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UNIT 2 : LIGHT AND GEOMETRIC OPTICS
Day 1 Types of Light Emissions pg 208
Luminous – produces its own light e.g. sun
Non-luminous – does not produce its own light and is visible due to reflected light
e.g. a tree
Sources of light
a.
Incandescence - light emitted from a material e.g.(___________metal) because of the high
_____________of the material
Only about __________ percent ( see pg 211 ) of the electrical energy used in an incandescent
bulb becomes light. The remaining _______percent is lost as___________.
b.
Light from Electric Discharge
Process of producing light by passing an electric current through a gas e.g. neon sign(______ colour),
mercury ( _________ colour) and lightning
c.
Fluorescent Bulb( pg 210 )
A fluorescent bulb is an electric discharge tube. Bulb contains ____________vapour along with an
inert gas, such as_____________inside of a fluorescent bulb is coated with a powdery substance
called____________. When electrical energy charges the electrodes, they emit_______________.
The electrons travel through the gas, from one electrode to the other. As the electrons travel through
the gas, they collide with atoms of mercury and excite these atoms. The excited mercury atoms
release their excess energy in the form of ___________light, which human eyes cannot see. The
energy of the ultraviolet light is absorbed by the phosphor, which emits visible light.
compact fluorescent bulb is _____percent efficient; that is, ________percent of the energy it uses is
converted into light. Compact fluorescent bulbs last much longer than incandescent bulbs and are 4-5
times more efficient.
d.
luminescence -
the emission of light by a material or an object that has not been heated; for example,
fluorescence
e.
phosphorescence - light that is emitted due to exposure of the source to _________light, and that
continues to be emitted for some time in the absence of the _________light : glow-in-the-dark
objects, clocks
f.
Chemiluminescence
-
Light that is produced by a chemical reaction without a rise in temperature - glow stick
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g.
Bioluminescence
-
h.
Triboluminescence
-
i.
-
light that is produced by a biochemical reaction in a living organism e.g firefly, bacteria, fish etc.
Watch video www.howstuffworks.com Light: Bioluminescence
Production of light from friction as result of scratching, crushing, or rubbing certain crystals e.g
wintergreen-flavoured candy
Light emitting diode (LED)
Light produced as a result of an electric current flowing in semiconductors ; no filament and does not
produced much heat e,g Christmas lights
Pg 211 (2-4)
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Review
1. What do all incandescent materials have in common to cause them to emit light?
2. What percentage of electrical energy used in an incandescent light bulb is converted to light?
3. How is the ultraviolet radiation produced in a fluorescent light transformed into visible light?
4. What is phosphorescence?
5. Why is chemiluminescence sometimes referred to as cool light?
6. What are 2 differences between LEDS and incandescent bulbs.
Did you know : If each Canadian household replaced one 60 W incandescent bulb with a 15 W CFL there would be
an energy saving of 73 million per year
Go to www.howstuffworks.com
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Deconstructed: Incandescent Light Bulbs Deconstructed: Compact Fluorescent Light Bulb
Saving Energy During The Holidays LCD Vs. Plasma
Deconstructed: Plasma TVs
Learning Check
1.
What does excited atom mean, and what happens after an atom is excited?
2.
Explain the meaning of incandescence.
3.
Use a diagram to explain how fluorescence works.
4.
Do you think living organisms should be genetically modified so they can be used for ornamental
purposes?
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Key Concept Review
1. (a) What are two examples of natural light?
(b) What are two examples of artificial light?
2. Why could light bulbs be called heat bulbs?
3. How is the light in an incandescent light bulb produced?
4. How is the light in a compact fluorescent light bulb produced?
5. Why are incandescent light bulbs being eliminated from widespread use?
6. State what percentage of electrical energy is converted to light energy in:
(a) an incandescent bulb
(b) a compact fluorescent bulb
7. What type of light is produced by a glow-inthe-dark object?
8. What are three examples of chemiluminescence?
9. What is the term used to describe the process in which light is produced by rubbing materials together?
10. (a) How does an electric discharge produce light?
(b) What is one example in nature of light produced by electric discharge?
(c) What is one example of artificial light produced by electric discharge?
11. What is a light-emitting diode?
12. (a) What does LED stand for?
(b) What are three advantages of LEDs?
13. (a) What does LCD stand for?
(b) What is a drawback of plasma displays compared to LCD displays?
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Day 2 The Nature of Light
Light is the only form of energy that can travel like a wave through empty space and through some materials. Light
behaves like a special kind of wave, called an ________________wave. __________ is defined as the distance from
one crest (or trough) to the next. Watch video www.howstuffworks.com Light: The Electromagnetic Spectrum
White Light Shone Through a Prism
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The colour ____has the longest wavelength of visible light, which is 700 nm (nm is the
symbol for nanometre, or 10−9 m). ______has the shortest wavelength of visible light, which is 400 nm.
Remember the order ROYGBIV (ROYGoesBrokeInVegas)
Lab Analyzing Light Sources
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Name ______________________________________
Figure 10.39 Diffraction grating glasses
Diffraction grating glasses (Figure 10.39) are useful for analyzing and comparing the light produced by various
sources. The glasses function much like a prism, splitting light into its spectrum of component colours.
Purpose
To analyze the light from various sources using diffraction grating glasses
Materials & Equipment
 diffraction grating glasses
 paper
 overhead projector
 pencil crayons
 various light sources
including bright white
light; red, green, and
blue LEDs; fluorescent
light; coloured and
clear, low power
incandescent bulbs
CAUTION: Do not shine bright light into anyone’s eyes. Incandescent light sources can become very
hot. Do not touch the bulbs or block air flow around them.
Procedure
1. Put on the diffraction grating glasses. To become familiar with the images produced by diffraction grating glasses,
look at the light from one of the regular lighting fixtures in the room. Record your observations. If there are multiple
images, describe how they are arranged. Record how many different colours are visible and whether the spectrum is
distinct or fuzzy.
2. Using four sheets of opaque paper, cover most of the top of an overhead projector, leaving a 2 cm × 2 cm region
uncovered. Project this onto a screen. Darken the room. The projected image should look like a bright, tiny white
dot. Observe the dot through your diffraction grating glasses.
(a) Compare what you see here with what you observed in step 1. How are your observations similar? How do they
differ?
(b) Observe the colours that are present in the spectrum. What colours are most intense?
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(c) Using pencil crayons, draw one spectrum showing the relative amounts of each colour.
3. Examine a fluorescent light using diffraction grating glasses.
(a) How does the fluorescent light spectrum differ from the lights in step 1 and step 2?
(b) Draw the spectrum.
4. Examine each of the red, green, and blue LEDs. Observe their spectra.
(a) Are any of the LEDs purely one colour with no other colours in their spectrums?
(b) Was there one colour that seemed to be present in all of the LEDs more than any other? If so, what colour was it?
(c) Draw each spectrum.
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5. Teacher will demonstrate various gases in discharge tube
Gas
Colour unaided
Line spectrum
Questions
6. (a) Decide which of the white lights you observed were the most and least pleasant to light a room with.
Explain what aspect of the light source made it pleasant or unpleasant for you.
(b) Compare the spectra of each light source, and suggest which parts of the spectra seem most responsible for
producing a pleasant or unpleasant lighting effect.
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Watch video : www.teachersdomain.org The Electromagnetic Spectrum: FRONTLINE
Name all of the categories of the electromagnetic spectrum. What is the same about the categories? What is
different?
What is a photon?
What is the relationship between wavelength and the amount of energy the wave carries?
What are some beneficial uses of electromagnetic radiation? What are some drawbacks?
Which parts of the electromagnetic spectrum were you exposed to in the past year? How about today?
