Download Images in Lenses

13.3
Images in Lenses
OVERALL EXPECTATIONS
Time
• demonstrate scientific investigation skills in the four areas of skills
• demonstrate an understanding of various characteristics and properties of
light, particularly with respect to reflection in mirrors and reflection and
refraction in lenses
45–60 min
Vocabulary
• emergent ray
Skills
SPECIFIC EXPECTATIONS
Scientific Investigation Skills
• 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
• draw conclusions based on inquiry results and research findings, and justify
their conclusions
Predicting
Performing
Observing
Analyzing
Equipment and Materials
per group:
• ray box
• single-slit mask
• rectangular prism
• blank sheet of paper
Assessment Resources
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
• describe the characteristics and positions of images formed by converging
lenses, with the aid of ray diagrams
• identify ways in which the properties of mirrors and lenses determine their
use in optical instruments
• identify the factors, in qualitative and quantitative terms, that affect the
refraction of light as it passes from one medium to another
KEY CONCEPTS
• A lens is a transparent object used to change the path of light.
Assessment Rubric 2:
Thinking and
Investigation
Assessment Summary 2:
Thinking and
Investigation
Other Program Resources
BLM 13.3-1 Imaging
Properties of Lenses
Skills Handbook 1. Safe
Science
Skills Handbook 3. Scientific
Inquiry Skills
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
• Parallel light rays are refracted through a focus when they pass through a converging
lens.
• Geometric optics can be used to determine the path of light rays through lenses.
Related Resources
Gizmos: Basic Prism
EVIDENCE OF LEARNING
Look for evidence that students can
• explain the three rules for imaging
• predict image characteristics for a light source at various distances from the lens
• understand how virtual images are formed in diverging lenses or, for converging
lenses, when the light source is located between the prime focal point and the lens
Hakim, Joy. The Story of
Science, Newton at the
Center. Smithsonian
Books, 2005.
Science Perspectives 10
ExamView® Test Bank
Science Perspectives 10
Teacher eSource SUITE
Upgrade
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
NEL
55308_04_ch13_p875-938 pp3.indd 887
Chapter 13 Lenses and Optical Devices
887
11/20/09 7:01:10 PM
▼
SCIENCE BACKGROUND
Prisms
are displaced sideways. The parallelism
of the rays only occurs because of the
parallelism of the prism. For a prism
of a different shape, the incident and
emergent rays would not be parallel.
• A prism is a transparent optical
device that has polished, flat surfaces
that can be used to either reflect
or refract light. The precise angles
of any prism, as well as the prism’s
composition, depend on the intended
use. Most prisms are made of glass,
and their size and thickness can vary
greatly according to their function.
The traditional geometric prism is
triangular, with its base and both sides
forming triangles. Prisms, however,
can take many geometric forms.
• There are three imaging rules for
converging lenses: 1) A ray parallel
to the principal axis is refracted
through the principal focus. 2) A
ray through the secondary principal
focus is refracted parallel to the
principal axis. 3) A ray through the
optical centre continues straight
through without being refracted.
• A prism is transparent to the
wavelengths of light it is designed to
affect. When refracting light, prisms can
redirect white light or break light into
its spectral colours. For refraction, the
various wavelengths of light are slowed
differently as they pass through a prism,
producing the colours of the spectrum.
• The rules for locating images in
diverging lenses are the same as for
converging lenses, except that the
light rays only appear to come from
the principal focus; they do not
really. Once students master the rules
for converging lenses, dealing with
diverging lenses will be easier.
• When light passes through a
rectangular prism, it is refracted upon
entering (at the air–glass boundary)
and then upon emerging (at the glass–
air boundary). The two refractions
produce emergent rays that are
parallel to the incident rays, but which
• The characteristics of the images
produced by a converging lens depend
on the location of the object relative
to the secondary principal focus.
A diverging lens always produces the
same image characteristics no matter
where the object is.
POSSIBLE MISCONCEPTIONS
Identify
• Students may presume that as you move toward a convex lens, the real image
keeps getting larger.
Clarify
• When the object is located exactly at F´, no image appears at all. Locating the
object closer than F´ results in an image that gets larger, but it is no longer a
real image. For any distance less than F´ the image is virtual.
Ask What They Think Now
• At the end of the section ask, What kind of image will you see when the object
distance is less than F´? Students should recognize that they will see a virtual
image that gets larger.
888
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 888
NEL
11/20/09 7:01:10 PM
TEACHING NOTES
Writing Tip
Engage
• On the board, draw Figure 3(a) from page 558 of the Student Book but do not
include the light rays. Ask the following questions, allowing time for students
to speculate about each response: Do you think an image will be produced by this
lens? If so, where will the image appear? (between F and 2F ) Will the image be
larger or smaller than the object? (smaller) Will the image be upright or inverted?
