11.7
Images in Plane Mirrors
OVERALL EXPECTATIONS
• demonstrate scientific investigation skills in the four areas of skills
• identify and describe a variety of careers related to the fields of science
under study, and identify scientists, including Canadians, who have made
contributions to those fields
• 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
• virtual image
Skills
SPECIFIC EXPECTATIONS
Questioning
Predicting
Performing
Observing
Analyzing
Evaluating
Communicating
Scientific Investigation Skills
Equipment and Materials
• formulate scientific questions about observed relationships, ideas, problems,
and/or issues, make predictions, and/or formulate hypotheses to focus
inquiries or research
• conduct inquiries, controlling some variables, adapting or extending
procedures as required, and using standard equipment and materials safely,
accurately, and effectively, to collect observations and data
• analyze and interpret qualitative and/or quantitative data to determine
whether the evidence supports or refutes the initial prediction or hypothesis,
identifying possible sources of error, bias, or uncertainty
per group:
• two plane mirrors
• two mirror supports
• ruler
• protractor
• a die
per student:
• paper
• pencil
Career Exploration
Assessment Rubric 2:
Thinking and Investigation
Assessment Rubric 3:
Communication
Assessment Summary 2:
Thinking and Investigation
Assessment Summary 3:
Communication
• identify and describe a variety of careers related to the fields of science under
study and the education and training necessary for those careers
Developing Skills of Investigation and Communication
• use appropriate terminology related to light and optics
• use an inquiry process to investigate the laws of reflection, using plane and
curved mirrors, and draw ray diagrams to summarize their findings
• 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 the
images formed by plane and curved mirrors, with the aid of ray diagrams and
algebraic equations, where appropriate
Assessment Resources
Other Program Resources
BLM 0.0-4 Two-Column Table
Skills Handbook 3. Scientific
Inquiry Skills
Skills Handbook 7. Study
Skills
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
KEY CONCEPTS
• Images in flat mirrors are located at the point where the backward extensions of
reflected rays intersect.
EVIDENCE OF LEARNING
Look for evidence that students can
• describe and explain the characteristics of images formed by plane mirrors
• use the laws of reflection to make drawings of images formed by plane mirrors
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▼
SCIENCE BACKGROUND
Related Resources
The Uses of Mirrors
Rosner, Marc. The
Scientific American Book
of Great Science Fair
Projects. Wiley, 2008.
• A virtual image is an image to which
light does not really arrive at nor
come from. Instead, the light from
the object is reflected before it
reaches your eyes, so the light only
appears to come from the image.
The eyes receive the light rays, but
it is the brain that determines where
the image is located. An easy way
to determine whether an image is
virtual or not is to ask, Are my eyes
receiving light rays directly from the
object? If you can trace light rays
from the object directly to your eyes,
the image is real. If the light rays are
reflected before they reach your eyes,
the image is virtual. The virtual image
is located behind the mirror such that
the lines drawn from the object to the
corresponding point on the image are
perpendicular to the mirror.
Science Perspectives 10
ExamView® Test Bank
Science Perspectives 10
Teacher eSource SUITE
Upgrade
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
• Four characteristics describe the
images produced by plane mirrors: the
image is the same size as the actual
object, it is reversed, it appears behind
the mirror, and it is virtual. Every image
produced by a plane mirror will have
these characteristics. The properties of
the image produced distinguish plane
mirrors from curved mirrors. However,
the characteristics of the images are
just that; they are not characteristics or
properties of the mirrors.
• Individuals standing at different
locations observing an image in a
plane mirror would all perceive the
light rays as coming from the same
location; the location of the image
depends upon the location of the
object in front of the mirror, not the
location of the observer.
• Plane mirrors are employed in some
optical illusions or magic tricks. For
example, a simple plane mirror placed
diagonally in a box from corner
to corner will give the illusion of a
completely empty box when viewed
from a distance. In reality, the half of
the box located behind the mirror can
contain objects that will be concealed
from an audience.
POSSIBLE MISCONCEPTIONS
Identify
• Students may have the misconception that light rays actually exist “behind” a
mirror or on its surface, producing the image.
Clarify
• Light rays extending behind the mirror are depicted in this section by dashed
lines. Explain that these rays do not really exist. The brain interprets these
rays as being behind the mirror to form a virtual image.