Watch video www.teachersdomain.org
Infrared: More Than Your Eyes Can See
What is the difference between visible light and infrared light?
How is an infrared camera a helpful tool to humans?
What do the various colors on an infrared photograph signify?
Explain how infrared radiation contributes to Earth's heating and cooling.
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www.teachersdomain.orgThe Electromagnetic Spectrum: NASA
What is the relationship between wavelength and the amount of energy the wave carries?
What is the relationship between wavelength and frequency?
In the visible spectrum, which color of light has the most energy? Which has the least? How do the wavelengths
differ?
Which type of electromagnetic radiation can give you a sunburn? Which type can be used for radar?
Day 3 Name the electromagnetic wave for the following :
TV signals _____________________
Remote controls _________________
Cancer treatment __________________
Medical imaging ___________________
Radar ___________________________
Sunburn _________________________
Telecommunications ________________________
Physical therapy ____________________________
Rainbows ____________________________
Black lights ____________________________
Lets Review
What is Light?
Light is a form of ___________________________ radiation that can be seen by the eye.
What is Electromagnetic Radiation?
Electromagnetic radiation is a term used to describe ______________ that are created by the motion of
electrically charged particles. All forms of electromagnetic radiation travel at the same speed: 300 000 000
metres/second (3x108)m/s or 300 000 km/s). There are many different forms of electromagnetic waves including:
Xrays ultraviolet Violet light Red light microwave radio
Electromagnetic radiation can be classified according to the ____________of the waves. The wavelength of radio
waves used by radio stations can be several hundred metres long, or as short as a few metres. The wavelength of
microwaves in microwave ovens is about 12 cm. From the diagram, ____________ has the shortest wavelength.
Furthermore, different colours of light have different wavelengths. Red has a ___________ wavelength than violet
light. Our eyes cannot see electromagnetic radiation that has a longer wavelength than red (ie microwaves) and a
shorter wavelength than violet (ie xrays).
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Emission Review
There are many sources of light. The sun is the earth’s primary source of light, however many other things can
also emit light. Light is emitted from light bulbs, televisions and computer monitors, glow sticks, fireflies, LEDs,
fireworks and during stormy weather (lightning).
Match the following terms to the definitions: chemiluminescence, bioluminescence, incandescence,
fluorescence, phosphorescence, triboluminescence.
- the emission of light by a living organism through a chemical reaction ___________________________
- the emission of light by a material after being exposed to ultraviolet radiation or other types of radiation
________________________
- the emission of light through a chemical reaction the emission of light by a material that undergoes friction
and/or the emission of light that results from the breaking of certain crystals _________________
- the emission of light by a heated solid __________________________________
- the emission of light by a material while exposed to ultraviolet radiation __________________________
Key Concept Review
1. (a) Draw a wave that has a wavelength of 3 cm and an amplitude of 1 cm.
(b) Label the amplitude and the wavelength of the wave in (a).
(c) Label the crest and the trough of the wave in (a).
2. Explain the term “frequency” as it applies to a wave.
3. What is electromagnetic radiation?
4. (a) List three types of radiation of the invisible spectrum that have wavelengths longer than visible light.
(b) Name one application for each of these three types of radiation.
5. (a) List three types of radiation of the invisible spectrum that have wavelengths shorter than visible light.
(b) Name one application for each of these three types of radiation.
6. What properties of light does the wave model of light explain?
7. Identify six general categories of colour of the visible spectrum, from highest frequency to lowest frequency.
8. Compare red light with blue light.
(a) Which has the longer wavelength?
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(b) Which has the higher frequency?
9. (a) What are two ways in which radio waves and X-rays are similar?
(b) What are two ways in which radio waves and X-rays are different?
10. (a) Which poses more of a danger to human health, very long wavelength radiation or very short wavelength
radiation?
(b) Explain why.
Complete diagram below : Indicate examples of each type of radiation given the picture below.
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Willard S. Boyle
Digital cameras and camcorders are very common in our modern world but if it had not been for the
invention of the charge-coupled device (CCD), they might not exist today. You can find a CCD in a wide range of
imaging products, such as camcorders, cellphone cameras, telescopes, and imaging satellites. If you compare a
camera to a human eye, then the CCD is like the retina at the back of the eye that turns the image focussed onto
its surface into a digital picture. CCDs work by converting light, X-rays, ultraviolet rays, or infrared waves into a
pattern of electric charges on a silicon chip. The charges are then converted into an
image file, doing away with a need for film. Today, a less expensive technology replaces the CCD in most
consumer electronics, but in devices where the very best picture is needed, like astronomical telescopes, CCDs are
used The CCD was invented in 1969 at Bell Labs, a world-famous research facility, by a brilliant Canadian scientist
— Willard S. Boyle A charge-coupled device, part of the Keck telescope in Hawaii
Boyle earned a PhD in physics from McGill University in 1950. Three years later, he began working at Bell Labs in
New Jersey. Bell Labs recruited the best and brightest research scientists from all over the world. Boyle quickly
distinguished himself by finding a way to make lasers produce a continuous beam of light
instead of operating in bursts, which until then was the only way they worked. In 1969, along with a colleague,
George E. Smith, Boyle was given the task of exploring new areas of solid state physics. They invented the CCD,
and very quickly the scientific community and electronic companies showed interest. The age of digital image
processing was born.
Questions
1. Why is the CCD such an important invention?
2. Find out how CCDs are used in the Keck telescope.
Decision-Making Analysis
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Is a Plasma Television or an LCD Television Better for the Environment?
Figure 10.38 (a) Plasma screen and (b) LCD screen. Each type of screen has advantages and disadvantages.
Issue
What is on tonight? In Canada, the answer is sure to be a lot of televisions. Most Canadian homes have one or
more televisions, and unlike many small or portable electronic devices, televisions can use a considerable amount
of electrical energy. This means that by consuming electricity, televisions are significant producers of greenhouse
gases. Televisions may also contain toxic and difficult to recycle materials,
The environmental impact of a particular type of television can vary depending on how large its screen is and
how often it is used. Which kind of television is best for the environment?
Background Information
There are different types of televisions depending on what technology is used to make the display screen. Two
very common recent technologies are plasma and liquid crystal display (LCD). Each type has its advantages and
disadvantages, and there may not be just one correct answer when it comes to which is more eco-friendly.
The biggest advantage of LCD televisions may be that they last up to twice as long as other types. LCD
televisions are lighter weight and thinner, and they consume less energy than a plasma type. However, the largest
LCD screens use significantly more energy than smaller ones. The biggest disadvantage of LCD televisions may be
in their components. LCD components use both mercury and nitrogen trifluoride (NF 3), a gas that is over 10 000
times more potent a greenhouse gas than carbon dioxide. Currently, the amount of NF 3 being added to the
atmosphere is about equal to the amount of other greenhouse gases being added from operating two million cars.
Plasma televisions are often used in very large displays and are known for a sharp and detailed picture. They
have a wide viewing angle so they can be seen more easily from the side. Also, black appears darker on plasma
screens. Some plasma televisions use up to 30% less power than other plasma brands of the same screen size.
Power consumption increases greatly with screen size, more than other style displays. For example, a very large
living room plasma display may consume more than four times more energy than that of a traditional picture tube
television. The electricity bill is correspondingly higher as well. Some types of plasma screen include lead in their
components.
Analyze and Evaluate
Your task is to compare plasma versus LCD televisions in terms of which is better for the environment. The most
eco-friendly choice might be to not have a television at all, especially one with a very large screen. Complete the
following steps in your analysis.
1.
ScienceSource Update the background information given above. Look for new technologies that might be
better than plasma or LCD displays. If so, then you will need to explain why they are better. Manufacturing
processes change. For example, LCD manufacture that does not involve mercury is currently being
developed.
