REVIEW
Teaching Resources
• TeacherEXPRESS
• Virtual Physics Lab 26
• Conceptual Physics Alive!
   DVDs Reflection and
   Refraction
9 REVIEW
Concept Summary
••••••
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Key Terms
reflection (p. 579)
normal (p. 580)
angle of incidence
   (p. 580)
angle of reflection
   (p. 580)
law of reflection
   (p. 580)
virtual image
   (p. 581)
diffuse reflection
   (p. 582)
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When a wave reaches a boundary be-
tween two media, usually some or all
of the wave bounces back into the first
medium.
The law of reflection states that the angle
of incidence and the angle of reflection
are equal to each other.
Plane mirrors produce only virtual
images.
When light is incident on a rough sur-
face, it is reflected in many directions.
Sound energy that is not reflected is
absorbed or transmitted.
When a wave that is traveling at an angle
changes its speed upon crossing a bound-
ary between two media, it bends.
Sound waves are refracted when parts of
a wave front travel at different speeds.
Changes in the speed of light as it passes
from one medium to another, or varia-
tions in the temperatures and densities of
the same medium, cause refraction.
A mirage is caused by the refraction of
light in Earth’s atmosphere.
Since different frequencies of light travel
at different speeds in transparent materi-
als, they will refract differently.
In order for you to see a rainbow, the
sun must be shining in one part of the
sky, and water droplets must be in the
opposite part of the sky.
Total internal reflection occurs when the
angle of incidence is larger than the criti-
cal angle.
reverberation
   (p. 583)
refraction (p. 585)
wave front (p. 585)
mirage (p. 588)
dispersion (p. 590)
critical angle (p. 594)
total internal
   reflection (p. 594)
optical fiber (p. 595)
think! Answers
29.2
The color of the image will be the same
as the color of the object because the
frequency of light is not changed by
reflection.
You’ll hear the whistle better if the wind
speed near the ground is less than the wind
speed higher up. For this condition, the
sound will be refracted toward the ground.
No! There would be no refraction if light
traveled at the same speed in air of differ-
ent temperatures and densities.
29.7
29.9
29.11.1 No. If there is no change in speed, there
        is no refraction. If there is no refraction,
        there is no dispersion of light and hence,
        no rainbow!
29.11.2 Your arm describes a cone, and your
        finger sweeps out a circle. Likewise with
        rainbows.
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9 ASSESS
Check Concepts
Section 29.1
••••••
ASSESS
Check Concepts
9. What is meant by the idea that a surface
   may be polished for some waves and rough
   for others?
Section 29.5
1. What becomes of a wave’s energy when
   the wave is totally reflected at a boundary?
   When it is partially reflected at a boundary?
2. Why do smooth metal surfaces make good
   mirrors?
3. When light strikes perpendicular to the
   surface of a pane of glass, how much light
   is reflected and how much is transmitted at
   the first surface?
Section 29.2
10. Distinguish between an echo and a
    reverberation.
11. Does the law of reflection hold for both
    sound waves and light waves?
Section 29.6
12. Distinguish between reflection and
    refraction.
13. When a wave crosses a surface at an angle
    from one medium into another, why does
    it change directions as it moves across the
    boundary into the new medium?
14. What is the orientation of a ray in relation
    to the wave front of a wave?
Section 29.7
4. What is meant by the normal to a surface?
5. What is the law of reflection?
Section 29.3
6. When you view your image in a plane mir-
   ror, how far behind the mirror is your image
   compared with your distance in front of the
   mirror?
15. Give an example where refraction is abrupt,
    and another where refraction is gradual.
Section 29.8
16. Does refraction occur for both sound waves
    and light waves?
17. If light had the same speed in air and in wa-
    ter, would light be refracted in passing from
    air into water?
18. If you can see the face of a friend who is
    underwater, can she also see you?
7. In what way does the law of reflection hold
   for curved mirrors?
Section 29.4
8. In what way does the law of reflection hold
   for diffuse reflection? Explain.
CHAPTER 29
REFLECTION AND REFRACTION
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19. 
9 ASSESS
  ASSESS
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19. Does refraction tend to make objects sub-
    merged in water seem shallower or deeper
    than they really are?
Section 29.12
26. What is the critical angle in terms of refrac-
    tion and total internal reflection?
27. Why are optical fibers often called light
    pipes?
Think and Rank
Think and Rank
••••••
Section 29.9
Rank each of the following sets of scenarios in
order of the quantity or property involved. List
them from left to right. If scenarios have equal
rankings, then separate them with an equal sign.
(e.g., A B)
28. Wheels from a toy cart are rolled from
    a concrete sidewalk onto the following
    surfaces.
       (A) a paved driveway
       (B) a grass lawn
       (C) close-cropped grass (like that on a
           golf-course putting green)
20. Is a mirage a result of refraction or reflec-
    tion? Explain.
21. Is daytime a bit longer or is it a bit shorter
    because of atmospheric refraction?
Section 29.10
22. As light passes through a transparent medi-
    um, it undergoes an absorption-reemission
    process (discussed earlier, in Figure 27.7).
    Which interacts more with the medium,
    light of high frequencies or light of low
    frequencies? (Do high frequencies or low
    frequencies lag behind?)
23. Why does blue light refract at greater angles
    than red light in transparent materials?
Section 29.11
24. What conditions are necessary for viewing a
    rainbow in the sky?
25. How is a raindrop similar to a prism?
Due to slowing, each set of wheels bends at
the boundary and is deflected from its origi-
nal course. Rank the surfaces according to
the amount each set of wheels bends at the
boundary, from greatest amount of bending
to least amount of bending.
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Think and Explain
9 ASSESS
29. Identical rays of light enter three transpar-
    ent blocks composed of different materi-
    als. Light slows upon entering the blocks.
