UNIT
E
Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
(c)
2.
(a)
3.
(c)
4.
(a)
5.
(c)
6.
(c)
7.
(d)
8.
(a)
9.
10.
True
True
11.
False. Light can travel in a vacuum.
12.
False. A light ray undergoes partial reflection and transmission when it strikes a surface such as a piece
of glass.
13.
False. The centre of a lens is called the optical centre.
14.
False. A converging lens brings light rays closer together after refraction.
15.
True
16.
False. A light ray that is parallel to the principal axis is refracted to either pass through the principal focus
or in a direction that can be traced back to the principal focus.
17.
True
18.
False. Film is similar to the retina.
19.
False. An object on the secondary principal focus does not produce an image.
20.
luminous
21.
light
22.
gamma
23.
24.
converging
25.
90 o
26.
div erging
27.
28.
critical
29.
my opia
(ii)
(d)
(v)
(b)
(iii)
(e)
(iv)
(c)
(i)
30. (a)
31. (a)
transpar ent
(e)
opaque
(b)
transparent
(f)
transluce nt
(c)
translucent
opaque
(g)
transpar ent
(d)
32.
smaller, upright
focus
A converging lens is thickest in the middle, while a diverging lens is thinnest in the middle.
33. (a)
Angle of incidence is the angle between an incident ray and the normal.
(b)
Angle of refraction is the angle between a refracted ray and the normal.
(c)
Focus is the point to which incident rays travelling parallel to the principal axis of a mirror or lens
are converged after reflection (mirror) or refraction (lens), or the point from which such incident rays
appear to originate after they have been reflected or refracted.
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(d)
Magnification is the ratio of the height of an image to the height of an object or the negative ratio of
the image distance to the object distance.
(e)
A mirage is a virtual image that forms as a result of refraction and total internal reflection in Earth’s
atmosphere.
(f)
A virtual image is an image formed by light that is not arriving at or coming from the actual image
location.
WHAT DO YOU UNDERSTAND?
34. (a)
Sample answer: rock
(b)
Sample answer: window
(c)
Sample answer: amber
35. (a)
(b)
36. (a)
Sample answer: WOW
Sample answer: MAT
Electric discharge is the production of light by electric current passing through a gas, such as in a neon light.
(b)
Bioluminescence is the production of light by chemical reactions in a living thing.
(c)
Chemiluminescence is light that is a direct by-product of a chemical reaction.
37.
The word will be reversed.
38.
All electromagnetic waves travel at the speed of light in a vacuum and need no medium for transmission.
39. (a)
(b)
40. (a)
Incandescence is the emission of light due to high temperature. Fluorescence occurs when ultraviolet
light is absorbed by a material, and some of the energy is re-emitted as visible light.
In triboluminescence, the scratching, rubbing, or crushing of certain crystals causes light to be
emitted. Phosphorescence, on the other hand, occurs when a material absorbs ultraviolet light and
then re-emits visible light over a period of time.
specular: The floor could be shiny enough to produce a mirror-like image.
(b)
diffuse: If the foil is very crumpled, the tiny flat portions will reflect light in many different directions,
thus scattering the light.
(c)
diffuse: The carpet scatters light in all directions and is not shiny at all.
(d)
specular: A flat piece of foil can act like a mirror.
41.
A laser would only direct light in a single direction. To illuminate a room, light must travel in all
directions.
42.
A diverging lens or mirror cannot redirect light rays from a point on an object through a common crossing
at a point on an image and thus cannot form real images. The human brain creates the illusion that
diverging light from these lenses or mirrors comes from a single focus point and we see a virtual image.
2F
F
virtual
image
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F
2F V
F
virtual
image
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43.
Table 1 Angles of Incidence and Reflection
Description
Angle of incidence
Angle of reflection
angle between the incident ray and the normal is 38o
38o
38o
angle between the incident ray and the normal is 12 o
12o
12o
angle between the reflected ray and the flat mirror surface is 43o
47o
47o
angle between the reflected ray and the normal is 23o
23o
23o
0°
0°
the incident ray is perpendicular to the flat mirror surface
44. (a)
(b)
Each line must run from a point on the object to the corresponding point on the image and be of
equal length on either side of the mirrored surface as well as perpendicular to the mirrored surface.
The images are the same size, reversed, the same distance from the other side of the mirrored surface,
and virtual.
P
T
P
T
(a)
45. (a)
(b)
(c)
A ray from the tip of the candle flame going parallel to the principal axis will reflect through F. A ray
from the flame tip going through F will reflect parallel to the principal axis. These rays will meet at the
image of the tip of the flame. The image is larger, inverted, beyond C, and real.
(b)
A ray from either the tip of the object arrow or its tail that is going parallel to the optical axis will
reflect in alignment with F. A ray from either the tip of the object arrow or its tail that is going
toward C will reflect back upon itself. These rays must be traced back to an apparent point of origin
to locate a virtual image of either the arrow tip or its tail. The image is smaller, upright, between the
mirror and F, and virtual.
