Unit 12 AP Review Questions: General Light and Optics
Indices of Refraction
Medium / n / Medium / nVacuum / 1.00 / Crown glass / 1.52
Air / 1.0003 / Quartz / 1.54
Water / 1.33 / Flint Glass / 1.61
Ethanol / 1.36 / Diamond / 2.42
Conceptual Problems
1. Sound doesn’t travel through a vacuum. How do we know that light does?
2. List the electromagnetic spectrum from lowest to highest frequency.
3. What does “c” stand for in c = fλ?
4. What colors does white light consist of?
5. Why do black objects appear black?
6. What are the three primary colors of light?
7. What are the three secondary colors of light and how are they produced?
8. List the colors of light in the order of increasing
a. wavelength.
b. frequency.
9. What happens to the wavelength of light in air as the frequency of the light increases?
10. What color would a yellow banana appear when illuminated by
White light?
Green light plus red light?
Blue light?
11. You put a piece of red cellophane (absorbs everything but red) over one flashlight and green cellophane over another. You shine the two beams on a white wall. What color will you see where the two beams overlap?
12. What if you put the red cellophane over the green and shine the light on the wall….what color would you see?
13. Distinguish between transparent, translucent, and opaque objects.
14. What happens to light as it passes through a polarizing filter?
15. What’s the difference between a luminous body and an illuminated body?
16. Is a light bulb luminous or illuminated? Can it be both? Explain.
17. Why can we see non-luminous objects?
18. What is the amount of illumination on a surface directly proportional to? Inversely proportional?
19. A light is 2m from screen A and 4m from screen B. How does the illumination of screen B compare to the illumination of screen A?
20. How does regular/smooth reflection differ from diffuse/irregular reflection?
21. Does the law of reflection apply for diffuse reflection?
22. What is meant by “the normal” to a surface?
23. What are the units for the index of refraction?
24. Compare the angle of incidence with the angle of refraction
a. when a light ray passes from air into glass.
b. when light passes from glass into air.
25. What is the critical angle of incidence?
26. What happens to a ray of light that hits a boundary at an angle greater than the critical angle?
27. How does the speed of light in a substance change as the index of refraction of a substance increases?
28. How does a virtual image differ from a real image?
29. Can very sensitive photographic film detect a virtual image? Explain.
30. How can you prove to someone that an image is a real image?
31. Describe the image produced by a plane mirror.
32. If you’re standing 2m in front of a plane mirror and want to take a picture of yourself (your image), at what distance should the camera lens be focused?
33. An object is located beyond the center of curvature of a concave mirror. Make a ray diagram to locate and describe the image.
34. Make a ray diagram to locate and describe the image produced by a concave mirror when the object is located at the center of curvature.
35. An object is located between the center of curvature and the focal point of a concave mirror. Make a ray diagram to locate and describe the image.
36. An object is located on the focal point of a concave mirror. Make a ray diagram to locate and describe the image.
37. An object is located in front of the focal point of a concave mirror. Make a ray diagram to locate and describe the image.
38. An object is located in front of a convex mirror. Make a ray diagram to locate and describe the image.
39. Suppose you stand in front of a spherical mirror (either concave or convex). Is it possible for your image to be
a. real and upright?
b. virtual and inverted? Justify your answers.
40. Which kind of spherical mirror, concave or convex, can be used to start a fire with the rays from the sun? Explain.
41. An object produces a virtual image in a concave mirror. Where is the object located?
42. Describe the image that will always be produced by a convex mirror.
43. Why are convex mirrors used as side view mirrors in cars? Why wouldn’t it make sense to use concave mirrors for this purpose? Explain.
44. What is the main physical difference between a converging and diverging lens?
45. Make a ray diagram to locate and describe the image produced by an object that is beyond 2f of a convex lens.
46. Make a ray diagram to locate and describe the image produced by an object that is between 2f and f of a convex lens.
47. Make a ray diagram to locate and describe the image produced by an object that is on f of a convex lens.
48. Make a ray diagram to locate and describe the image produced by an object that is in front of f of a convex lens.
49. To produce an image from a movie projector onto a screen, the film is placed between f and 2f of a convex lens. This produces a real, inverted image. Why are the people on the screen right-side-up?
Problems
50. Light takes 1.28 s to travel from the moon to Earth. What is the distance between them? (3.84 E8 m)
51. A ray of light strikes a mirror at an angle of 530 to the mirror.
a. What is the angle of reflection? (370)
b. What is the angle between the incident and reflected rays? (740)
52. A ray of light passes from water into crown glass at an angle of 23.20. Find the angle of refraction in the glass. (20.160)
53. Light goes from flint glass into ethanol. The angle of refraction in the ethanol is 250. What is the angle of incidence in the glass? (20.920)
54. What is the critical angle for diamond in air? (24.420)
55. A block of a certain type of glass has a critical angle of 420 in air. What is its index of refraction? (1.49)
56. What is the speed of light in
a. Flint glass? (1.86 E8 m/s)
b. Diamond? (1.24 E8 m/s)
57. A concave mirror has a radius of 20 cm. What is its focal point? (10 cm)
58. An object is 30 cm from a concave mirror of 15 cm focal length. The object is 1.8 cm high.
a. Where and how high is the image? (30 cm, -1.8 cm)
b. Is it real or virtual? (Real --- positive image distance)
c. What is the magnification of the mirror? (-1, the negative means the image is inverted)
59. A 3cm tall object is placed 8 cm in front of a concave mirror of 12 cm focal length.
a. Where and how high is the image? (-24 cm, 9 cm)
b. Is it real or virtual? (Virtual --- negative image distance)
c. What is the magnification of the mirror? (+3, the positive means the image is erect)