    Rank the blocks according to the speed light
    travels in each, from highest speed to lowest
    speed.
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31. 
32. Suppose that a mirror and three lettered
    cards are set up as in the figure. If a person’s
    eye is at point P, which of the lettered cards
    will be seen reflected in the mirror? Explain.
30. Identical rays of light in air are refracted
    upon entering three transparent materials.
      (A) water, where speed slows to 0.75c
      (B) ethyl alcohol (speed 0.74c)
      (C) crown glass (speed 0.66c)
33. In the photograph below we see the bird
    and its reflection. Why don’t we see the
    bird’s feet in the reflection?
Rank the materials according to how much
the light ray bends toward the normal, from
most bending to least bending.
34. Contrast the types of reflection from a
    rough road and from the smooth surface of
    a wet road to explain why it is difficult for
    a motorist to see the roadway ahead when
    driving on a rainy night.
35. Cameras with automatic focus bounce
    a sonar (sound) beam from the object
    being photographed and compute distance
    from the time interval between sending and
    receiving the signal. Why will these cameras
    not focus properly for photographs of
    mirror images?
CHAPTER 29
REFLECTION AND REFRACTION
Think and Explain
••••••
31. On a steamy mirror, wipe an area just large
    enough to allow you to see your full face.
    How tall will the wiped area be compared
    with the vertical dimension of your face?
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36.
9 ASSESS
  ASSESS
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36. In the photograph below, Peter Hopkinson
    is standing astride a large mirror and boosts
    class interest with this zany demonstration.
    How does he accomplish his apparent levi-
    tation in midair?
41. The photo below shows two identical cola
    bottles, each with the same amount of cola.
    The right bottle is in air, and the left bottle
    is encased in solid plastic that has nearly the
    same index of refraction as glass (the speed
    of light in the plastic and in glass are nearly
    the same). Which bottle shows an illusion
    of the amount of cola? How does the other
    bottle give a truer view of its contents?
37. Why is an echo weaker than the original
    sound?
38. Suppose you are standing downwind from
    a barking dog on a windy day. The wind
    blows faster well above the ground than
    close to the ground. Refraction will change
    the sound of the dog’s bark. Will the sound
    of the bark be somewhat louder or some-
    what diminished? Defend your answer.
39. Does the reflection of a scene in calm water
    look exactly the same as the scene itself only
    upside down? (Hint: Place a mirror on the
    floor between you and a table. Do you see
    the top of the table in the reflected image?)
40. If you were spearing a fish with a spear,
    would you aim above, below, or directly
    at the observed fish to make a direct hit?
    Would your answer be the same if you used
    laser light to “spear” the fish? Defend your
    answer.
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42. How do the different speeds of light in
    thin air and dense air affect the length of
    daylight?
43. Very short pulses of red light and blue light
    enter a glass block normal to its surface at
    the same time. Which pulse exits first?
44. When you stand with your back to the sun,
    you see a rainbow as a circular arc. Could
    you move off to one side and then see the
    rainbow as the segment of an ellipse rather
    than the segment of a circle (such as Figure
    29.26 suggests)? Defend your answer.
45. A rainbow viewed from an airplane may
    form a complete circle. Will the shadow
    of the airplane appear at the center of the
    circle? Explain with the help of Figure 29.26.
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9 ASSESS
46. Two observers standing apart from each
    other do not see the same rainbow. Explain.
47. Why is a secondary rainbow dimmer than
    the primary bow?
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Think and Solve
Activities
••••••
Think and Solve
••••••
48. When light strikes glass perpendicularly,
    about 4% of the light is reflected at each
    surface. Show that the amount of light
    transmitted through a pane of window
    glass is approximately 92%.
49. Suppose you walk toward a mirror at 1 m/s.
    How fast do you and your image approach
    each other? (The answer is not 1 m/s.)
50. A radio wave sent into space strikes an
    asteroid and is reflected back to Earth
    1 second after being emitted. How far away
    is the asteroid?
51. A spider hangs by a strand of silk at eye level
    20 cm in front of a plane mirror. You are
    behind the spider, 50 cm from the mirror.
    Show that the distance between your eye
    and the image of the spider in the mirror is
    70 cm.
52. The average speed of light slows to 0.75c
    when it enters a particular piece of plastic.
    a. What change occurs in the frequency of
       light in the plastic?
    b. What change occurs in the wavelength?
53. Stand in front of a mirror and put two
    pieces of tape on the glass: one piece where
    you see the top of your head, and the other
    where you see the bottom of your feet.
    Compare the distance between the pieces of
    tape with your height. If a full-length mirror
    is not handy, use a smaller mirror and find
    the minimum length of mirror to see your
    face. Mark where you see the top of your
    head and the bottom of your chin. Then
    compare the distance between the marks
    with the length of your face. What must be
    the minimum length of a plane mirror in
    order for you to see a full view of yourself?
54. What effect does your distance from the
    mirror have on the answer to Activity 53?
    (Hint: Move closer and farther from your
    initial position. Be sure the top of your
    head lines up with the top piece of tape.
    At greater distances, is your image smaller
    than, larger than, or the same size as the
    space between the pieces of tape?) Are you
    surprised?
55. Look at a diamond under bright light. Turn
    the stone and note the flashes of color that
    refract, reflect, and refract toward you.
    When the flash encounters only one eye
    instead of two, your brain registers it differ-
    ently than for both eyes. The one-eyed flash
    is a sparkle! What causes the brilliant
    sparkle of a diamond?
Activities
Teaching Resources
More Problem-Solving Practice
Appendix F
CHAPTER 29
REFLECTION AND REFRACTION
• Computer Test Bank
• Chapter and Unit Tests
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