2.
Make a list in point form of advantages and disadvantages of each technology.
Skill Practice
3.
Make a list of ways you or your family make use of television and what features in a television you think are
important for the way you use one.
4.
Make a conclusion about whether your family wishes to use a television and, if so, what kind is best for you.
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Day 4 How light travels
Light ray –
is a __________ and ________ representing the direction and the straight line path of
light
Light Rays Reaching Your Eyes
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Ray Diagrams Show How Light Is Affected By Different Materials
Types of mediums
Classify these as transparent, transluscent or opaque : textbook _____, frosted glass ____, Single sheet of
thin tissue _________, clean sheet of glass _________, a rock ________, clean air ___________, apple juice
_______, sunglasses _______________
Shadows
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Umbra and Penumbra in a Shadow
ey Concept Review
1. What is the ray model of light?
2. Draw a simple ray diagram of light rays travelling out from a light bulb.
3. What are two properties of light that you can show using a ray diagram?
4. What three things can happen when light strikes an object?
5. Use a labelled ray diagram to show the difference between transparent, translucent,and opaque objects.
6. What determines how light rays behave when they strike an object?
7. Describe how a penumbra differs from an umbra, using the ray model of light.
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Key Concept Review
1. What two models are used to describe how light behaves?
2. What is the difference between a crest and a trough in a wave?
3. What is the resting position of a wave?
4. What is the difference between amplitude and wavelength?
5. (a) Sketch the electromagnetic spectrum, labelling seven general types of radiation.
(b) List two technological applications of each form of radiation.
6. Why does a dental technician put a lead apron over you when you are getting dental X-rays?
7. List the main categories of colour of the visible spectrum in order from the longest wavelength to the shortest
wavelength.
8. What is produced when all colours of visible light are combined?
9. Describe how light is produced in a fluorescent bulb.
10. Classify each of the following types of light according to its source.
(a) firefly
(b) lightning
(c) glow stick
11. How is the size of a shadow related to the distance of the object from the light source?
12 (a) What three terms are used to describe how light behaves when it strikes matter?
(b) Draw and label a ray diagram explaining each term.
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13. Is a glow-in-the-dark dial on a watch or clock an example of phosphorescence or fluorescence? Explain
your answer.
14. Use the wave model of light to explain the difference between infrared light and ultraviolet radiation.
15. Explain why it is not possible to increase both the frequency and the wavelength of a wave at the same time.
16. Black light (shown below) refers to any light source that produces primarily ultraviolet radiation.
(a) Provide a possible reason why it is called black light.
(b) Describe a use for black light.
17. (a) Write a sentence that describes the relationship between the energy of electromagnetic radiation and its
frequency.
(b) Write a sentence that describes the relationship between the energy of electromagnetic radiation and its
wavelength.
18. What is a possible disadvantage of using fluorescent bulbs?
19. Provide two reasons why an LED would be a preferable light source to an incandescent or fluorescent light
bulb.
20. Describe the conditions necessary to create a penumbra.
21. Give two reasons why a plasma display might be preferable to an LCD display.
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Day 5 Lab : reflection of light off a plane mirror : Inquiry(pg 230)
Using a plane mirror write on a piece of paper the word CAT as it would have to be written to appear as CAT in the
mirror. What are the characteristics of the image in a plane mirror? Try your name . Now proceed with the lab
activity. Pg 236
Plane Mirror Reflection
The reflective surface of the mirror may be at the back of the mirror or at the front of the mirror depending where
the reflective coating was applied to the glass or plastic you are using.
Purpose
To investigate the law of reflection using a plane mirror
Materials & Equipment
 ruler
 paper
 ray box or light source that can
be made into a single 1-mm wide
slit source
 protractor
 plane mirror
CAUTION: Do not shine bright light into anyone’s eyes. Incandescent light sources can become very
hot. Do not touch the bulbs or block air flow around the light bulbs.
Procedure
1. Use the ruler to draw a straight vertical line in the middle of a piece of paper. Use the protractor to create a
perpendicular normal at the approximate centre of the first line.
2. Place the mirror upright along the vertical line. Hold the mirror in place. The normal should be perpendicular
to the surface of the mirror.
3. Shine a ray of light at an acute angle to the normal so that it reflects where the normal meets the reflecting
surface. Use the ruler to trace the incident ray between the light source and the mirror. Then, trace the
reflected ray that reflects from the mirror.
4. Label the incident ray as i1. Label the reflected ray as r1 (Figure 11.22).
5. Repeat step 2 two more times with different angles. Be sure to label the successive incident and reflected
rays as i2, r2 and i3, r3.
6. Measure and record the angle between each light ray and normal.
Questions
7. Compare the results of the angles of incidence and reflection. Describe how they are related.
8. (a) Are your results exactly the same as the law of reflection? Explain.
(b) What aspects of your experimental method could make your results different from the law of reflection?
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-
plane mirror a mirror with a flat, reflective surface
Reflection is the change in direction of a wave when it reaches a surface and bounces off that surface.
________________the substance through which light travels
_______a straight line with an arrowhead that shows the direction in which light waves are travelling
____________ray a ray of light that travels from a light source toward a surface
angle of __________the angle between the incident ray and the normal in a ray diagram
_____________a line that is perpendicular to a surface where a ray of light meets the surface
_________ray a ray that begins at the point where the incident ray and the normal meet
angle of _________the angle between the reflected ray and the normal in a ray diagram
Laws of Reflection
1. The incident ray, the reflected ray, and the normal always lie on the same____
2. The angle of reflection, ∠r, is equal to the angle of incidence, ∠i. ∠r =∠i
Day 6 Drawing Ray Diagrams
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Draw the incident ray using a ruler. At the contact point where the incident ray hits the surface, draw a normal by
measuring a 90˚ angle with a protractor.
Measure the angle of incidence (i) between the incident ray and the normal. Make a mark to indicate the same
angle on the other side of the normal. This is the angle of reflection
Draw the reflected ray from the contact point through the mark using a ruler.
Label the incident ray, the reflected ray, the angle of incidence ( i), the angle of reflection (r), and the normal.
Learning Check
1. Why is the fact that light travels in a straight line critical to the technique of ray tracing?
2. Using a diagram, explain the laws of reflection. Include the following labels: normal, angle of incidence, angle of
reflection.
3. Draw a ray diagram in which the angle of incidence is 45°.
Locating an image
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_______image an image formed by rays that appear to be coming from a certain position, but are not
actually coming from this position; image does not form a visible projection on a screen
image has four characteristics
its location (closer than, farther than, or the same distance as the object to the mirror)
orientation (upright or inverted)
size (same size, larger than, or smaller than the object)
type (real image or virtual image).
SALT – Size,Attitude,Location,Type
When you see writing in a plane mirror, the writing looks like it is_________. All the images are__________, right
to left and left to right, compared with the objects. This characteristic is called a_______ _________.
Shiny smooth surfaces reflect regularly, other surfaces also reflect light but if the surface is rough the light is
reflected in all directions. We call this diffuse reflection.
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Complete diagrams below :
Pg 231( 1-6)pg 239(11-14)
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Day 7 Locating an Image in a Plane Mirror Using a Ray Diagram
Draw a line to represent a mirror. Add hatch marks to show the non-reflecting surface of the mirror. Draw a
simple object. The distance between the mirror and the object is called the object distance. Label a point at one
end of the object “A,” and label a point at the other end “B.”
Draw an incident ray from point A directly to the mirror at a 90° angle. Because this line is normal to the mirror,
the angle of incidence is zero. Therefore, the angle of reflection is also zero.
The reflected ray goes directly backward along the same line as the incident ray B
Watch video www.teachersdomain.org :Light and the Law of Reflection
What is a photon?
