CHAPTER
12
Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
Direct an incident light ray at the centre of the flat side of a semicircular block of a transparent material.
Draw the normal to the flat side at the point where the light ray hits and measure the angle between the
normal and the refracted ray.
normal
ray
box
measure this
angle
2.
Light travels at a slower speed in material B.
3.
The light always bends toward the normal when it slows down travelling into another medium.
4.
The material with an index of refraction of 2.30 will refract light the most because it has the highest index
of refraction of the four, meaning that it is more optically dense and causes the greatest slowdown.
5.
90o
6.
24.6o
7.
The actual position of the object is deeper than its apparent depth.
8.
If an observer is looking at an area with a very large number of raindrops, sunlight coming from behind
the observer can enter the drops, get dispersed into a spectrum, and then bounce back towards the
observer to create a visible rainbow.
9. (a)
The diagram should show the ray bending toward the normal,
then exiting the glass turning away from the normal parallel
to its original path.
(b)
When the light ray enters the glass, it slows down and is
refracted toward the normal. When the light ray leaves the glass,
it speeds up and bends away from the normal, following a path
that is parallel to its original path in air.
(c)
868
window
air
The angle of refraction cannot reach 90° because this would
result in total internal reflection, and that is not possible when
light travels into a medium with a higher index of refraction.
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WHAT DO YOU UNDERSTAND?
10. (a)
medium A
(b)
medium A
(c)
The ray will always bend toward the normal and have a smaller angle in the medium with a higher
index of refraction.
11.
Refraction would not occur if light had the same speed in air and glass because refraction is caused by a
change in speed when light passes from one medium into another.
12. (a)
(b)
Light entering a triangular prism can undergo total internal reflection and follow the same path it
would if mirrors were placed there instead.
Mirrored surfaces absorb a little of the light that falls on them whereas prisms absorb virtually no light,
thus producing brighter images. Also, mirrored surfaces deteriorate over time, but prisms do not.
13.
A rainbow is a virtual image. Dispersed light rays of different colours exit raindrops, and an observer’s eyes
and brain trace these rays backwards to form a virtual image.
14.
The air over the hot asphalt gets increasingly cooler
farther away from the asphalt, which creates a
gradual increase in the air’s index of refraction.
Light from the sky enters the warmer air over the
asphalt and, due to the lower index of refraction,
is refracted more and more until it is internally
reflected to form a virtual image of the sky on the
asphalt.
ncarbon disulfide 5
16.
natg 5
17.
nfluoride 5
18.
vveg. oil 5
19.
vflint glass 5
20.
vzircon 5
cool air
warm air
hot air
hot asphalt
image
SOLVE A PROBLEM
15.
object
8
3.00 3 10 m/s
1.84 3 108 m/s
3.00 3 108 m/s
1.47 3 108 m/s
3.00 3 108 m/s
2.10 3 108 m/s
3.00 3 108 m/s
1.47
3.00 3 108 m/s
1.65
3.00 3 108 m/s
1.92
5 1.63
5 2.04
5 1.43
5 2.04 3 108 m/s
5 1.82 3 108 m/s
5 1.56 3 108 m/s
CREATE AND EVALUATE
21. (a)
(b)
The light is reflected from wall to wall inside the fibre, traveling in straight lines between the
reflections.
Compared to copper cable, fibre-optic cable allows communications systems to run at higher speeds,
and fibre-optic signals can travel longer distances without having to be boosted. Also, fibre-optic cables
are less costly to maintain and are less affected by interference from radios, motors, and nearby cables.
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22.
23.
similarities
differences
They are both formed by the reflection and
refraction of light
Rainbows are formed by water droplets, whereas mirages are formed by
layers of air with a steadily increasing temperature toward the ground.
They are both virtual images
Rainbows are a result of dispersed colours, whereas mirages are images of
the sky or distant objects.
They both occur in the atmosphere
Rainbows often occur after storms, while mirages occur on hot, dry days.
Sample answer: My brother needs to dive at a point below the apparent position of the puck and go
deeper. When light rays from the puck exit the water surface, they are bent away from the normal. When
my brother’s eye and brain trace these rays back to an apparent point of origin, a virtual image of the puck
is formed that lies above the actual position of the puck in both position and depth.
air
water
virtual image
of puck
24. (a)
Sample answer: Science and technology lead to new products that can be beneficial to many, but may
also be used for harmful purposes. For example, lasers are used in a number of medical treatments that
help people, but laser weapons might be developed that could kill many people.
(b)
Sample answers: The military could find many uses for invisibility cloaks such as hiding soldiers or
equipment on a battlefield. A society with this technology would have a military advantage over other
societies. An invisibility cloak could also be used to protect cell phones from interference and even to
hide an unsightly industrial site or junkyard from view, which would benefit people.
(c)
Sample answer: It is a good idea because an invisibility cloak could be used by the military to help hide
people and vehicles.
REFLECT ON YOUR LEARNING
25. (a)
Sample answer: I learned that refraction is the bending of light due to a change in speed when light
moves into a new medium. This knowledge helped me to understand how light can be refracted in the
atmosphere and thus produce interesting phenomena, such as rainbows, shimmering, and mirages.
(b)
Sample answer: I always wondered what causes rainbows after storms and mirages over hot roads.
I used to think they were almost like magic, but now I know the science behind them and can explain
how they form using the laws of reflection and refraction.
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WEB CONNECTIONS
26.
Answers will vary. Students should describe the experimental apparatus and/or method in detail, focusing
on how light travels extremely fast, so some means of forcing the light to travel a great distance is needed
(as in Rømer’s observations of light travelling from Jupiter’s satellite Io to Earth) or some way to magnify
the effects of light reflecting between mirrors must be found.
27.
Double reflections of rays from the Sun inside rain drops can produce a secondary rainbow that lies
outside the primary rainbow and has its colours in a reverse order compared to the primary bow. Three
reflections inside raindrops can produce a tertiary rainbow, but it lies in the direction of the Sun, is broader
and dimmer than the primary bow, and can be hard to see.
28.
Students’ answers should focus on the idea that the front of the mirror is one piece of glass, but the back,
silvered surface is not exactly parallel to the front, plain glass surface. During the day, the mirror is tilted
so the driver sees the road in the silvered mirror. The partial reflection of light from the front of the mirror
is too dim to matter. At night, the mirror is tilted so that the road is visible through partial reflection from
the front surface, which is not as bright, so glare from headlights is reduced.
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