Reading Tip
Using What You Know
Have a volunteer read the
Reading Tip on page 488
of the Student Book. Tell
students to be aware of
questions in the text as
they read through this
section, and to pause
after each question to try
to answer it using their
prior knowledge. Explain
that this technique will
help them remember and
understand what they are
reading.
800
Ask What They Think Now
• At the end of the section, ask, Do light rays extend behind plane mirrors?
(Students should note that the light rays shown behind plane mirrors in
diagrams do not really exist.)
TEACHING NOTES
Engage
• Engage students’ interest by holding a page of text in front of a plane mirror.
Have students describe the appearance of the words in the mirror. The first
characteristic students will most likely note is that the word is reversed. Ask
other questions to introduce the other characteristics of images in plane
mirrors to students. For example, ask, Does the image appear to be behind
the surface of the mirror or in front of the mirror? (behind) Is the image bigger,
smaller, or the same size as the actual object? (the same size). Explain that this
section will describe the principles that explain how the image is produced.
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Explore and Explain
• Give students some hands-on experience with images in mirrors by having
students complete the Try This: Writing Reflectively. They will learn how
reflecting an object in a plane mirror changes the way the object appears.
T RY THIS
WRITING REFLECTIVELY
Skills
• Questioning, Performing, Observing, Evaluating,
Communicating
Purpose
• Students will examine backwards writing using a
mirror.
Equipment and Materials
• per group: plane mirror; mirror supports (optional);
• per student: a sheet of paper; pencil
Notes
• Tell students that the skill of writing in a mirror
(so that what is written appears correctly in the
mirror) may need to be practised before it
becomes easy.
• Have students work in pairs for this activity.
Suggested Answers
A. The name on the paper is left-to-right reversed
when viewed without a mirror, but when viewed
in a mirror, it appears to be normally written.
B. Answers will vary, but most students will express
surprise at how difficult writing in this fashion
can be.
C. Answers will vary. Students may find that it is
easier to write “in the mirror” when using their
non-dominant hand because normal writing
motions are not so ingrained in this hand.
D. The image of an object in a plane mirror is left-toright reversed.
E. He may have wanted to keep his ideas private,
and by writing backwards, he made it difficult for
others to read his ideas and perhaps steal them.
• In the next activity, students learn about how an infinite number of images
can be created using a pair of plane mirrors. Have students complete the Try
This: Producing Images, and More Images, and More Images . . .
T RY THIS
PRODUCING IMAGES, AND MORE IMAGES, AND MORE IMAGES…
Skills
• Predicting, Observing, Analyzing
Purpose
• Students will investigate how plane mirrors at right
angles can produce multiple images.
Equipment and Materials
• per group: two plane mirrors; two mirror supports;
ruler; protractor; a die; paper
• per student: pencil
Notes
• Have students work in pairs for this activity.
• The number of images formed by two plane mirrors
set at an angle to each other can be determined
by using the following equation:
360°
Number of images 5
2 1.
angle between mirrors
Suggested Answers
C. The angle for 4 images in theory is 72o.
D. The angle for 5 images in theory is 60o.
E. Answers will vary depending on students’
predictions.
F.
Answers will vary. As the angle between the mirrors
gets smaller, the number of images increases toward
infinity. The images get so close together that it
becomes difficult to count them all. The object may
also block the view of some images.
G. (a) The multiple reflections in the mirrors make
the elevator seem to have much more
room inside.
(b)
A. There were 3 visible images.
B. Each mirror forms one image from a single reflection
of light from the object. The third image is produced
by a double reflection of light from the object.
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• Have students look at Figures 5 and 6 on page 490. Remind students that
light rays depicted with dashed lines do not actually exist. Light rays cannot
actually extend behind an opaque mirror. The rays, however, give us an easy
method to determine exactly where an image will appear.
• Ask a volunteer to summarize the numbered statements at the bottom of
page 490 of the Student Book. For statement 1, stress that there is no actual
distance from the image to the mirror, but rather a virtual distance because
the image is virtual.
• Then have students examine Figures 7 and 8 on page 491 to see how the
information in the numbered statements is applied. Make drawings of each
figure and ask volunteers to draw in the object–image lines. Have students
note that the object-image line is equally divided by the mirror. Explain that
this line is always perpendicular to the mirror’s surface.