60. A 4.0 cm high candle is placed 20.0 cm from a concave mirror having a radius of 32 cm.
a. Where is the image located and what is its height? (80 cm, -16 cm)
b. Is it real or virtual? (real --- positive image distance)
c. What is the magnification of the mirror? (-4, the negative means the image is inverted)
61. A dentist holds a small concave mirror (of radius 4 cm) 1.6 cm from a patient’s tooth to locate a cavity. What is the magnification of the mirror? (5)
62. A 1.5 cm high object is 22.0 cm in front of a convex mirror with a radius of 34 cm.
a. Find the location and the height of the image. (-9.59 cm, 0.65 cm)
b. Is it real or virtual? (virtual---- negative image distance)
63. Shiny lawn spheres placed on pedestals are examples of convex mirrors. If a sphere has a radius of 20 cm and an image is produced by a 12 cm high robin sitting in a tree 150 cm from the sphere, where and how big is the image? (-9.38 cm, 0.75 cm)
64. The focal length of a convex lens is 17 cm. A 3 cm high candle is placed 34 cm in front of the lens.
a. Find the image and its height. (34 cm, -3 cm)
b. Is it real or virtual? (real---positive image distance)
65. A convex camera lens with a focal length of 5 cm is focused on an object 300 cm away. Find the image’s location. (5.08 cm)
66. A slide of a cell is placed 1.2 cm from a convex lens with a focal length of 10 cm.
a. Where is the image formed? (-1.36 cm)
b. Is it real or virtual? (virtual---negative image distance)
c. What is the magnification of the lens? (+1.13, the positive means the image is erect)
67. At night, when it’s dark outside and you are standing in a brightly lit room, it is easy to see your reflection in a window. During the day it is not so easy. Explain.
68. In astronomy, distances are often expressed in light-years. One light-year is the distance traveled by light in one year. The distance to Alpha Centauri, the closest star other than our own sun that can be seen by the naked eye, is 4.3 light-years. How far is this distance in meters? (4.07 E16 m)
69. Neil Armstrong was the first person to walk on the moon. The distance between the earth and the moon is 3.85 x 108 m.
a. Find the time it took for his voice to reach earth via radio waves. (1.28 s)
b. Determine the communication time for the first person who will some day walk on Mars, which is 5.6 x 1010 m from earth at the point of closest approach. (186.67 s)
70. Two astronauts are 1.5 m apart in their spaceship. One speaks to the other. The conversation is transmitted to earth via electromagnetic waves. The time it takes for sound waves to travel at 343 m/s through the air between the astronauts equals the time it takes for the electromagnetic waves to travel to the earth. How far away from the earth is the spaceship? (1.31 E6 m)
71. A ray of light is incident upon a certain type of glass (from air) at 300. The angle of refraction is 19.20. Construct a diagram to show the incident and refracted rays. Continue the ray through the glass until it reaches the opposite edge in the glass.
a. Construct a normal at this point and determine the angle the refracted ray is incident upon the opposite edge of the glass.
b. If the material on the opposite side of the glass is air, what angle does the ray leave the glass? (300)
c. How does the angle of the ray leaving the glass compare to the angle of the original ray entering the glass? (the same)
72. A beam of light strikes the flat glass side of a fish aquarium (from the air) at an angle of 400 to the normal. This particular glass has an index of refraction of 1.5.
a. What is the angle of refraction in the glass? (25.380)
b. What is the angle of refraction when the ray leaves the glass and enters the water? (28.910)
73. A thick sheet of plastic, n = 1.500, is used as the side of an aquarium tank. Light reflected from a fish in the water has an angle of incidence of 350 on the plastic. What angle does the light enter the air? Draw a diagram. (49.700)
74. The speed of light in a particular transparent material is 1.9 E8 m/s. A ray of light in air enters the material at an angle of 220. What angle is the ray refracted? (13.720)
75. A glass window (n = 1.49) has a thickness of 4.0 x 10-3 m. How long does it take light to pass perpendicularly through the plate? (1.99 E-11 s)
76. A man is fishing from a dock. If he is using a bow an arrow, should he aim above/in front of the fish, at the fish, or below/in back of the fish, to strike it? Explain (Hint: Draw the path that light will take as it reflects off the fish and enters the air from the water).
77. A light source is located 2m below the surface of a swimming pool and 1.5 m from the edge of the pool. The pool is filled to the top with water. At what angle does the light reaching the edge of the pool leave the water? Draw a diagram...it will help on this one. (52.920)
78. A prism bends violet light more than red light. Based on this information, which of the two colors do you think travels the fastest in a prism?
79. The critical angle for a certain type of glass in air is 410. What is the critical angle if the glass is immersed in water? (610)
80. A glass block (n = 1.60) is immersed in a liquid with a smaller index of refraction. A ray of light within the glass hits the glass-liquid surface at a 65.0° angle of incidence. Some of the light enters the liquid. What is the smallest possible refractive index for the liquid? (1.45)
81. A small statue has a height of 3.5 cm and is placed in front of a concave mirror. The image of the statue is inverted, 1.5 cm tall, and is located 13 cm in front of the mirror. Find the focal length of the mirror. (9.10 cm)
82. A layer of oil (n = 1.45) floats on an unknown liquid. A ray of light shines from the oil into the unknown liquid. The angles of incidence and refraction are, respectively, 65.0° and 53.0°. What is the index of refraction of the unknown liquid? (1.65)
83. A beam of light is traveling in air and strikes a material. The angles of incidence and refraction are 63.0°and 47.0°, respectively. Obtain the speed of light in the material. (2.46 E8 m/s)
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Unit 12 AP Review Problems Reflection, Refraction, Lenses, and Mirrors