Ball bearings are used as models of photons. In what ways do ball bearings differ from photons?
Why are ball bearings used to describe the behavior of light?
The narrator says that all objects reflect light. Why can we see our reflected image in some objects but not in
others?
Have you ever cleaned and polished furniture or a car so that you could see your reflection? How did cleaning and
polishing do that?
Draw a diagram of a periscope (made of tubes and mirrors). Then, using arrows to represent beams of light
traveling in straight lines, show how the law of reflection lets us see objects that are not in our direct line of sight.
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Review Questions
1.
There is a special incident ray that reflects right back on itself.
a.
How would you aim this incident ray to achieve that effect?
b.
What is the angle of incidence of this incident ray?
2.
List the four characteristics of an image.
3.
Explain to a classmate why you can choose to draw any two rays from a point on an object to determine
its image point.
4.
Define the terms image distance and object distance as they apply to a reflection in a plane mirror.
5.
Follow the steps to locate the image of a small, square object placed in front of a plane mirror. State the
four characteristics of the image.
6.
Draw a ray diagram of an apple in front of a plane mirror. State the four image characteristics.
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Day 8 Concave Mirrors(pg 240) : Inquiry
In this activity, you will use a simple kitchen tablespoon as a concave mirror.
Materials : kitchen tablespoon with two shiny, reflective surfaces
Procedure
1. Hold up the inside of the spoon in front of your face.Look at the image of your face.
2. Bring the spoon as close to your face as you can and still see your image. Describe the characteristics of your
image in the spoon.
3. Slowly move the spoon away from your face. Observe any changes in your image as the spoon gets farther away.
If you can still see your image when the spoon is at arm’s length, have someone else move the spoon even farther
away. Describe any changes in the image of your face.
Questions
1. How is the image of your face on the inside of the spoon different from your image in a plane mirror?
2. Compare and contrast how lateral inversion happens in a plane mirror and a concave mirror.
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Concave (Converging) Mirrors and Ray Diagrams
3 Rules for Ray Diagrams for a CONCAVE MIRROR:
1.
2.
3.
Inquiry Activity
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Concave Mirrors
Question
How does the distance of the object from a concave mirror affect the size and orientation of the image?
Materials & Equipment
 2 optical benches
 good quality concave mirror with a predetermined
focal length
 light source, such as candle or light bulb
 metre stick with millimetres marked
 screen
Procedure
1. Copy Table 11.4 into your notes. Record the focal length of your concave mirror as supplied by your teacher
in the table title.
2. Set up the first optical bench with the concave mirror at one end and the light source at the other end. The
concave mirror should be angled slightly away from the light.
3. Light the candle, or turn on the light bulb. Darken the room. Align a second optical bench with a screen so
that the reflected image of the light strikes the screen, as shown in the diagram. It does not need to be in
focus yet. The optical benches are now aligned and should not be moved (Figure 11.25 on the next page).
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Table 11.4 Concave Mirror Focal Length: _______
Distance Object
Image
of
Distance Distance
Candle do (cm)
di (cm)
from
Mirror
3 times
the focal
length
2 times
the focal
length
1.5 times
the focal
length
Focal
length
0.5 of the
focal
length
Orientation
(upright or
inverted)
Object Height Image Height hi
ho (cm)
(cm)
Magnification
Figure 11.25 Step 3
4.
Move the candle to the distance indicated in the first row of the table in the “Distance of Candle from
Mirror” column. Write this actual distance into the table in the “Object Distance do” column that is beside it.
5.
Slowly move the screen along the length of the bench until the image of the candle flame comes into focus.
Measure the distance from the mirror to the screen. Record this distance as the image distance, di in the
table. Record the orientation of the flame in the table.
6.
Very carefully measure the size of the actual flame or bulb and the height of the image of the light. Record
these values in your chart.
7.
Repeat steps 4 to 6 for the next distance indicated in the table, until all rows of the table are complete.
Analyzing and Interpreting
8. How do you explain the results obtained when the object was placed at 0.5 of the focal length from the
mirror?
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Skill Practice
9. Complete the magnification column of the table. Show one of your calculations.
Forming Conclusions
10. Using the completed table, form a conclusion about:
(a) the magnification of the image based on the object’s distance from the mirror
(b) the orientation of the image based on the object’s distance from the mirror
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Day 9 Images in Concave Mirrors
concave mirror a mirror whose reflecting surface curves inward
__________axis on a concave mirror, the line that passes through the centre of curvature, C, of the mirror and
is normal to the centre of the mirror
The point at which the principal axis cuts the centre of the mirror is called the_______, ___.
The first ray travels from the top of the object to the mirror, parallel to the principal axis., the reflected ray will
pass through the ______ _________
a second ray from the top of the object through the focal point, then the reflected ray will be ________to the
principal axis
A third ray can be drawn through C, the centre of curvature, to the mirror.
any incident ray through C will reflect back on itself because it is directed along a normal to the mirror
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Pg 241(15,16)
Day 10 Drawing a Ray Diagram for an Object between F and C in Front of a Concave Mirror
Draw the principal axis and a curve to represent the concave mirror. Mark a focal point.
Then mark the point C so that it is twice as far from the mirror as the focal point is.
Draw the object so that the bottom is on the principal axis between the focal point and C
Draw a ray from the top of the object toward the mirror and parallel to the principal axis. Draw the reflected
ray back through the focal point.
Draw a ray from the top of the object through the focal point, continuing to the mirror. The reflected ray will
travel backward, parallel to the principal axis.
Draw a line from the top of the object toward the mirror, as though it is coming from C. The ray will not reach
the mirror in the drawing. You know that the reflected ray will travel back along the incident ray. The point
where the reflected rays meet is the top of the image. The bottom of the image is on the principal axis. Draw
the image.
An Object beyond the Centre of Curvature
Draw the principal axis and a curve to represent the concave mirror. Mark a focal point.
Then mark C so that it is twice as far from the mirror as the focal point.
Draw the object so that the bottom is on the principal axis beyond C.
Draw a ray from the top of the object toward the mirror, parallel to the principal axis. Draw the reflected ray
back, through the focal point. Draw a ray from the top of the object through the focal point, continuing to
the mirror. The reflected ray will travel backward, parallel to the principal axis.
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Draw a ray from the top of the object through C, continuing toward the mirror. Although the line does not
reach the mirror in the diagram, draw the reflected ray back along the incident ray. The point where the
reflected rays meet is the top of the image. The bottom of the image is on the principal axis. Draw the image.
Object at focal point
Object inside focal point
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Learning Check
1.
An object is between F and a concave mirror. Draw a ray diagram to show the characteristics of the
image.
2.
An object is in front of a concave mirror between F and C. Draw a ray diagram to show the characteristics
of the image.
3.
The distance from a make-up mirror to C (the radius of curvature) is 70 cm. How far from the mirror can a
person be and still see an upright, magnified image?
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4.
An object is in front of a concave mirror and beyond C. Draw a ray diagram to show the characteristics of
the image.
General Characteristics for Concave Mirror Images:
Object past the focal point:
________, _______image __________ mirror
Object at focal point:
______________________________
Object inside focal point:
_______, ___________image ___________mirror.
Here, the image distance is negative.
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Converging Mirror Ray Diagrams
Using ray diagrams, locate the image formed and describe it using the following terms:
a) upright or inverted
b) real or virtual
c) larger, smaller, or same size as object
d) outside C, at C, between C and F, inside F, behind the mirror
Object Between C and F
a)
b)
c)
d)
Object Outside C
a)
b)
c)
d)
Object at C
a)
b)
c)
d)
Object at F
a)
b)
c)
d)
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Object Inside F
a)
b)
c)
d)
Uses of Concave Mirrors
Flashlight,Telescope,Makeup mirror,Car headlights
Magnification – measure of how much larger or smaller an image is compared the object itself
Magnification = image height/object height
Or magnification = image distance/object distance
Day 12 Images in Convex Mirrors
-
a mirror whose reflecting surface curves outward
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Reflection from the Convex Surface of a Spoon
In this activity, you will use a simple kitchen tablespoon as a convex mirror.