(inverted) After you have revealed the answers, tell students that they will learn
how to form images for both convex and concave lenses in this section.
Explore and Explain
• Have students complete Try This: Exploring the Rectangular Prism. This
activity gives students an opportunity to explore the relationship between rays
incident to and emergent from a prism. An understanding of this relationship is
necessary for students’ understanding of how to draw ray diagrams for lenses.
T RY THIS
Writing a Critical Analysis
Suggest students consider
what position they would
take in a critical analysis
of a camera with a fixed
focal length lens. Have
them write this in their
notebooks and include an
outline of the reasoning
they would use to support
their position.
EXPLORING THE RECTANGULAR PRISM
Skills
• Predicting, Performing, Observing, Analyzing
Purpose
• Students will observe the effect of a prism,
particularly its thickness, on an incident light ray.
Equipment and Materials (per group): ray box;
single-slit mask; rectangular prism; blank sheet
of paper
Student Safety
• Have students take care when handling prisms,
which may have a sharp edge if they have been
chipped during use.
• Remind students not to remove the plug from the ray
box by pulling on the cord, as it might damage the wire.
Notes
• Students may have to press down on the prism to
prevent light rays from travelling under the prism
and confusing the results.
• Have students work in pairs for this activity.
Suggested Answers
A. The emergent ray was parallel to the incident ray
but displaced sideways.
B. The sideways displacement of the emergent ray
was smaller.
C. If I had used an extremely thin rectangular
prism, the two rays would very nearly lie on a
single line.
D. The results should confirm the answer to C.
• Go over the rules for converging lenses in Figure 2 on page 557 of the
Student Book. Again, draw the lens, O, 2F´, F´, F, 2F, and the principal axis
without including any of the light rays shown in the diagram. Then have
a volunteer read the first rule: A ray parallel to the principal axis is refracted
through the principal focus, F. Draw a parallel incoming ray. Ask, What path
will it take on the other side of the lens? Show that the ray passes through F.
Repeat the process for rules 2 and 3, showing light rays that pass through
O and F´.
• Re-draw the Figure 3(a) set-up you drew for the Engage section. Use rules
1–3 to draw three light rays and show where they intersect. Have a volunteer
draw in the image. Ask, Why is the image real? (It is formed by actual light
rays.) Why is the image inverted? (The rays intersect below the principal
axis.) Why is the image smaller than the object? (The distance between the
intersecting rays and the principal axis is shorter than the distance between
the axis and the object.)
NEL
55308_04_ch13_p875-938 pp3.indd 889
Chapter 13 Lenses and Optical Devices
889
11/20/09 7:01:10 PM
Reading Tip
Making Connections
Have students locate
the three versions of
reflections in a concave
mirror shown in Figure 6 of
Section 11.9 on page 497
of the Student Book. Allow
them a few minutes to
examine the illustrations.
Ask volunteers to point out
similarities and differences
between the illustrations in
Figure 6 of Section 11.9 and
Figure 3 of this section.
Students should note
that the rays shown
passing through F for
concave mirrors and F ´
for converging lenses
are always parallel to the
principal axis after either
reflecting or refracting.
Unit Task B ookmark
Guide students in
determining how image
characteristics will come
into play in their device.
Even if students have not
decided which device to
build, they can consider
the fact that the final image
cannot be inverted if it is to
be used by humans. Also,
have students note that
where the image appears
will greatly affect the
construction of their device.
CHECK
• Go over Figures 3, 4, and 5 on pages 558 and 559 and make sure that
students understand each part, as various incident rays behave differently in
other parts of the illustration. Ask students questions such as, Is this incident
ray parallel or angled? Where is the light source now? What happens when it
emerges and why?
• As you work through the illustrations with students, ask them to note the
size of the image, its attitude or orientation, and if it is real. Virtual images
are drawn with dashed lines around them. Emphasize that the rules and
characteristics discussed so far are only for converging lenses.
• Explain to students that the rules for locating images in diverging lenses are
the same as for converging lenses, except for the fact that the light rays do not
come from the primary focus.
• Copy Figures 6 and 7 on pages 559 and 560 of the Student Book on the
board or overhead. Have students use their pencil to trace the rays in each
of the figures to get practice locating the image in a diverging lens. Use the
figures you drew on the board or overhead to demonstrate the rules for
locating the images. Discuss any issues or questions that students have. Ask
students to state the characteristics of images produced by diverging lenses.
Students should be able to state that the image is always upright, virtual, and
on the same side of the lens as the object.
Extend and Assess
• Have students restate in their own words the rules they have learned about
converging and diverging lenses. They should combine observations of the
position of the light source and the characteristics of the image produced
with the three imaging rules.
• Have students imagine that rule 1 for converging lenses is being questioned.
