11.4
Time
45–60 min
Vocabulary
• light ray
• geometric optics
• incident light
• transparent
• translucent
• opaque
• image
• mirror
• reflection
• plane
• incident ray
• reflected ray
• normal
• perpendicular
• angle of incidence
• angle of reflection
Skills
The Ray Model of Light
OVERALL EXPECTATIONS
• 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
SPECIFIC EXPECTATIONS
Developing Skills of Investigation and Communication
• use appropriate terminology related to light and optics
• predict the qualitative characteristics of images formed by plane and curved
mirrors, test their predictions through inquiry, and summarize their findings
Understanding Basic Concepts
• describe, on the basis of observation, the characteristics and positions of
images formed by plane and curved mirrors, with the aid of ray diagrams and
algebraic equations, where appropriate
Observing
Evaluating
Equipment and Materials
per group:
• flashlight
• atomizer or similar spray
bottle filled with water
Literacy Resources
KEY CONCEPTS
• When light is reflected off a flat, shiny surface, the image is equal in size to the
object and the same distance from the surface.
• Images in flat mirrors are located at the point where the backward extensions of
reflected rays intersect.
EVIDENCE OF LEARNING
BLM 0.0-8 Term Box
Look for evidence that students can
Assessment Resources
• understand that light always moves in a straight line and that light rays are used to
represent the path and direction of light
Assessment Rubric 1:
Knowledge and
Understanding
Assessment Summary 1:
Knowledge and
Understanding
• explain how geometric optics uses light rays to predict how light will behave when it
strikes an object
Other Program Resources
Models of Light
BLM 11.4-1 The Terminology
of Reflection
Skills Handbook 3. Scientific
Inquiry Skills
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
• The ray model of light generally
ignores the wave nature of light
and treats light rays in much the
same way rays are treated in
Euclidean geometry—as straight
lines that extend infinitely in a single
direction.
SCIENCE BACKGROUND
waves), earthquake waves, and water
waves.
• When light strikes a material, three
things can occur. Light can be
absorbed, reflected, or refracted
(bent). With reflection, outgoing
light bounces back in more or less
the same form as incoming light.
With absorption, light energy usually
gets transformed into a new form of
energy (e.g., thermal energy). With
refraction, light slows down or speeds
up as it turns in a new direction.
▼
• Reflection does not only occur with
light. Reflection is also demonstrated
with other forms of energy, such
as sound waves (echoes occur
because of the reflection of sound
▼
784
Unit E: Light and Geometric Optics
55308_02_ch11_p765-826 pp3.indd 784
NEL
11/20/09 6:56:28 PM
• Smooth mirrors produce specular
reflection, a type of reflection that
occurs when an image is formed.
Diffuse reflection from irregular
surfaces causes energy to be reflected,
but no image is formed. Diffuse
reflection occurs more commonly than
specular reflection.
• The scientific symbol for a plane mirror
consists of a line with cross-hatching
to one side of it. The line represents
the reflective surface, while the crosshatching represents the opaque side of
the mirror.
• When a ray of light strikes a plane
mirror, the angle of incidence (the
angle between the incident ray and
the normal to the mirror at the point
of incidence) is equal to the angle
of reflection (the angle between the
reflected ray and the normal to the
mirror at the point of incidence).
Related Resources
Gizmo: Laser Reflection
Kirkland, Kyle, Ph.D. Light
and Optics. Facts on File,
2007.
Science Perspectives 10
ExamView® Test Bank
Science Perspectives 10
Teacher eSource SUITE
Upgrade
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
POSSIBLE MISCONCEPTIONS
Identify
• Students may be confused by the statements that light travels in a straight
line and that light radiates from a source in all directions.
Clarify
• Each ray of light is straight, but because light rays extend out from a
luminous object in all directions, the totality of the emitted light moves in all
directions.
Ask What They Think Now
• At the end of the section, ask, In what way does light travel? (Students should
recognize that light moves in a straight line and that light radiates from a
source in all directions.)
TEACHING NOTES
Engage
• To introduce the ray model of light and reflection, show students a hand
mirror. Ask students to describe how they think a mirror works. After several
students have shared their thoughts, explain that mirrors work due to the way
light behaves when it strikes a reflective surface. Tell students they will learn
more about the behaviour of light and reflection in the upcoming sections.
Explore and Explain
• Point out Figure 1 on page 479 of the Student Book. Provide a flashlight
to students and ask them to examine the beam of light that comes from the
flashlight. Point out that what they observe is similar to the “yes” scenario in
Figure 1.
• Have students examine the light rays in Figure 2. Explain that light rays are
a model used to show how electromagnetic radiation behaves. Help students
understand that light rays are not an actual object; they simply show the path
that light takes. It is also important that students understand that a ray is half
of a straight line (half because it only extends in one direction) and that lights
travels in a straight line. Explain that the few light rays drawn represent the
infinite number that actually come from the candle.
• Show students objects to help reinforce the terms transparent, translucent,
and opaque. Using plastic wrap (transparent), waxed paper (translucent), and
aluminum foil (opaque) can be an effective way to help students remember
each of these terms.
