Download 12.1 Answers

12.1
What Is Refraction?
OVERALL EXPECTATIONS
• demonstrate scientific investigation skills in the four areas of skills
• investigate, through inquiry, the properties of light, and predict its behaviour,
particularly with respect to reflection in plane and curved mirrors and
refraction in converging lenses
• demonstrate an understanding of various characteristics and properties of
light, particularly with respect to reflection in mirrors and reflection and
refraction in lenses.
Time
45–60 min
Vocabulary
• refraction
• angle of refraction
Skills
SPECIFIC EXPECTATIONS
Questioning
Observing
Analyzing
Scientific Investigation Skills
Equipment and Materials
• analyze the information gathered from research sources for reliability and bias
Developing Skills of Investigation and Communication
• use appropriate terminology related to light and optics
• use an inquiry process to investigate the refraction of light as it passes through
media of different refractive indices, compile data on their findings, and
analyze the data to determine if there is a trend
Understanding Basic Concepts
• explain the conditions required for partial reflection/refraction and for total
internal reflection in lenses, and describe the reflection/refraction using
labelled ray diagrams
• identify the factors, in qualitative and quantitative terms, that affect the
refraction of light as it passes from one medium to another
KEY CONCEPTS
• Light changes direction predictably as it travels through different transparent media.
• Light bends toward the normal when it slows down in a medium with a higher index
of refraction.
per group:
• beaker or other transparent
container
• stir stick
• coin
• water
Assessment Resources
Assessment Rubric 1:
Knowledge and
Understanding
Assessment Summary 1:
Knowledge and
Understanding
Other Program Resources
Skills Handbook 3. Scientific
Inquiry Skills
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
EVIDENCE OF LEARNING
Related Resources
Look for evidence that students can
Gizmo: Refraction
• use the terms refraction and angle of refraction correctly
Hecht, Eugene. Schaum’s
Outline of Optics.
McGraw-Hill, 1974.
• describe the inquiry process they used to investigate the refraction of light as it
passes through different media
• explain the conditions required for partial reflection/refraction to occur
• describe factors that cause the refraction of light as it passes from one medium to
another
Science Perspectives 10
ExamView® Test Bank
Science Perspectives 10
Teacher eSource SUITE
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website www.nelson.com
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▼
SCIENCE BACKGROUND
Speed and Refraction
• The speed of light in a vacuum is given
as 299 792 458 m/s, 300 000 000 m/s,
300 000 km/s, or 3.0 3 108 m/s.
According to modern physics, nothing
can move faster than the speed of
light in a vacuum. It is the maximum
speed for all things—matter or
non-matter—in the universe. Light
and other forms of electromagnetic
energy move at the speed of light.
Light travels more slowly through
other media. In air, light travels at
a slightly slower speed than in a
vacuum, though it is almost too small
to measure. Through water, light is
slowed considerably to about
226 000 000 m/s. Within a diamond,
light has a speed of 124 000 000 m/s.
Finally, silicon slows light down to a
speed of 75 000 000 m/s.
• Note that through a given medium the
speed of light is invariant. Light being
emitted from a moving object does
not speed up the way matter would.
For example, the speed of a ball
tossed from a moving train would be
roughly the sum of the speed of the
toss and the speed of the train. Light
doesn’t behave this way. Light stays at
the same speed no matter what the
situation. For example, light coming
from a space ship moving toward you
moves at the same speed as light from
a space ship moving away from you.
• Refraction occurs when light passes
through an object or, more precisely,
passes from one medium into another.
Needless to say, both media must
be at least partially transparent: air,
glass, water, acrylic, etc. When a light
ray changes speed, it also changes
direction. This is why refraction
occurs.
• Why does an object seem to bend in
water? The change in media as light
rays leave the water causes the rays
to bend away from the normal.
• Partial reflection and refraction occurs
when some light striking a medium
is reflected from the surface of the
medium but some of the light also
passes through the medium. When
the light passes through the medium,
it is refracted. The refracted light
illuminates the opposite side of the
surface of the medium. The result
is that a person on one side can see
objects on both sides of the surface
of the medium at the same time. This
phenomenon can be seen in water
and in mirrored sunglasses.
POSSIBLE MISCONCEPTIONS
Identify
• Students may think the term media refers only to communications media
such as radio and television.
Clarify
• Explain that media is the plural of medium. One meaning of medium is
“means of communication.” Inform students that the scientific meaning of
medium is “physical substance through which energy can be transferred.”
When students look at you, light is passing through a medium, air, to reach
their eyes.
Ask What They Think Now
• At the end of the lesson, ask students to name some of the media through
which light can pass. (Sample answers: air, water, glass)
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TEACHING NOTES
Engage
• One of the main variables influencing refraction is the speed of light in a
given medium. To introduce the concept of refraction, begin the lesson by
discussing speed. Engage the students by talking about things that move at
really high speeds. Students may bring up such things as hockey slap shots,
fast cars, and rocket ships. Ask, What is the fastest thing in the universe?