Ask, How could you prove that rule 1 is true? Have students suggest an
experiment to show that rule 1 is true. The experiment should involve shining
light beams parallel to the principal axis showing that they all pass through a
common point, F. Repeat this for diverging lenses.
• Have students complete BLM 13.3-1 Imaging Properties of Lenses, in which
they will complete diagrams that demonstrate object-image relationships of
lenses described in this section.
• Have students complete the Check Your Learning questions on page 561 of
the Student Book.
YOUR LEARNING
Suggested Answers
1. (a) Rays parallel to the principal axis go through F on the other side. Rays through F´ run parallel to the principal
axis. Rays through O keep going straight.
(b) For a diverging lens, the only difference is that the rays do not actually come from the principal focus; they just
appear to.
2. (a) (i) One ray from the tip of the candle flame goes parallel to the principal axis and refracts through F.
A second ray from the flame tip goes unbent through O. Both rays meet below the principal axis at the
image of the flame tip.
(ii) One ray from the tip of the object goes parallel to the principal axis and refracts through F. A second ray
from the arrow point goes unbent through O. Both rays meet above the principal axis at the image of the
arrow point.
(iii) One ray from the tip of the candle flame goes parallel to the principal axis and refracts through F.
A second ray from the flame tip goes unbent through O. These rays diverge and must be traced back
to the image of the flame tip on the same side of the principal axis as the candle.
890
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 890
NEL
11/20/09 7:01:10 PM
(iv) One ray from the object arrow point goes parallel to the principal axis and refracts aligned with F.
A second ray goes unbent through O. These rays diverge and must be traced back to the image of
the arrow point on the same side of the principal axis as the object arrow.
(b) (i) smaller than the object, inverted, located
between 2F and F, real
image
object
(ii) larger than the object, inverted, located beyond
2F, real
2F ⬘
F⬘
F
2F
object
2F ⬘
F⬘
F
2F
image
(iii) larger than the object, upright, located on same
side, virtual
2F ⬘
F⬘
image object
(iv) smaller than the object, upright, located on the
same side, virtual
F
2F
object
2F
3. A ray from the object arrow tip going parallel to the principal
axis will refract through F and pass through the image of the
arrow tip. This ray crosses the principal axis at F.
F
F⬘
image
2F ⬘
object
F
image
4. (a) and (b)
object
(i)
2F ⬘
F⬘
F
2F
image
object
image
(ii)
NEL
55308_04_ch13_p875-938 pp3.indd 891
2F ⬘
F⬘
F
2F
Chapter 13 Lenses and Optical Devices
891
11/25/09 12:36:16 AM
5. A real image is never formed because the emergent rays from a divergent lens always spread apart. A real image
can only be formed if the emergent refracted rays cross or converge. The human brain interprets diverging light
from this type of lens as if it were coming from a single focus point, creating a virtual image.
6. The size of the virtual images produced by a converging mirror changes depending on the distance of the object.
An image produced by a diverging mirror never changes in size. A converging lens produces a larger-than-life
virtual image, and a diverging lens produces a smaller-than-life virtual image.
7. If a lens produces a virtual image, it will be upright and located on the same side of the lens as the object. A real
image is produced if the orientation of the image is inverted to that of the original object.
8. (a) A converging lens—a real image is produced on the screen.
(b) The diagram should show the object (the film) below the principal axis, located between 2F´ and F´, so that an
enlarged, right side up image is produced.
movie screen
film source
2F F
F
2F
(c) The image is larger than life, inverted, beyond 2F, and real; for the image to appear right side up, the film must
be inserted in the projector upside down.
DIFFERENTIATED INSTRUCTION
Business Studies
Connections
Encourage students to
research developments
and innovations related
to lenses and how those
changes have affected
people’s lives. Have them
relate these developments
to demand in the
market and the efforts
of entrepreneurs and
established companies
to meet these demands.
For example, have them
consider the evolution of
the camera.
892
• Encourage visual/spatial students to create a poster for the class showing the
information in Table 1 on page 559 of the Student Book with diagrams, as
well as information on diverging lenses. Encourage students to refer to the
table as they go over different situations in this section and other sections of
the chapter.
• Bodily/kinesthetic learners should benefit from returning to the lens, candle,
and screen set-up of the previous section’s activity. Allow students to conduct
the same experiment as before, but this time using the illustrations and
descriptions contained in this section. Students should try to duplicate the
images and demonstrate the different movements and relocation of the light,
explaining as they do the experiments how the principles of refraction are
producing what they see.
ENGLISH LANGUAGE LEARNERS
• Pair students with widely varied comprehension, vocabulary, or fluency
strengths. Have students model reading for each other. Students can work to
define terminology in their own words and guide each other through their
reading.
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 892
NEL
11/20/09 7:01:11 PM