NEL
55308_02_ch11_p765-826 pp3.indd 785
Chapter 11 The Production and Reflection of Light
785
11/20/09 6:56:28 PM
• Have students complete Try This: Seeing the Light. This activity will give
them a chance to explore the physics of light and understand the relevance
of the ray model to the properties of light by actually “seeing” the rays. This
activity will also provide a good introduction to the reflection of light.
T RY THIS
SEEING THE LIGHT
Skills
• Observing, Evaluating
Purpose
• Students will observe the interaction of light and
matter.
Equipment and Materials (per group): flashlight;
atomizer or similar spray bottle filled with water
Notes
• Have students work in pairs for this activity.
Suggested Answers
A. No, I could not see the beam of light.
B. Sample answer: The light on the wall disappeared
and my hand became illuminated.
C. The light beam became visible after the water was
sprayed.
D. The light must reflect off particles or a surface in
order for it to be seen.
E. There are no particles in clean air large enough to
reflect light to an observer’s eyes. Atomized water,
though, provides water droplets that are large
enough to reflect light.
• Go over the material under the heading “Flat Mirrors” on page 480 of the
Student Book, paying particular attention to the vocabulary terms. After
discussing the terms, explain that the water droplets in the Try This activity
were acting as tiny mirrors, reflecting the light from the flashlight, which is
what made it possible to see the light in the air.
• Tell students that the ray model of light is used to study reflection from
mirrors. Have students examine Figure 5 on page 481, which shows
the scientific symbol for a mirror. Explain that this symbol will be used
throughout the remainder of the chapter. Reinforce the importance of
understanding and being able to interpret this symbol.
• Spend time on a discussion of the terms and geometry of light, as illustrated
in Figure 6 on page 481 of the Student Book. An understanding of this
material is essential for an understanding of the material throughout the
remainder of the unit. Ask (and answer) questions such as the following:
– What is the incident ray? (the incoming ray)
– What is the normal? (a line perpendicular to the mirror’s surface that
intersects the incident ray at the point where it hits the mirror’s surface)
– What is the angle of incidence? (the angle between the incident ray and the
normal)
– What is the reflected ray? (the outgoing ray that has been reflected)
– What is the angle of reflection? (the angle between the reflected ray and the
normal)
Distribute •BLM 11.4-1 The Terminology of Reflection. Have students complete
the BLM to reinforce their understanding of the vocabulary terms.
Extend and Assess
• Have students review all the vocabulary in the section and define the terms
using their own words. You may wish to distribute BLM 0.0-8 Term Box so
that students can record the terms and definitions in an organized manner.
Be certain students are familiar with these terms. Without an understanding
of the terms presented in this section, students will not be able to fully
understand the rest of the unit.
786
Unit E: Light and Geometric Optics
55308_02_ch11_p765-826 pp3.indd 786
NEL
11/20/09 6:56:28 PM
• To assess students’ understanding of the vocabulary in this section, consider
an oral quiz of the class. For half of the quiz, state the definition of a term
from the section and ask students to write the correct term. For the other
half, state a term from the section and ask students to write a short definition
in their own words. Go over the answers at the end of the quiz, asking
volunteers to provide answers. Discuss any discrepancies in student answers.
• Have students complete the Check Your Learning questions on page 481 of
the Student Book.
CHECK
YOUR LEARNING
Suggested Answers
1. (a) Most mirrors are made up of glass with a layer of shiny film (the reflective surface) on the back.
(b) The glass layer protects the shiny film, and the shiny film reflects light.
2. Geometric optics is the use of light rays to determine what light does when it strikes objects.
3. transparent: clean glass, clean air, apple juice, sunglasses; translucent: frosted glass, thin tissue paper;
opaque: textbook, rock
4. Plane mirrors have typically been used by people to view their physical appearance.
5. Sample answer: The normal is a line that is perpendicular to a surface (i.e., at 90°), touching the surface at the
point where a light ray strikes. The angle of incidence is the angle between the incoming light ray and the normal;
the angle of reflection is the angle between the reflected ray and the normal.
6. Sample answers: rear-view mirror in a car; scientific instruments like telescopes and microscopes; cameras
DIFFERENTIATED INSTRUCTION
• For visual/spatial learners, revisit the questions used above for examining
Figure 6. Give these students the option of answering each question with
a diagram. Students should label the diagram as the questions progress.
• Mathematical/logical learners may benefit from creating questions such as:
If the angle of incidence increased, what would happen to the angle of reflection?
(it would increase an equal amount) Have partners create challenging
questions for one another to answer.
ENGLISH LANGUAGE LEARNERS
• Use the following modified cloze sentences to assess English language
learners’ understanding of the main ideas of the section:
A ________ can be used to show the path of light. (light ray)
A(n) ________ object lets light pass through easily. (transparent)
A ________ is a shiny surface that reflects light. (mirror)
The ________ is the light ray that goes toward a mirror. (incident ray)
NEL
55308_02_ch11_p765-826 pp3.indd 787
Chapter 11 The Production and Reflection of Light
787
11/20/09 6:56:29 PM