Students are likely to name light as having the greatest speed of anything,
matter or non-matter. Explain that the speed of light is 300 000 000 m/s or
300 000 km/s, which means that it could travel around Earth’s equator more
than seven times in one second.
• Encourage students to think about other properties of light. Ask, Can the
direction of that path ever change? (Yes) When might it change? (when light is
reflected off a surface)
Explore and Explain
• Begin the class with a discussion of the photo in the Chapter Opener on page
510 of the Student Book. Ask students to describe what is happening and to
discuss their own experiences with this phenomenon.
• To give students a real example of the optical illusion caused by refraction,
have students complete Try This: Exploring with Light.
T RY THIS
EXPLORING WITH LIGHT
Skills
• Observing, Analyzing
Purpose
• To explore how the passage of light through
different media affects the apparent location of an
object.
Equipment and Materials (per group): beaker or
other transparent container; stir stick; coin; water
water, they may instinctively adjust the position of
the stick. Adjusting the stick will alter the results
of the experiment, so students should be advised
to focus solely on moving the stick in the same
direction it was moving before it entered the water.
• In order to keep the stir stick immobile as they move
their head to look through the side of the beaker,
students may want to rest the hand lightly on the
edge of the beaker.
Suggested Answers
Notes
• Have students work in pairs for this activity.
• Be sure students try to touch only the edge of the
coin with the stir stick.
• Remind students to keep the stick moving in the
same direction. If they see the stick refract in the
A. No, I did not touch the outer edge of the coin with
the stick.
B. The stick went above the coin.
C. Sample answer: I missed the coin because it was not
actually in the location that it appeared to be in.
• Help students compare the definition of angle of refraction to that of angle of
reflection to note similarities and differences. The discussion should focus on the
relationship between the incident ray, the normal, and the reflected/refracted ray.
• Continue by explaining how refraction happens. Use Figure 3 on page 516 as
a basis for this discussion, as it shows a real-life example of something that is
analogous to refraction. Emphasize that this example is not exactly what takes
place in refraction of light and is only to help them grasp the concept.
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Learning Tip
Using an Analogy
Have students suggest
other analogies for
observed phenomena,
such as light reflecting off
a mirror (Sample answer: a
ball bouncing off a wall).
Reading Tip
Evaluating
Encourage students to
evaluate the main idea
of every paragraph or
section they read, even
if only briefly. Emphasize
that being able to relate
previous knowledge and
experiences to the main
idea makes it easier to
continue thinking and
learning about the material
following the main idea.
• Continue the discussion of refraction in the context of Figure 4 on page 517.
Draw a diagram on the board showing the key features of refraction shown in
Figure 4. Ask students to identify the incident ray, the angle of incidence, the
normal, the refracted ray, and the angle of refraction. Ask, How do you know that
the refracted ray is bent toward the normal? (It is smaller than the angle that would
result if the incident ray did not bend.)
• Students may need to see additional examples to fully understand the rules
for refraction. Draw a diagram on the board similar to Figure 4 showing just
the chamber and the incident ray. Ask, Where is the normal? Have a volunteer
draw the normal. Tell students that both the top medium and the chamber
are filled with air. Ask, What path will the ray take when it enters the chamber?
(straight through without bending) Have a volunteer show the path of the ray
on the board. Draw a new diagram and indicate that the top medium is now
air and the bottom one is water. Ask, What path will the ray take when it enters
the chamber? (bend toward the normal) Have a volunteer show the path of
the ray on the board. Why is the path bent toward the normal? (because water
slows the light down)
• Repeat the process, this time with the top medium containing water and
the bottom containing air. Ask, What path will the ray take when it enters
the chamber? (bend away from the normal) Have a volunteer show the path
of the ray on the board. Why is the path bent away the normal? (because air
speeds the light up)
• Relate what students have just learned to real-world objects. Bring their
attention to Figures 5 and 6 on page 517. To help them understand what is
happening, draw a diagram like the one shown below on the board. Explain
that as light rays leave the water, they bend away from the normal. This
causes them to appear as if they are originating at point Y, when they are
really originating at point X. The actual location of the object’s end is at point
X in the diagram, but the eye sees the end at point y. This change in position
explains the “bending” that takes place in refraction.
air
water
y
x
• Have students complete Try This: Examining Light in a Window (next
page). As this activity does not require any special equipment, you may wish
to assign it for students to complete at home.
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T RY THIS
EXAMINING LIGHT IN A WINDOW
Skills
• Questioning, Observing
B. Some of the light coming from me must have reflected
off the window and travelled back to my eyes.