Materials
kitchen tablespoon with two shiny, reflective surfaces
Procedure
1. Hold up the back of the spoon in front of your face.Look at the image of your face.
2. Bring the spoon as close to your face as you can and still see your image. Describe the characteristics of
your image in the spoon.
3. Slowly move the spoon away from your face. Observe any changes in your image as the spoon gets farther
away. If you can still see your image when the spoon is at arm’s length, have someone else move the spoon
farther away. Describe any changes in the image of your face.
____________________________________________________________________________
Questions
1. How is the image of your face on the back of the spoon different from your image in a plane mirror?
_________________________________________________________________________________________
_________________________________________________________________________
2. Compare and contrast how lateral inversion happens in a plane mirror and a convex mirror.
_________________________________________________________________________________________
_________________________________________________________________________
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Applications of Convex Surfaces
security mirror - image is quite distorted, but this convex security mirror allows a clerk in the store to see a
very large area.
Convex Mirrors at Border Crossings -convex mirror is attached to the end of a long handle at an angle By
moving the mirror just under the side of the vehicle, the security guard can see everything on the bottom of
the vehicle ; also passenger side mirror in a car says objects may be closer than they appear. Why
______________________________________________________
Review Questions
1.
Using a sketch, show how you would draw a ray diagram for a convex mirror.
2.
Why is the value of the focal length of a convex mirror negative?
3.
When considering the characteristics of a concave mirror, you looked at three
different cases. Why would it not be possible to consider three similar cases for a convex mirror?
4.
Convex mirrors are oft en used as security mirrors in convenience stores. Explain why.
5.
A convex mirror has a focal length of –5 cm. An object with a height of 4 cm is 3 cm from the mirror.
Calculate the image distance and the image height. Check your results by drawing a ray diagram.
6.
Imagine that Grade 7 students are looking at a spherical ornament that has a mirror-like surface.The
students exclaim how strange the image of their faces look. Explain the distortion to them.
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Complete the following :
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Key Concept Review
1. Describe the law of reflection as a relationship between the angle of incidence, the angle of reflection, and the
normal.
2. Describe the kinds of images that can be formed by plane mirrors.
3. (a) What type of mirror produces only diverging rays?
(b) What type of mirror can produce both converging and diverging rays?
4. Describe what kind of mirror you would use if you needed to view a large, spread-out area in a small mirror.
5. Compare the shapes of convex and concave mirrors. How are they similar, and how do they differ?
6. What kind of images do convex mirrors form?
7. What are three uses for convex mirrors?
8. A lighted object is placed at the focal point of a concave mirror. Describe the light rays reflecting off the mirror.
9. Describe how the positions of a mirror, incident ray, reflected ray, and normal are related.
10. How does your image in a mirror compare with looking directly at yourself?
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Day 14 Refraction of Light
the bending of light as it travels, at an angle, from a material with one refractive index to a
material with a different refractive index
-
a light ray travels from a medium in which its speed is faster (such as air) to a medium in which its speed
is slower (such as water). The refracted ray bends _____________the normal. However, in Figure 11.7,
a light ray travels from a medium in which its speed is slower
to a medium in which its speed is faster, and the refracted ray bends away
from the normal.
Refraction is the _________of light as it passes from one transparent material to another.
Lab Observing Refraction
Purpose
To observe whether the bending of light affects the way we see certain objects
Materials & Equipment
 glass of water
 pencil
 jar lid with opaque rim
 coin
Procedure
1.
Insert a pencil into the glass of water. Observe the glass from the side at various angles. Record your
observations using labelled diagrams.
2.
Place a jar lid with an opaque rim on a desk and put a coin in the middle.
3.
Keep watching the coin while you lower the height of your head until the coin just disappears from view
behind the rim of the lid (Figure11.29).
4.
Keeping your head at the same level, pour water into the lid, on top of the coin. Observe. Record your
observations using labelled diagrams.
Figure 11.29 Step 3
Questions
5.
Describe the path of light from the water to the air.
6.
Draw a ray diagram of the light rays from the coin to your eye:
(a) in step 3
(b) in step 4
7.
Compare your drawings in question 6 with those done by classmates.
(a) How are your drawings similar?
(b) How are your drawings different?
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______________ray the ray that is bent upon entering a second medium
angle of refraction the angle between the normal and a refracted ray. Light from the submerged straw
reaches your eyes and your brain projects the rays backwards in a straight line to create a virtual image in the
water. The straw tip appears to be a _____________________ depth than it really is.
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Learning Check
1. What property of light changes from one medium to another?
2. Define the term refraction.
3. Explain why light bends when it enters the water. Include a ray diagram with your explanation.
Watch video www.teachersdomain.org
Observing Refraction of Light
Explain what happens to light when it passes from one transparent material to another.
Why do you think the speed of light slows down when traveling through a transparent material?
In the lifeguard analogy, what is meant by the "fastest path" to the swimmer?
Watch video ; www.teachersdomain.org Light and Color
What is a photon?
How does the narrator explain why we see bands of color when white light passes through a prism?
What is the difference between reflection and refraction of light?
From the diagram of the light doubly refracted by the raindrop, can you predict where an observer needs to be
with respect to the Sun in order to see a rainbow?
At what times of day is it possible to see rainbows?
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-
How much a light ray refracts is determined by the extent of the change in the speed of light as it travels
from one medium to another. When light passes from one medium to the next and the change in the
speed of light becomes greater, the angle of refraction becomes ________________________.
The speed of light is 3.00 × 108 m/s in a vacuum, such as space, where there is no matter. The speed of
light is less than 3.00 × 108 m/s in any other medium. For example, the speed of light in water is 2.26 ×
108 m/s.
-
a light ray travels from a medium in which its speed is slower to a medium in which its speed is faster,
and the refracted ray bends ______from the normal. Note that reflection always occurs.
-
index of refraction the ratio of the speed of light in a __________to the speed of light in a given
medium
Here are some typical indices of refraction:
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1.
Determine the speed of light in 3 of the materials given in the table above.
2.
What is the relationship between the index of refraction and the speed of light in the given material?
3.
In what material does light travel the fastest? the slowest?
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Basic properties of refraction:
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Refraction Drill
For each diagram, draw the normal and an approximate refracted ray.
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Sample Problem: Calculating the Speed of Light in Different Media
Problem
Calculate the speed of light in fused quartz.
Solution
Look up the index of refraction for fused quartz n = 1.46
Write the equation that relates the index of refraction to the speed
of light in the medium.
Speed in the medium (v) is the unknown variable, so arrange the
equation to solve for v.
G
R
A
S
P
1.
Calculate the speed of light in flint glass.
2.
Calculate the speed of light in crown glass.
3. a.
The speed of light in a solid is 1.24 × 108 m/s. Calculate the index of refraction.
b.
Use Table 11.1 to identify the substance.
Refraction can make objects immersed in water appear broken, and can create mirages.
-
light rays from the submerged pencil tip reaches your eyes; your brain then projects the rays backwards in
a straight line to create a virtual image in the water. The virtual image is higher than the actual pencil tip
resulting in the pencil appearing bent. The pencil tip appears at _________________________ depth than
it really is.
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Problems
1.
Define the index of refraction.
2.
Calculate the speed of light in glycerol.
3.
