30 REVIEW
Concept Summary
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REVIEW
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Teaching Resources
• TeacherEXPRESS
• Virtual Physics Lab 27
think! Answers
30.2 Both Jamie and his cat and the virtual image
     of Jamie and his cat are “objects” for the lens
     of the camera that took this photograph.
     Since the objects are at different distances
     from the camera lens, their respective images
     are at different distances with respect to
     the film in the camera. So only one can be
     brought into focus.
30.4 The object should be (a) at one focal length
     from the lens (at the focal point) (see
     Figure 30.10); (b) and (c) within one focal
     length of the lens (see Figure 30.9); (d) at two
     focal lengths from the lens (see Figure 30.10);
     (e) between one and two focal lengths from
     the lens (see Figure 30.10).
30.8 Different frequencies travel at different speeds
     in a transparent medium, and therefore
     refract at different angles. This produces
     chromatic aberration. Light reflection, on the
     other hand, has nothing to do with the fre-
     quency of light. One color reflects the same as
     any other.
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A lens forms an image by bending rays of
light that pass through it.
The type of image formed by a lens
depends on the shape of the lens and
the position of the object.
The size and location of the object, its
distance from the center of the lens, and
the focal length of the lens are used to
construct a ray diagram.
A converging lens forms either a real or
a virtual image. A diverging lens always
forms a virtual image.
Optical instruments that use lenses in-
clude the camera, the telescope (and bin-
oculars), and the compound microscope.
The main parts of the eye are the cornea,
the iris, the lens, and the retina.
Three common vision problems are
farsightedness, nearsightedness, and
astigmatism.
Two types of aberrations are spherical
aberration and chromatic aberration.
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Key Terms
lens (p. 603)
converging lens
   (p. 603)
convex lens (p. 603)
diverging lens
   (p. 603)
concave lens (p. 603)
principal axis
  (p. 604)
focal point (p. 604)
focal plane (p. 604)
focal length (p. 604)
real image (p. 605)
ray diagram (p. 606)
eyepiece (p. 611)
objective lens (p. 612)
cornea (p. 612)
iris (p. 612)
pupil (p. 612)
retina (p. 612)
farsighted (p. 614)
nearsighted (p. 615)
astigmatism (p. 615)
aberration (p. 615)
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ASSESS
Check Concepts
30 ASSESS
Check Concepts
Section 30.1
Section 30.2
(continued)
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8. What types of images are formed by diverg-
   ing lenses?
Section 30.5
1. Distinguish between a converging lens
   and a diverging lens.
2. Distinguish between the focal point and
   focal plane of a lens.
3. Distinguish between a virtual image and
   a real image.
9. Explain what is meant by saying that in
   a telescope one looks at the image of an
   image.
10. What is the function of the eyepiece in
    an astronomical telecsope?
11. What type of lenses are used in a com-
    pound microscope?
Section 30.6
12. Which instrument—a telescope, a com-
    pound microscope, or a camera—is most
    similar to the eye?
13. Why do you not normally notice a blind
    spot when you look at your surroundings?
Section 30.3
4. There are three convenient rays com-
   monly used in ray diagrams to estimate the
   position of an image. Describe these three
   rays in terms of their orientation with
   respect to the principal axis and focal
   points.
5. How many of the rays in Question 4 are
   necessary for estimating the position of
   an image?
6. Do ray diagrams apply only to converg-
   ing lenses, or to diverging lenses also?
Section 30.4
Section 30.7
14. Distinguish between farsighted and
    nearsighted vision.
15. What is astigmatism, and how can it be
    corrected?
Section 30.8
7. What types of images are formed by con-
   verging lenses?
16. Distinguish between spherical aberration
    and chromatic aberration, and cite a remedy
    for each.
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Think and Rank
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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)
17. Percy stands at different distances from a
    lens with a focal length of 30 cm. Rank the
    image distance from farthest to Percy to
    closest to Percy.
19. Here Percy is in front of a diverging lens.
    Virtual images are seen by viewing from the
    right side of the lens. For object positions A,
    B, and C, rank the sizes of the virtual images
    from largest to smallest.
Think and Explain
••••••
20. When you cover the top half of a camera
    lens, what effect does this have on the pic-
    tures taken?
(A) Object is at 10 cm.
(B) Object is at 35 cm.
(C) Object is at 60 cm.
(D)Object is at 90 cm.