(c)
A ray from the tip of the object arrow going parallel to the principal axis will reflect through F. A ray
going in alignment with C will reflect back upon itself. These rays must be traced back to an apparent
point of origin to locate a virtual image of the arrow tip. The image is larger, upright, on the other side
of the mirror from the object, and virtual.
object
image
F
C
object
image
(a)
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F
C
(b)
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C
object
F
image
(c)
46. (a)
(b)
47. (a)
Material B has the greater index of refraction.
Light will travel more slowly in Material B.
A ray from the tip of the object arrow going parallel to the principal axis will refract through F. A ray
from the arrow tip going through O will continue unbent. Both rays will meet at the image of the tip
of the arrow. The image is larger, inverted, beyond 2F, and real.
(b)
A ray from the tip of the candle flame going parallel to the principal axis will refract through F. A ray
from the flame tip going through O will continue unbent. These two rays will meet at the image of the
tip of the flame. The image is smaller, inverted, between 2F and F, and real.
(c)
A ray from either the tip of the object arrow or its tail that is going parallel to the principal axis will
refract in alignment with F. A ray from the arrow tip or its tail that is going through O will continue
unbent. These rays must be traced back to an apparent point of origin to locate a virtual image of the
arrow tip or its tail. The image is smaller, upright, between F and the lens, and virtual.
object
2F F
F
2F
image
(a)
object
image
object 2F F
F
2F
2F
F
image
F
2F (c)
(b)
SOLVE A PROBLEM
48.
Answers will vary, but students should explain that detergents may contain fluorescent dyes that glow
slightly in daylight due to the ultraviolet light in sunshine. The clothes are not really cleaner, but they look
whiter.
49. (a)
(b)
50.
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Ultraviolet light, especially UVB, is the form of radiation from the Sun that causes skin damage.
Anything that reduces exposure to ultraviolet light helps skin to stay healthy. This includes wearing
sunblock or sunscreen, wearing clothes that cover the skin more, wearing a hat with a wide brim, and
staying indoors during the middle part of the day when the Sun’s rays are strongest.
As the cat comes very close to the mirror, her virtual image will also come close to the other side of the
mirrored surface. But the protective glass over the mirrored surface will keep her from completely reaching
her image. She could not “touch” her image because it is virtual and there are no light rays at the image
position.
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The image will be located beyond C.
51. (a)
Yes, the image is there because light rays from points on the object are passing through the
corresponding points in the image.
You could place a small screen or piece of wax paper at the image location to see it by projection.
The image is now on the other side of the mirror and virtual. You must look into the mirror with the
object in front of you to see its image.
(b)
52.
2.05 3 108 m/s
53.
1.47
54.
The index of refraction (n) for the transparent medium must be found using the formula
sin
j1/sin j2
So, 45°/sin 30° 5 1.42
Then, use the formula v 5 c/n
v
5 3.00 3 108/ 1.42
v
5 2.13 108 m/s
55.
S
Using the formula 1/do 1 1/di 5 1/f
o, 1/di 5 1/f 2 1/do
1/d
i 51/34
2 1/45
The image is located 142 cm behind the lens.
56.
The image of the tree is on the other side of the lens at a distance of 139 cm from the optical centre.
The image is larger, inverted, beyond 2F , and real.
57.
F is 13 cm from the lens.
58. (a)
(b)
59. (a)
(b)
The image is 58 cm from the lens on the same side as the sea shell. The image is larger, upright,
beyond 2F and virtual.
M 5 3.4
vir tual
f 5 28.1 cm
60.
The fruit bowl is 22 cm from the centre of the lens.
61.
M = 23.1
CREATE AND EVALUATE
62.
Student answers should focus on the low efficiency of incandescent bulbs, the better efficiency of CFL’s,
but note also that the latter pose environmental problems because of mercury, and then suggest LEDs as
the most environmentally friendly and energy efficient option.
63.
These mirrors show a wide range of view, so they can be used to help see traffic around the sharp turn.
64. (a)
(b)
The Sun provides energy to plankton in the ocean and plants on the land, providing the bases of food
chains for almost all organisms on Earth.
Students’ notices should explain that too much exposure to the Sun is a risk factor for skin cancer.
Ways that people can protect themselves from the Sun’s harmful rays include using sunscreen and
wearing a hat.
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65.
Students’ diagrams should show something similar to the diagram below. In the diagram below, light
changes speed as it moves from water to air. Light slows down as it enters a denser medium, resulting in a
change in the direction it travels. Student diagrams should show light bending toward the normal if it is
travelling into a denser medium, and light bending away from the normal if it is travelling into a less
dense medium.
n1 > n2
air
n2 1.00
water
n1 1.33
66.