Why must a table that lists indices of refraction of gases include the temperature and pressure of the
gases?
4.
When white light exits a prism, the light is dispersed.
a. Explain the dispersion of white light through a prism.
b. Which colour of light travels faster in glass: yellow or violet? Explain your reasoning.
5. Use the symbols n, v, and c to show why the index of refraction of any substance is always greater than 1.
6. “Light can travel across the boundary between two media that have different indices of refraction without
bending.” What is the angle of incidence for which this statement is true? Use a diagram to support your
answer.
7. Suppose that you have two blocks of glass that look very similar.You are asked to determine which block is
crown glass and which block is flint glass. Describe a method you could use to do this. What equipment would
you need?
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Day 17
-
If light enters a medium of lower index of refraction, it will be bent ______the normal. If the angle of
incidence is large enough, the angle of refraction is 90°; at larger incident angles the light will be totally
reflected.
This is called total internal reflection, and the incident angle at which the angle of refraction is 90° is
called the critical angle, C. Total internal reflection is used in some binoculars and in optical fibers.
Fibre Optics
-
uses light to transmit information along a _____________________ cable ; cable must have a small
critical angle
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In total internal reflection, light reflects completely off the inside wall of a denser medium (higher index of
refraction) rather than passing through the wall into a less dense medium (lower index of refraction).
In an optical fibre, light is passed into the end of the fibre at an angle greater than the critical angle. Because the
fibre is made of glass, which has a higher index of refraction than the surrounding medium, the light ray is
completely reflected inside the fibre.
The Mirage
-
the pool of water on a highway is a ______________________________ ; appears when light is travelling
from ____________ air into ________________ air
index of refraction for air ______________________ as the air gets warmer; as ar temp increases light bends
more ______________________ the normal ; total internal reflection occurs in the lowest hottest air mass ;
now travels to colder layer and is refracted ____________________________ the normal.
The pool of water you see is a virtual image of the _____________________ on the highway.
Shimmering
-
is caused by light travelling at slighlt different speeds through air layers of different temperatures
at night air just above the lake is much _____________________ than air farther away
as the moonlight passes through the coldest air layer light travels ____________________ thus bends
_____________________________ the normal
as ligh enters the warmer layer its speed ____________________________ and light rays bends
_____________________________ the normal; eventually total internal reflection occurs in the lowest warm
air layer ; thus multiple virtual images of the moon.
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Refraction of Light Demonstration : www.teachersdomain.org
One of the most well-known properties of light is c, the speed of light in a vacuum (approximately 300,000 km/s).
However, the speed of light is slower when traveling through a transparent material. For example, the speed of
light traveling through glass is about two-thirds its speed in a vacuum. Depending on the material, the speed of
light will vary. This occurs because the light is absorbed and reemitted by the electrons in the material, causing a
delay. This slowing can be described by the "index of refraction," defined as the ratio of the speed of light in a
vacuum divided by the speed of light through the material; the higher its index of refraction, the slower the speed
of light will be when traveling through that material. When light crosses the boundary between two transparent
materials that have different indices of refraction (such as air and glass), it may also undergo a change in
direction. If the light approaches the boundary at an angle not along the normal line (perpendicular to the
boundary), the change in speed causes it to bend. This bending due to the change in speed is called refraction. If
the light enters into a material with a higher index of refraction, it bends towards the normal line as it slows down
in the new material. If it enters into a material with a lower index of refraction, it bends away from the normal line
as it speeds up in the new material.The refraction of light as it passes from one material to another is the
foundation for many optical devices, including magnifying glasses, eyeglasses, microscopes, and cameras. These
devices control the path of light through the use of lenses—transparent objects, usually made from glass or
plastic, that are specially shaped and designed to refract light in specific ways. There are two basic types of
lenses: converging and diverging. When parallel rays of light pass through a converging lens, they meet at a
common point. Conversely, when parallel rays of light pass through a diverging lens, they spread apart. In a
typical human eye, light from an object enters the eye and passes through a lens that focuses the light on the
retina. However, for some people, light does not focus on the retina and they have trouble seeing images clearly.
A nearsighted eye focuses the image in front of the retina; eyeglasses made with diverging lenses correct for
nearsightedness by diverging the light just enough so that the image comes into focus on the retina instead of in
front of it. Alternatively, a farsighted eye has the image coming into focus behind the retina; eyeglasses made with
converging lenses correct for farsightedness by converging the light and moving the focused image forward and
onto the retina.


According to your observations, what happens to the beam of light when it hits the rectangular glass
prism? When it exits?
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
How does the direction of light before it hits the rectangular prism compare to its direction after it exits?
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________

Why do you think the rays bend after entering the lens? Why do you think they bend after leaving the
lens?
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________

How do the shapes of these transparent objects affect light passing through them?
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________

Use a ray diagram to explain your observations. How might you use lenses in practical applications?
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
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Watch video www.teachersdomain.org
Laser Waterfall
Is the path of the laser light a curve?
If not, how does it follow the path of the water?
What do you think happens to the laser beam when all the water has flowed out of the tank?
What is total internal reflection? Can you think of some examples where total internal reflection is useful?
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Day 18
lens a transparent object with at least one curved side that causes light to refract
converging lens a lens that brings parallel light rays toward a common point
Converge means “to bring together.” Converging lenses bring parallel light rays toward a common point
When rays are incident on the surface on the left side of the lens, they move from a _______medium to a
_______ medium. Thus, the rays refract ________the normals, causing the rays to ______slightly. When the
light rays leave the second surface of the lens, they move from a _______medium to a ________medium, and
refract _________from the normals
Diverging Lenses
diverging lens a lens that spreads parallel light rays away from a common point
A good example of a diverging lens is a lens that is concave on both sides, or biconcave.
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Watch video www.teachersdomain.org Geometric Optics
Did you notice that the image of the object on the opposite side of the lens from the actual object was upside
down? Why is this so?
Why do you think increasing the curvature radius of the lens changes the location of the image?
How do you think a change in the refractive index of the lens changes the path of light rays through the lens?
What would happen to the image of the object if the top half of the lens were covered up? (Hint: try making the
lens larger and smaller in diameter)
Use the interactive activity to explain how magnifying lenses and eyeglasses work.
Learning Check
1.
What properties of a piece of glass or plastic make it a lens?
2.
Compare the shapes of converging and diverging lenses .
a.
What characteristic makes one lens converging and another diverging?
b.
Make a sketch of a converging lens and of a diverging lens. Give both lenses one plane side.
3.
Sketch a lens with one convex side and one plane side. Show how two parallel rays would refract as they
pass through this lens.
4.
Depending on the type of vision correction a person needs,contact lenses can be converging or diverging.
However, each of the two sides must have a specific shape because the lens must
fit on the surface of the eye. What must be the shape—convex,concave, or plane—of the inside of a
contact lens? Explain.
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Focal Point and Focal Length of Lenses
The principal axis of a lens is a straight line that passes through the centre of the lens, normal to both
surfaces of the lens, as with mirrors. When rays that are parallel to the principal axis pass through a
converging lens, the rays intersect at a point. As with a concave mirror, this point is called the focal point ( F)
After parallel rays pass through a diverging lens, the rays diverge. Only by tracing the rays backward do we
see that they converge to a point. This point is a virtual focus. Because light can pass through a lens from
either side, there are actually two focal points for a lens. These two focal points are the same distance from
the centre of the lens. The distance from the centre of the lens to the focal point is the focal length ( f ).
