BC SCIENCE 8
CHAPTER 5: OPTICAL SYSTEMS MAKE USE OF MIRRORS AND LENSES
5.1 THE RAY MODEL OF LIGHT
To begin:
1. Start learning the vocabulary for this chapter by making flashcards or a
vocabulary sheet in the Cornell note style using the vocabulary words that are in
bold print or highlighted in the text.
2. Go to pages 68-69 in the workbook. Read and answer the questions.
3. Then read 5.1 pp. 168-175 in your text.
I. The Particle Model of Light
A. proposed by Sir Isaac Newton
B. thought that light was a stream of unimaginably small particles
that travel in a straight line until they entered the eye and were
absorbed to make an image
II. The Wave Model of Light
A. light has properties of waves
1. wavelength and frequency of the waves can explain the
different colours of light
III. The Ray Model of Light
A. useful for the study of optics (how light reflects of mirrors and
passes through lenses)
B. light is represented by straight lines or arrows that show the
direction the the light is travelling in
IV. Light and Matter
A. what you can see depends on the amount of light in a room and
the colour of the objects
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B. the type of matter that an object is made of determines the
amount of light it absorbs, reflects and/or transmits
C. transparent: describes a material that lets light pass through it
freely
1. examples: air, water, window glass
D. translucent: describes a material that most light rays can pass
through but get scattered in different directions
1. objects cannot be seen clearly through a translucent material
2. example: frosted windows
E. opaque: describes a material that does not allow light rays to
pass through; it only absorbs and/or reflects the light rays
V. Shadows
A. shadows are formed when an object blocks the light rays that
hit it
1. the closer the object is to the light source, the larger its
shadow
Make sure you can answer Reading Check on p. 171 #3-5.
VI. Light Can Be Reflected
A. If white paper reflects all the light that hits it, why isn’t it a
mirror?
B. the surface is not smooth enough so the light rays bounce off/
reflect in many random directions
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VII. The Law of Reflection
Figure 1. Light reflection from a plane mirror.
http://laser.physics.sunysb.edu/~amy/wise2000/websites/Mirror348.jpg
A. incident ray: the light ray that comes to the surface
B. reflected ray: the light ray that bounces off the surface
C. normal: the imaginary line that is at right angles to the surface
(or at right angles to the boundary between two materials) and
intersects that incident ray at the surface )or boundary)
D. angle of incidence (i): the angle between the incident ray and
the normal
E. angle of reflection (r): the angle between the reflected ray and
the normal
F. The Law of Reflection: the angle of reflection is equal to the
angle of incidence
VIII. Light Can Be Refracted
A. when light rays move from air to glass, they slow down because
the glass is denser than the air
B. angle of refraction: the angle between the refracted ray and
the normal
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1. when light passes into a denser medium, it slows down and is
refracted toward the normal
2. when light passes into a less dense medium, it speeds up and
is refracted away from the normal
IX. Refraction of Light in Water
A. refraction can make an object’s position seem to be different
from what it really is
X. Refraction of Light in Air
A. light bends as it travels through air at different temperature
1. can result in a mirage (a misleading appearance or illusion)
a. for example: on a hot summer day, it might look like there
are pools of water ahead
i. the air closer to the ground is hotter than the air
higher up
ii. light from the sky to the ground is bent upward as it
enters the less dense air
iii. this reflection of the sky looks like pools of water on
the ground
Make sure that you can answer Reading Check #1-8. You do not
have to write down your answers.
Now complete pp. 70-73 in the BC Science 8 workbook.
Then answer Check Your Understanding #1, 2, 4-6, 9 and 11.
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5.2 USING MIRRORS TO FORM IMAGES
First read and complete pp. 74 and 75 in the BC Science 8
workbook. Then read pp. 182-186 in the BC Science 8 textbook.
I. plane mirror: a flat, smooth mirror
II. Plane Mirrors
A. in a plane mirror, your image appears to be the same distance
behind the mirror as you are in front of the mirror
B. Image size and distance: an image in a mirror appears to be the
same size as the object and appear to be the same distance from
the mirror as the object
C. Image orientiation: top and bottom are the same between the
object and its mirror image but left and right are reversed
III. Concave Mirrors
A. concave mirror: a mirror that curves inward (the reflecting
surface is inside the curve)
B. parallel light rays hitting a concave mirror will reflect and meet/
converge at a single point called the focal point
C. if the object is farther away than the focal point from the
mirror, the reflected image will be small and upside down
Figure 2. A concave mirror with the object beyond the focus.
http://home.roadrunner.com/~enloephysics/mirror1.gif
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D. if the object is between the focal point and the mirror, the
reflected image will be larger than the object and right side up
Figure 3. A concave mirror with the object closer than the focus.
http://home.roadrunner.com/~enloephysics/mirror2.gif
E. Uses of concave mirrors
1. placing a light source at the focus produces an intense
focussed beam of light such as in spotlight, flashlights,
lighthouses and car headlights
2. large concave mirrors can collect light and focus it such as in
a large telescope
3. large, upright images are useful in shaving or make-up mirrors
IV. Convex Mirrors
A. convex mirrors: mirrors that curve outwards (the reflecting
surface is on the outside/bulge of the curve)
B. parallel light rays that hit a convex mirror will spread apart/
diverge after being reflected
1. they seem to come from a focal point behind the mirror
2. the image formed will be smaller than the object and upright
(right side up)
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Figure 4. The image formed using a convex mirror.
http://home.roadrunner.com/~enloephysics/mirror3.gif
C. uses of convex mirrors: security mirrors in grocery stores,
rearview and sideview mirrors on cars, mirrors in parking lots
that allow drivers to see around corners
Now make sure that you can answer Reading Check #1-6 on p.186.
Next, complete pp. 76-79 in the BC Science 8 workbook.Then
answer Check Your Understanding #1-6, 9 and 10. Note that # 9
and 10 are challenging!
5.3 USING LENSES TO FORM IMAGES
First read and answer the questions on pp. 80 and 81 in the BC
Science 8 workbook. Then read pp. 190-193 in the BC Science 8
textbook.
I. lens: a curved piece of transparent material that refracts light in
order to converge or diverge parallel light rays
II. Concave Lenses: thinner in the middle that at the edges
A. parallel light rays that pass through this type of lens will diverge
and never meet at a focal point
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B. the image will always be upright and smaller than the actual
object
C. uses of concave lenses: some types of eyeglasses, some
telescopes, often combined with other types of lenses
Figure 5. The concave lens.
http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/ray_diag_7.gif
III. Convex Lenses: thicker in the middle than at the edges
A. parallel light rays that pass through a convex lens will come
together/converge at the focal point
B. the characteristics of the image depend on how far away the
object is from the lens
1. focal length: the distance between the lens and the focal
point/focus
a. if the object is more than 2 focal lengths away from the
lens, the image will be smaller than the object and upside
down
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b. if the object is between 1 and 2 focal lengths away from
the lens, the image will be larger than the object and
upside down
c. if the object is less than one focal length away from the
lens, the image will be larger than the object and upright/
right side up
Make sure that you can answer the Reading Check #1-4 on p. 193.
Now complete pp. 82-85 in the BC Science 8 workbook. Then
answer Check Your Understanding #1-5, 8-11 on p. 197 in the
BC Science 8 textbook.
To Review the whole chapter:
1. Complete your flashcards or a vocabulary sheet in the Cornell notes
style for Ch. 4.
2. Go to pp. 198-199 in the text and answer the Chapter Review #1-6,
9-13 and 15.
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