Similarities
Differences
use a converging lens
a camera is focused by changing the distance between the
lens and film, but the eye focuses by changing the shape
of its lens
a smaller-than-life, inverted image is produced
the eye sees images, but cannot store them for later viewing
or printing like a camera
can focus images for different object distances
67.
Answers will vary, but students could explain that radiation can mean life-sustaining energy from the Sun;
illumination of homes and streets at night; lasers for electronics, industry, surgery and entertainment;
treatment of cancer with gamma rays; and using x-rays to image internal organs and broken bones
68. (a)
Her problem is likely presbyopia.
(b)
The diagram should show that the aunt’s eye lenses cannot flex enough to converge light rays from
nearby objects to a proper focus on the retina.
(c)
The optometrist would recommend a converging lens (a positive meniscus). This type of lens would
help the aunt’s eye lenses to converge rays more strongly.
cornea
retina
lens
A
A
A
A
positive
meniscus
69. (a)
(b)
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Converging mirrors and lenses have the same image characteristics with one exception: If an
image in a converging mirror forms on the same side as the object, the corresponding image in a
converging lens will form on the side opposite the object and vice versa.
Both diverging mirrors and lenses produce only smaller, upright, and virtual images. In diverging
mirrors, the image lies on the side opposite the object and in diverging lenses, the image lies on the
same side as the object.
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REFLECT ON YOUR LEARNING
70.
Answers will vary, but should address the loss of beneficial applications of non-visible electromagnetic
radiation, such as those in Chapter 11, Table 1, p. 466.
71.
Sample answer: If I could perceive all types of electromagnetic radiation, I would have X-ray vision.
I could also see radio waves and watch microwaves cooking my food.
72.
Answers will vary. Students are likely to comment on the prospect of an invisibility cloak being developed
because it sounds like science fiction, but may be nearing reality.
73. (a)
(b)
Students should include personal uses of mirrors and also technological uses of mirrors that affect
their lives such as vanity mirrors, dressing mirrors, rearview mirrors in cars, security mirrors, mirrored
reflectors in flashlights, dental mirrors and solar cooking.
Sample answers include eyeglasses, contacts, cameras, refracting telescopes, binoculars, microscopes,
movie projectors, and overhead projectors.
WEB CONNECTIONS
74.
The simplest reflecting telescope is the Newtonian design, first built by Isaac Newton in the later 1600s.
Early reflectors used solid metal mirrors, which gave way to silvered glass mirrors in the 19th century and
long-lasting aluminized glass mirrors in the 20th century. Catadioptric designs, which have both lenses
and mirrors, were developed in the 20th century.
75. (a)
(b)
Lasers are able to cut tissue easily in surgery and also cauterize bleeding vessels at the same time. Lasers
are also used to burn deposits out of clogged arteries and to drill teeth to treat cavities.
Cosmetic laser treatments include removal of birthmarks, tattoos, and unwanted hair.
76.
Galileo assembled basic refracting telescopes of up to about 30 power, including designs that allowed
him to see upright terrestrial images. Turning his telescopes to the heavens, he discovered moons orbiting
Jupiter; sunspots; lunar mountains and craters; and a full cycle of lunar-like phases shown by Venus.
77.
The MOST telescope has a small converging mirror, 15 cm in diameter, that casts images on a CCD
detector. Its mission includes studying sound wave–like oscillations in stars to learn about the stars’
structures and ages. Mission scientists also plan to study the atmospheres of planets orbiting other stars.
78. (a)
Two Dutch eyeglass makers, Janssen and his son, invented a basic compound microscope in 1590, a
form of which Robert Hooke used to examine cork in 1665. Modern compound microscopes have
much improved optics in which spherical and colour aberration are corrected.
(b)
An optical compound microscope uses waves of light to form images. Electrons, though, also have a
wavelike nature, and an electron microscope uses beams of electrons to form images with very high
magnification.
79. (a)
(b)
Applications of optics covered in this unit include plane mirrors (cars, personal grooming); curved
mirrors (reflectors in flashlights, headlights, and searchlights; collecting mirrors in telescopes, solar
cookers/heaters and radio dishes; security mirrors, right-hand car rearview mirrors); total internal
reflection (fibre optics-based devices, triangular prisms, retro-reflectors); and lenses (cameras,
projectors, magnifying glasses, microscopes, refracting telescopes, eyeglasses, and contacts).
Answers will vary depending on the technologies chosen by the students. Students might choose
an application such as microscopy. Students may describe how the development of microscopes
revolutionized the field of biology in the past and how microscopes continue to be critical to new
discoveries in biology.
80. (a)
From the earliest versions developed around 1900 to today, movie cameras rapidly capture still frames
(modern cameras shoot 24 frames per second) that can be played back by a projector to show action.
Technological developments during the 20th century include movies shot with synchronized sound,
colour movie photography, high speed frame capture for slow motion, and 3D cameras.
(b)
Answers will vary depending on the technologies chosen, but students should relate how a given
filming method leads to observing things in nature that would be hard to investigate in any other way.
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