Day 19
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Ray diagrams for a converging lens
Diagram 1
do > 2f
Object
2f
f
f
2f
Real image
smaller than object
Image is inverted
di is positive and between f and 2f
Ray diagrams for a converging lens
Diagram 2
do = 2f
Object
2f
f
Real image
Same size as object
Image is inverted
di is positive and at 2f
f
2f
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Ray diagrams for a converging lens
Diagram 3
do between f and 2f
Object
f
2f
f
2f
Real image
larger than object
Image is inverted
di is positive and greater than 2f
Ray diagrams for a converging lens
Diagram 4
do = f
Object
2f
f
f
2f
Parallel rays therefore no image is formed
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Ray diagrams for a converging lens
Diagram 5
do < f
Object
2f
virtual image
f
f
2f
larger than object
Image is upright
di is negative
Ray diagram for a diverging lens
Diagram 6
do at any distance
2f
f
f
virtual image
smaller than object
Image is upright
di is negative
2f
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Day 20
Ray Tracing for Converging lens
-
Ray 1 – initially parallel to principal axis.
Ray 2 - passes through the left focal point of the lens.
Ray 3 - passes through the centre of the lens.
Learning Check
For each situation below, draw a ray diagram and describe the four characteristics of the image.
1. An object 1.5 cm high is placed 4 cm in front of a converging lens with a focal length of 3 cm.
2. An object 1 cm high is placed 5 cm from a converging lens with a focal length of 2 cm.
3. An object 1 cm high is placed 4 cm in front of a diverging lens with a focal length of 3 cm.
4. An object 1 cm high is placed 5 cm in front of a diverging lens with a focal length of 2 cm.
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The Thin Lens and Magnification Equations
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Practice Problem
An object 8.5 cm high is placed 28 cm from a converging lens. The focal length of the lens is 12 cm.
a. Calculate the image distance, di.
b. Calculate the image height, hi.
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Independent Research
Analyse a technological device or procedure related to human perception of light (e.g., eyeglasses, contact lenses,
infrared or low light vision sensors, laser surgery), and evaluate its effectiveness
Laser surgery corrects vision by surgically reshaping the cornea to correct refractive defects in the eye. While the
procedure is effective in most cases, it poses risks and can in some cases lead to poor night vision.
Questions:
How do anti-glare night vision glasses help people who have difficulty driving at night?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
How do eyeglasses with colour filters help people with dyslexia to read?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
Questions about Laser Eye Surgery
1. What common vision problems can be corrected using laser eye surgery?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
2. Identify the risks and benefits associated with these surgical procedures.
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
3. What type of laser is used in laser eye surgery?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
4. Laser vision correction surgery is advertised in the media (television, radio, etc.). Describe the effects that
media promotion of the surgery may have.
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
5. What do the letters LASIK stand for? What do the letters PRK stand for?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
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6.
What kinds of vision problems can be corrected by LASIK surgery? By PRK surgery?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
7.
Who should NOT have laser eye surgery?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
8.
Suppose you have myopia. Explain why you would, or would not, choose to have laser eye surgery in
order to correct your vision problem. Use information from your Internet research to support your
position.
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
9. Discuss the question, “Is laser vision correction surgery safe?” Consider the social, technological, and economic
factors that may affect your position.
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
10. Suppose you had vision problems that could be corrected by laser surgery. How would you decide whether to
have the surgery? What would be your main concerns and questions?
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
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Key Concept Review
1. (a) What type of lens produces a real image?
(b) What type of lens produces a virtual image?
2. A converging lens produces a real image 10 cm from the lens when the object is placed 30 cm from the lens.
(a) What is the focal length of the lens?
(b) What is the magnification of the lens?
3. An object is placed at each of the following distances from a converging lens. For each location, draw a ray
diagram and state the properties and location of the image. (Hint: Choose a convenient value for f.)
(a) 2.5 f
(b) 1.5 f
(c) 0.75 f
4. Suggest one use for each lens set-up in question 3.
5. What is one use for a diverging lens?
6. An object 1.2 cm high is placed 4.0 cm from a converging lens that has a focal length of 3.0 cm.
(a) What is the location of the image?
(b) What is the size of the image?
7. A converging lens is placed 12 cm from a wall chart. The focal length of the lens is 15 cm.
(a) What is the location of the image?
(b) What is the magnification?
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8. A photographer uses his camera to view some deer in a field. If the image of the deer is produced 120.14
mm from a convex lens that has a focal length of 120 mm, how far away are the deer?
9. At what distance from a convex lens must an object be placed so that the image is the same distance from the
lens?
10. A student examines a ladybug using a magnifying glass with focal length of 5.0 cm. He holds the magnifying
glass 3.5 cm above the ladybug. What is the magnification?
11. A photographer uses a telephoto lens to take a photograph of a 50-m high building that is 1000 m away. The
image on the negative is 2.0 cm high. What is the focal length of the lens?
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Review
1.
When an object is between a converging lens and the focal point of the lens, the three rays appear to
diverge. Why, then, is the lens considered to be a converging lens?
2.
Assume that an image is real, inverted, larger than the object, and farther from the lens than the object.
a. What type of lens is forming the image?
b. Where is the object located relative to the lens?
3.
An object 5.50 cm high is placed 100 cm from a converging lens that has a focal length of 40.0 cm.
Calculate the image distance and the image height.
4.
Solve the following problem by using both a ray diagram and algebraic equations. An object that is 3.0 cm
high is placed 14 cm from a converging lens that has a focal length of 8.0 cm.
Calculate the distance of the image and the image height.
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Research
Analyse a technological device that uses the properties of light (e.g., microscope, retro-reflector, solar oven,
camera), and explain how it has enhanced society
Sample issue: Cameras can produce a range of optical effects, from highly detailed and realistic to manipulated
and abstract. Photographic images are used for a wide range of purposes that benefit society, including in the
areas of culture, education, security, policing, entertainment, and the environment. However, the widespread use
of cameras raises privacy concerns.
Questions: How do vision sensors help the Canadian Food Inspection Agency improve food safety?
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How are photonics used in the early diagnosis of diseases such as cancer?
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How have optical fibres enhanced our ability to communicate information? How do all of these technologies benefit
society?
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How are outdoor lights such as street or stadium lights designed to limit light pollution in surrounding areas?
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watch video www.teachersdomain.org : Geometric Optics
When light travels across the boundary between two transparent materials, it is _________________—in other
words, it _______________. A ____________, a transparent object that is shaped to refract light in specific ways,
causes light rays to either converge or diverge after passing through it. In general, a converging lens is made with
_____________(outward-curving) surfaces, while a diverging lens is made with _________________(inwardcurving) surfaces.
With a converging lens, rays of light entering the lens parallel to the principal axis (the line that passes through
the center of the lens) are refracted towards the axis and converge at a common point on the axis known as
the__________________. The radius of curvature of the lens and the _______________index of the lens material
determine the focal length (the distance from the lens to the focal point). There are two focal points, one located
on each side of the lens.
The behavior of light passing through a converging lens follows certain rules. For example, if the incident
(incoming) ray travels through the center of the lens, the ray does not undergo refraction and continues in the
same direction. If the incident ray enters the lens parallel to the principal axis, the refracted ray passes through
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the focal point on the opposite side. If the incident ray passes through the focal point before entering the lens,
the refracted ray travels parallel to the axis.
At the point where the refracted rays intersect, an image is formed. Converging lenses produce both real and
virtual images. A real image forms when the refracted rays intersect after passing through the lens; a screen
placed at the plane of convergence will show an inverted image. The closer the object is to the lens (but still
farther away than the focal point), the larger the image is and the farther it is from the lens.
A virtual image is formed if the object is located at a distance less than one focal length from the front of the lens.
When this is the case, the light diverges after refraction. The virtual image appears upright, in front of the lens,
and at the location where the refracted rays would meet if they were traced backwards. To an observer, light
appears to come from the location of the virtual image, but it is not real; a screen placed at the plane of apparent
convergence would not show an image. The more distant the object is from the lens (but closer than the focal
point), the larger the virtual image is and the farther it is from the lens.