Purpose
• Students will determine how a medium can reflect
and transmit light at the same time.
C. Sample answer: It surprised me that light can both
reflect and pass through a window simultaneously.
Notes
• If students have trouble seeing their reflections,
shining a bright light on them—not on the
window—will help.
Suggested Answers
A. The light coming from me must have travelled
through the window to reach the outside
observer’s eyes.
D. The tennis ball could bounce off the window or it
could pass through the window by breaking it. The
ball could not do both of these things at the same
time because the ball cannot be in two places at once.
E. Sample answer: The ability of light to reflect from
a window and pass through the window at the
same time suggests that light cannot just be a
stream of ordinary particles like tiny tennis balls.
However, I can imagine a spray of water both
bouncing off of and passing through a screen.
Extend and Assess
• Draw a typical diagram of refraction on the board (similar to Figure 4) without
labelling either medium. Have students copy the diagram; then ask, Which
medium is air and which is water? Label your diagram. (top: air; bottom: water)
• Repeat with the reverse situation—air on the bottom and water on top—
again without any labels. Which medium is air and which is water? Label your
diagram. (top: water, bottom: air)
• Change the situation by labelling the media (water and air) but not the
direction of the light rays. Have students draw the correct direction of light
rays for each situation. Check students’ work to assess their understanding of
the concepts in this section.
• Have students complete the Check Your Learning questions on page 519 of
the Student Book.
CHECK
Unit Task Bookmark
Encourage students to
think about whether
refracting light rays will
help their device function
as intended. If it would,
they should determine
where they want the
light to bend and in what
direction.
YOUR LEARNING
1. Refraction is the change in direction of a light beam that occurs when the light enters a new medium.
2. (a) When light enters a new medium, its speed changes causing the light to travel in a new direction. Light bends
toward the normal if its speed is slower in the new medium and away from the normal if its speed is greater in
the new medium.
(b) In order for light to be refracted, it must travel from one transparent medium into another, and light must have
a different speed in each medium.
(c) Light must have a slower speed in water than in air because light bends toward the normal when it enters
water from air.
3. (a) Medium A is air and medium B is ice. When light passes from one medium into another, its path will be closer
to the normal in the medium where light’s speed is slower, so medium B must be ice.
(b) The diagram does not show the direction in which the light is travelling, but this does not matter because the
light would follow the same path going either way.
4. (a) away from the normal
(b) toward the normal
5. Partial reflection and refraction are illustrated in Figure 11.
6. Sample answers: mirrored sunglasses, energy-saving window coatings, domes around ceiling-mounted security
cameras, security windows in store offices
7. Sample answer: One application of partial reflection and refraction is in the use of two-way mirrors that are used in
places where people on one side need to be able to see through the mirror but do not want people on the other side
to be able to see through. This is the case for situations such as police lineups, focus groups or other observations of
behaviour in which those being observed might behave differently if they could see the people who are observing them.
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DIFFERENTIATED INSTRUCTION
• All students, but particularly visual/spatial learners, may benefit from copying
a rectangle containing 6 horizontal rows to represent media. Label the outside
medium as air. Label the rows: water, air, water, glass, air, glass. Challenge
students to draw the path of a single oblique light ray through the rectangle.
A sample diagram is shown below.
air
water
air
water
glass
air
glass
air
• Acting out a model of refraction will be particularly beneficial to bodily/
kinesthetic learners, but all students will enjoy the following activity. You
will need to go to an open space such as the gym or an athletic field. Line
students up shoulder-to-shoulder, all facing in the same direction. If the
area you are in has markings such as sidelines, line the students up on one.
Have them hold metre sticks, poles, or similar items horizontally in front of
themselves in order to help them stay on the same plane. Mark a diagonal
“boundary” on the ground in front of them. One end of the boundary should
be 10 metres in front of the student at one end of the line, while the other
end of the boundary is 20 metres in front of the student at the other end of
the line. Tell students they will walk at a normal pace toward the boundary.
As soon as they cross the boundary, however, they must switch to taking baby
steps. Explain that crossing the boundary represents light passing through a
different medium, which causes light to slow down.
Math Connection
Challenge students to
calculate exactly how
many times faster light
is than sound. Use the
following values:
light 5 300 000 km/s,
sound 5 0.34 km/s.
(Light is 882 353 times as
fast as sound.)
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ENGLISH LANGUAGE LEARNERS
• Direct the attention of English learners to the word medium on page 516
of the Student Book. Write medium on the board. Ask, What is the plural
of this word? (media) Write media on the board. Then write phenomenon on
the board. Explain that this word forms a plural the same way medium does.
What do you think the plural of this word is? (phenomena) Explain that a few
English words, usually those borrowed from other languages, end with –a
in their plural forms. Challenge students to come up with other examples.
(Possible examples: criterion, datum, curriculum)
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