• Ask students to recall some of the characteristics of images produced in plane
mirrors that they explored and discussed in the Engage activity. Encourage
students to employ the acronym SALT to help them remember the properties
of images. Then have students describe each property of an image produced
by a plane mirror. Explain that other types of mirrors produce images with
other properties, so this acronym will be important as they continue through
the information in this chapter.
Extend and Assess
• Review what students have learned in this section by asking questions such
as, What are the properties of images formed by plane mirrors? (the same size as
the object, reversed, located behind the mirror, and virtual)
• Discuss methods for locating images in plane mirrors, including the use of
light rays and the use of perpendicular lines.
• Have students complete the Check Your Learning questions on page 493 of
the Student Book.
CHECK
YOUR LEARNING
Suggested Answers
1. Sample answer: A virtual image is one that appears to be in a certain location but really is not.
2. Size 5 same as original; Attitude 5 upright, reversed; Location 5 1.8 meters directly behind the mirror; Type 5 virtual
3. The word looks reversed.
OPTICS
SCITPO
object
4. The image of the point source should appear to lie an equal distance
on the other side of the mirror along a line perpendicular to the
mirror.
image
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5. For all images: Size 5 same as original; Attitude 5 upright, reversed; Location 5 an equal distance on the other
side of the mirror; Type 5 virtual
A
image
L
K
K
L
A
image
image
(a)
(b)
(c)
6. (a) S 5 size, A 5 attitude, L 5 location, T 5 type
(b) Sample answer: Size is whether the image is larger, smaller, or the same size as the original object. Attitude
compares the direction in which the image points to the direction in which the object points. Location is where
you think the image is. Type is whether or not the image is virtual.
7. When, for example, a driver looks in the rear-view mirror of his car and sees an ambulance coming, the reversed
writing of the word “ambulance” on the hood is seen in the mirror as the normally written word.
8. Backwards writing is the act of writing words that are reversed. When these words are viewed in a mirror, the
reversal caused by the mirror makes the words look normal again.
9. A ray should travel from the person’s toe to the lower edge of the mirror and to the person’s eye. This shows that
the toe can be seen.
10. Sample answer: A mirror creates an image that makes it seem like another room is visible through a “window.”
This can make rooms seem much more spacious. Mirrors can also reflect light into dark rooms and brighten them.
11. (a) The mirrors lie at a 45o angle to the line of sight, one situated directly above the other and also parallel to it.
(b)
12. Sample answer: I knew that people’s brains can be tricked by optical illusions, but I never realized that the virtual
image produced by a mirror creates the illusion of things on the other side of the mirror even though nothing is
really there.
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DIFFERENTIATED INSTRUCTION
Unit Task B ookmark
Tell students that an
understanding of the
properties of images
formed by plane mirrors
is essential if they build
an optical device that
includes a plane mirror.
Have students make a
note card that described
the properties of these
images to use for review
when they begin work on
the Unit E Task: Building
an Optical Device. Ask
volunteers to share their
thoughts with the class.
Mathematics
Connections
• Visual/spatial learners should benefit from the creation of a SALT poster that
features sketches illustrating each letter of the acronym. Invite them to design
and create the poster. Students can use Figure 11 on page 492 of the Student
Book as a starting point. Display the poster in some prominent location in
the classroom for easy reference.
• Use Figures 5, 6, 7, and 8 on pages 490 and 491 to reinforce the information
about how an image is formed by a plane mirror. Verbal/linguistic learners
can describe what takes place in each figure. Bodily/kinesthetic learners can
use hand and body motions to act out the production of the image in threedimensional space. Visual/spatial learners can create a model of one of the
figures using cardboard and strings to represent light rays.
ENGLISH LANGUAGE LEARNERS
• English language learners can be encouraged to compare the effects of
reflection on characters in their native language and reflection of English
letters. Students can use BLM 0.0-4 Two-Column Table to organize characters
from their native language and English characters into two categories:
characters the are affected by reflection and characters that are not.
Have students relate the
reversal of images to
mathematical functions.
For example, for the
absolute value functions,
the line y 5 |x| acts as
a mirror into which a
graph is reflected. Other
functions have similar
properties.
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