Another variable that affects how much light is captured and refracted when an image is formed is diameter—the
larger the diameter of the lens, the more light passes through it and the brighter the image.

Did you notice that the image of the object on the opposite side of the lens from the actual object was
upside down? Why is this so?
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
Why do you think increasing the curvature radius of the lens changes the location of the image?
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How do you think a change in the refractive index of the lens changes the path of light rays through the
lens?
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
What would happen to the image of the object if the top half of the lens were covered up? (Hint: try
making the lens larger and smaller in diameter)
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
Use the interactive activity to explain how magnifying lenses and eyeglasses work.
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Lens Applications
Camera
- uses __________________________ lens
- Object placed greater than 2F from the lens.
- Image is real, inverted and smaller than object.
Simple Magnifier
- Object placed between the lens and F.
Image is virtual, correct way up and larger than the object.
Projector
- Object placed between F and 2F from the lens.
- Image is real, inverted and larger than the object.
Compound microscope
- 2 converging lenses ; produces 2 enlarged inverted images one real and one virtual which you see
- complete the diagram on the right
___
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The Refracting Telescope
- same principle as compound microscope ; produces 2 images you see the larger virtual image
Unit 2 Review
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. The electromagnetic spectrum contains visible light as well as many other forms of energy. Which of the following
statements about the electromagnetic spectrum is true?
a. Gamma rays have the longest wavelength on the electromagnetic spectrum.
b. Ultraviolet waves have just slightly less energy than visible light.
c. Radio waves have the longest wavelength on the electromagnetic spectrum.
d. Infrared waves are used in radar speed measurement.
____
2. Which type of artificial light is produced by a chemical reaction without any increase in temperature, is sometimes
called a “cool light,” and is used in glow sticks?
a. phosphorescent
c. incandescent
b. fluorescent
d. chemiluminescent
____
3. Incandescent light bulbs are very inefficient. They use only this much of the electricity passing through them to
produce light.
a. 95%
c. 20%
b. 10%
d. 5%
____
4. What type of material absorbs and reflects light, but does not transmit any light?
a. shadow
c. translucent
b. transparent
d. opaque
____
5. Which of the plane mirrors would show the correct path of light?
a. III
b. I
c. II
d. IV
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____
6. What image is formed on a concave mirror if the object is between one and two focal lengths from the mirror?
a. a virtual, upright image that is larger than the object
b. a real, inverted image that is smaller than the object
c. No image is formed.
d. a real, inverted image that is larger than the object
____
7. What type of image do all convex mirrors create?
a. No image is formed.
b. a real, inverted image that is larger than the object
c. a virtual, upright image that is smaller than the object
d. a real, inverted image that is smaller than the object
____
8. Which of the following occurs when light passes from air into a pool of water?
a. The light is refracted because of the particle interference at the air–water boundary.
b. The light is refracted because light travels slower in air than in water.
c. The light passes into the water with no change to its direction or speed.
d. The light is refracted because light travels slower in water than in air.
____
9.
8
what is the refractive index of silicon?
a. 4
b. 40
m/s. If the speed of light passing through silicon is 7.5
7
m/s,
c. 2.5
d. 25
____ 10. What happens when light moves from a medium with a high refractive index into a medium with a lower refractive
a.
b.
c.
d.
The
The
The
The
ray
ray
ray
ray
of
of
of
of
light
light
light
light
speeds up and bends towards the normal.
speeds up and bends away from the normal.
continues on the exact same path.
continues on the exact same path, but at a faster speed.
____ 11. What technology uses the concept of total internal reflection for high-speed data transmission?
a. fibre optic cable
c. 3G mobile phone networks
b. microwave transmission towers
d. semiconductor coaxial cable
____ 12. What is true of the image produced by a concave lens?
a. The image is always smaller than the object, and inverted.
b. The image is always larger than the object, and inverted.
c. The image is always smaller than the object, and upright.
d. The image is always larger than the object, and upright.
____ 13. Because the light rays never meet, which of the following statements about the images produced by concave
lenses is true?
a. Concave lenses produce both real and virtual images.
b. Concave lenses produce no image.
c. Concave lenses produce only a virtual image.
d. Concave lenses produce only a real image.
____ 14. Which structure first refracts light rays entering the eye?
a. the pupil
c. the iris
b. the cornea
d. the lens
____ 15. What vision problem is experienced when light rays entering the eye from nearby objects cannot be refracted
enough, causing the image to fall into focus behind the retina?
a. astigmatism
c. near-sightedness
b. colour blindness
d. far-sightedness
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____ 16. What corrective measure works to correct far-sightedness?
a. A converging lens in front of the eye helps to prevent the cornea and lens from refracting
light too much, allowing an image to form on the retina.
b. A convex lens in front of the eye helps the cornea and lens to refract light enough to form
an image on the retina.
c. A diverging lens in front of the eye helps the cornea and lens to refract light enough to
form an image on the retina.
d. A concave lens in front of the eye helps to prevent the cornea and lens from refracting
light too much, allowing an image to form on the retina.
____ 17. If your eyeglasses have this shape, what vision problem do you likely have, and what is the name of the lens you
are using?
a.
b.
c.
d.
far -sightedness, being corrected with a converging lens
near-sightedness, being corrected with a converging lens
far-sightedness, being corrected with a diverging lens
near-sightedness, being corrected with a diverging lens
Completion
Complete each statement.
18. The part of the electromagnetic spectrum that we feel as heat is/are _________________________.
19. That colour of visible light with the shortest wavelength and highest frequency is ____________________.
20. The thin piece of wire electricity flows through in an incandescent bulb to generate light is the
____________________.
21. In a fluorescent light, electricity passes through a small amount of ____________________ such as mercury
vapour in the tube or bulb, producing UV radiation.
22. ____________________ materials allow some light rays through, but also absorb some rays, and may cause some
rays to reflect at various angles off their surfaces.
23. An object casts a(n) ____________________ shadow when it gets closer to the light source.
24. An area of partial shadow from a non-point source of light is called a(n) ____________________.
25. A concave mirror that produces an image 2 m tall from an original object that is 40 cm tall has a magnification of
____________________.
26. A spoon standing in a clear glass of water appears to be broken because water has a different
_________________________ than air.
27. ____________________ occurs when white light is refracted into the different wavelengths of colour it contains.
28. A(n) ____________________ occurs if light waves become refracted along boundaries between warm and cold air
of different densities.
29. Convex lenses are also known as ____________________ lenses because they refract light rays to a single point.
30. The vision problem shown below could be corrected using a(n) ____________________ lens.
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Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the
statement true.
____ 31. The top of a wave is known as the trough. ____________________
____ 32. Ultraviolet rays have more energy, a shorter wavelength, and higher frequency than visible light.
____________________
____ 33. The speed of light becomes slower when it enters a medium with a higher refractive index.
____________________
Short Answer
34. Describe the steps that occur when you flip a switch and allow electricity to flow to a fluorescent light.
35. What does LED stand for? How are LEDs different from other common sources of artificial light such as
incandescent and fluorescent lights?
36. How do light rays reflecting from a log in the water behave as they leave the water’s surface and enter the air
before reaching your eyes?
37. What type of lens is shown?
38. What effect does the lens have on parallel light rays passing through it?
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39. On which side of the lens — left or right — would the focal point appear to be?
40. What type of image does this lens form?
41. How would the image of an object appear if the object was placed at a distance 3 f from the focal point of a
convex lens?
Problem
42.
Where has the object been placed if a convex lens with a focal length of 23 mm produces a virtual image 16 mm
from the lens?