be observed. 68. List the successes and failures of the particle and wave models in accounting for the behaviour of light as follows: (9.4) K/U T/I (a) Name three optical phenomena adequately accounted for by both models. (b) Name two optical phenomena not adequately accounted for by the particle model. (c) Name one phenomenon not adequately accounted for by the wave model. 69. Describe and explain the experimental evidence collected up to the end of this chapter in support of the wave theory of light. (9.4) K/U T/I 70. Red laser light (l nm) passes through a double slit of unknown slit spacing. The third bright fringe is observed at an angle of Determine the slit spacing, in millimetres. (9.5) T/I 71. Red laser light (l nm) passes through a double slit, and the slits are spaced m apart. Predict the distance between adjacent bright fringes when the light hits a screen positioned 5.0 m away from the slits. (9.5) T/I 72. Violet laser light of unknown wavelength passes through two slits that are spaced m apart. A distance of 4.3 mm separates each bright fringe on a screen 6.5 m from the slits. Calculate the wavelength of the violet light, in nanometres. (9.5) T/I 73. A group of students uses an intense white light and a red filter to create bright fringes in a double-slit experiment. Describe the differences in the observed results when the students make the following changes, and explain the differences. (9.5) T/I A (a) Move the screen farther from the slits. (b) Temporarily block one of the slits. (c) Replace the red filter with a green filter. (d) Remove the filter and use white light. 74. In a double-slit experiment using a monochromatic source, the recorded distance between the first and seventh nodal lines is 6.0 cm. The slit separation is m, and the screen is 3.0 m from the slits. Calculate the wavelength of the light. (9.5) T/I 75. Two slits produce an interference pattern. The perpendicular distance from the midpoint between the two slits to the screen is 7.7 m. The two thirdorder maxima are separated from each other by a distance of m. The wavelength of the light is m. Calculate the separation between the slits. (9.5) T/I 76. A double-slit experiment uses two slits 0.35 mm apart to produce an interference pattern on a screen 1.5 m from the slits. Determine the wavelength of the incident light. The distance between adjacent bright spots is 2.4 mm. (9.5) T/I 77. Light of wavelength m shines on a slide containing two slits at a separation of mm that is 1.0 m away from a screen. Determine the distance between two consecutive bright bands on an interference pattern. (9.5) T/I 78. Calculate the wavelength of the light that produces dark fringes m apart on a screen 1.25 m away after passing through two slits that are spaced mm apart. (9.5) T/I 79. A pattern of fringes appears on a screen 175 cm away, with a spacing of 7.7 mm between bright fringes. The wavelength of the light is m. Determine the slit spacing. (9.5) T/I 80. Light with a wavelength of 530 nm shines on a double-slit apparatus. The bright fringes that appear on a distant screen have an angular separation of Determine the separation between the slits. (9.5) T/I 81. Two cellphone towers separated by 550 m transmit an identical 790 MHz signal. You discover that you have an optimal signal while standing 12 km from each of the towers. The towers lie along a north south line, and as you walk directly north, the signal decreases. Calculate how far north you must walk until you have an optimal signal again. (9.5) T/I A 82. A light source shines light of wavelengths 490 nm and 560 nm onto a pair of slits separated by 0.44 mm. Calculate the angular location and the location in centimetres of the second-order dark fringes on a screen 1.4 m from the slits. (9.5) C T/I Evaluation 83. Draw two flat mirrors at right angles to each other. Use the law of reflection to show that as a wave bounces off both surfaces, the wave undergoes a full 1808 reversal of direction. (9.1) C A 498 Chapter 9 Waves and Light NEL

84. Imagine that a friend tells you about his plans for a special room in a haunted house. Your friend says, I could put a tank of water at the end of a hallway and hide underwater with a diving mask.

6 84. Imagine that a friend tells you about his plans for a special room in a haunted house. Your friend says, I could put a tank of water at the end of a hallway and hide underwater with a diving mask. If I choose a spot at the end of the tank, light rays travelling from me toward people in the hallway will reflect internally along the water surface. The people in the hallway will not see me, but I will see them and can jump out and scare them! Assess the plan s chances of success. (9.2) T/I C A 85. Design a procedure to determine the wavelength of water waves that uses a ripple tank, two point sources, and other laboratory equipment. (9.3) T/I C A 86. Imagine that you are standing a few kilometres from a radio tower, with the wall of a tall building covered in metallic siding a few hundred metres directly behind you as you face the tower. (The siding will reflect radio waves.) A friend hands you a radio tuned to the tower s station with the radio s frequency display covered, and challenges you to guess the frequency. Devise a procedure to determine the station s frequency. (9.3) T/I C A 87. The debate over whether light is a particle or a wave lasted for many years. At any moment during that time, you could find scientists who claimed that light was a particle as well as scientists who claimed that light was a wave. Imagine a time before Young s experiment, and justify the viewpoints of scientists on both sides of the debate. (9.4) C A 88. Use the concepts of reflection and interference to propose why a car radio might lose reception of certain stations at certain places. (9.4) K/U T/I C A 89. A student tries to recreate Young s double-slit experiment by using two closely spaced miniature light bulbs as the light sources. The student does not observe the expected bright and dark fringes. Evaluate the student s experiment. (9.5) T/I A Reflect on Your Learning 90. What did you find most surprising in this chapter, and what did you find most interesting? How can you learn more about these topics? K/U T/I C 91. How would you explain the concepts of total internal reflection, refraction, and diffraction to a fellow student who has not taken physics? K/U T/I C 92. In what areas of your daily experience do you now see the physics concepts that were explored in this chapter? K/U T/I C 93. What properties of waves and light are still confusing to you? How can you improve your understanding of the properties of waves and light? K/U T/I C Research WEB LINK 94. Research the working and use of fibre optic technology. Identify purposes, and illustrate the positions of the core, the cladding, and the buffer coating. List at least five advantages of a fibre optic communication system over a traditional metal wire system and discuss with a classmate. T/I C A 95. Night-vision goggles allow their user to see infrared light using technology known as thermal imaging. Research thermal imaging and its impact on society. Explain how this technology uses the wave nature of light. Identify other uses of thermal imaging besides night vision. Summarize your findings in a short report. C A 96. Modern double-slit experiments often make use of lasers to provide a coherent light source. Research current technology used for double-slit experiments and any applications of double-slit interference effects. Summarize your results in a short statement. C A 97. Light-based technologies can be used to analyze human skin for medical and cosmetic concerns. T/I C A (a) Investigate optics-based skin technologies and summarize how they work. (b) Identify the light-based technology used in optics-based skin analysis. (c) Discuss some of the benefits and drawbacks of this type of skin analysis. (d) List two careers associated with optics-based skin analysis and describe the pathways to each of these careers. 98. The colour theory of vision is based on the particle theory of light. Research this theory, and explain some of its successes and shortcomings. T/I A 99. Research heat mirages, and discuss how the refraction of light can cause mirages to appear in the distance on a paved road on a warm summer day or in a desert (Figure 6). K/U T/I C A Figure Research the work of Francesco Grimaldi ( ) and his contributions to the theory of light. K/U T/I C A (a) Summarize Grimaldi s observations relating to light. (b) Using Grimaldi s work as an example, express how new theories change scientific thought. NEL Chapter 9 Review 499

9.4 Light: Wave or Particle?

9.4 Light: Wave or Particle? Huygens principle every point on a wave front can be considered as a point source of tiny secondary wavelets that spread out in front of the wave at the same speed as the wave itself rectilinear propagation