18. Depending on the location of Percy rela-
    tive to the focal point of the converging lens
    (only one of the symmetrical focal points is
    shown here), the image may be real or vir-
    tual. The size of the image varies for object
    positions A, B, and C. Rank the image sizes
    from largest to smallest. (You may want to
    draw ray diagrams on a separate piece of
    paper.)
21. What will happen to the image projected
    onto a screen by a lens when you cover most
    of the lens?
22. a. What condition must exist for a converg-
       ing lens to produce a virtual image?
    b. What condition must exist for a diverging
       lens to produce a real image?
23. How could you demonstrate that an
    image was indeed a real image?
24. Why do you suppose that a magnifying
    glass has often been called a “burning glass”?
25. In terms of focal length, how far is the
    camera lens from the film or chip when very
    distant objects are being photographed?
26. Can you photograph yourself in a mir-
    ror and focus the camera on both your
    image and the mirror frame? Explain.
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30 ASSESS
(continued)
27. If you take a photograph of your image
    in a plane mirror, how many meters away
    should you set your focus if you are 2 m
    in front of the mirror?
28. Copy the three drawings in the figure.
    Then use ray diagrams to find the image of
    each arrow.
34. A whale’s eye uses hydraulics to move the
    lens of its eye closer or farther from the
    retina. When a whale dives after having had
    a look around in the air, in which direction
    should the lens be moved?
35. Focal-length variations in birds and rep-
    tiles are accomplished by eye muscles that
    change lens thickness and curvature. For
    near vision, should the lens be made thicker
    and more curved or thinner and less curved?
36. Would telescopes and microscopes mag-
    nify if light had the same speed in glass as in
    air? Explain.
37. If you have ever watched a water strider
    or other insect upon the surface of water,
    you may have noticed a large shadow cast by
    the contact point where the thin legs touch
    the water surface. Then around the shadow
    is a bright ring. What accounts for this?
29. Maps of the moon are actually upside
    down. Why is this so?
30. The real image produced by a converging
    lens is inverted. Our eyes have converging
    lenses. Does this mean the images you see
    are upside down on your retinas? Explain.
31. In which case does light undergo the greater
    change in speed—traveling in air and enter-
    ing a glass lens, or traveling in water and
    entering a glass lens?
32. In which case is refraction greater, light in
    water entering a glass lens, or light in air
    entering a glass lens?
33. From water to glass, the change in the speed
    of light is less than from air to glass. Does
    this mean a magnifying glass submerged in
    water will magnify more or less than in air?
38. What is responsible for the rainbow-
    colored fringe commonly seen at the edges
    of a spot of white light from the beam of a
    slide projector?
39. Waves overlap very little in the image of a
    pinhole camera. Does this feature contrib-
    ute to sharpness or to a blurry image?
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Activities
Activities
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40. Look at the reflection of overhead lights
    from the two surfaces of eyeglasses, and you
    will see two fascinatingly different images.
    Why are they different?
41. Note the shapes of light spots that reach
    the ground in the shade of a tree. Most of
    them are circular, or elliptical if the sun is
    low in the sky. Interestingly, the spots of
    light are images of something very special
    to all who live on Earth. Identify this special
    something.
42. Determine the magnification power of a
    lens by focusing on the lines of a ruled piece
    of paper. Count the spaces between the lines
    that fit into one magnified space, and you
    have the magnification power of the lens.
    For example, if three spaces fit into one
    magnified space, then the magnification
    power of the lens is 3. Describe how you can
    do the same with binoculars and a distant
    brick wall.
43. Make a pinhole camera, as illustrated
    in the figure. Cut out one end of a small
    cardboard box, and cover the end with
    tissue paper. Make a clean-cut pinhole at
    the other end. Aim the camera at a bright
    object in a darkened room, and you will see
    an upside-down image on the translucent
    tissue paper. In a dark, windowless room,
    if you replace the tissue paper with unex-
    posed photographic film, cover the back so
    it is light-tight, and cover the pinhole with
    a removable flap, you will be ready to take
    a picture.
Exposure times differ, depending mostly on
the kind of film and the amount of light.
Try different exposure times, starting with
about 3 seconds. Also try boxes of various
lengths. You’ll find everything in focus in
your photographs, but the pictures will not
have clear-cut, sharp outlines. The principal
difference between your pinhole camera
and a commercial one is the glass lens,
which is larger than the pinhole and there-
fore admits more light in less time.
Teaching Resources
More Problem-Solving Practice
Appendix F
CHAPTER 30
CHAPTER 30
LENSES
LENSES
• Computer Test Bank
• Chapter and Unit Tests
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