1. Light Activity Homework
4/22 Thursday Go over test Light Notes 20.4
(Late Arrival) Intro light / EM waves Get a protractor!
4/23 Friday HW quiz? Read and take notes over
Shades lab Microwave & Greenhouse info
Discuss polarization / sunglasses EM Phet: Microwaves /
Greenhouse Effect (due Tues)
4/26 Monda To discuss microwaves and greenhouse effect EM Phet: Microwaves /
Start EM PHet Greenhouse Effect
Color Addition Internet Activity
Go over Homework Color Subtraction Internet Activity
4/27 Tuesday Color addition
Why sky blue / sunsets
4/28-4/29 PSAE
Go over homework Color WS & Color Phun
4/30 Friday Discuss color applications
5/3 Monday Finish color applications Read and take notes over Ch
To discuss reflection 22-22.2 : Bring a protractor!
To do Mirror Activity
5/4 Tuesday Finish reflection Reflection Practice (use a
To begin refraction / index of refraction protractor and label everything)
5/5 Wednesday To discuss Snell’s Law Read and take notes over Ch
Bending Normally Lab 22.3
Finish Lab
5/6 Thursday To practice Snell’s Law Snell’s Law Problems
To discuss critical angle and total internal Refraction Problems
reflection
5/7 Friday Critical angle Lab Diiamonds are Sparkly WS
Finish total internal reflection Refraction of Light/Atmospheric
To start refraction applications Refraction (use book)
5/10 Monday Finish refraction apps. Work on review sheet
Discuss rainbows
To review for test
5/11 Tuesday Review for test Study for test!
5/12 Wednesday Test!! Newsletter Q’s
Lens Intro
1
3. Light Notes:
20.4 Notes: Read section 20.4 or go to the following website and answer the
following questions:
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/electromagnetic/
1. Any charge moving or not will have what type of field around it?
2. A moving charge, in addition to #1, will also have what type of field around it?
3. A ___________ magnetic field produces a ____________ electric field.
4. A ___________ electric field produces a ____________ magnetic field.
5. Electromagnetic waves are transverse or longitudinal?
6. Label the different electromagnetic waves on the spectrum on the back of this page.
7. Which electromagnetic wave travels the fastest?
8. Which electromagnetic waves are most dangerous? Why?
22-22.2 Notes: Read 22-22.2 (including 22.1 insight) in your book or go to
the following websites to answer the following questions:
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/reflection/specular/
http://www.physicsclassroom.com/mmedia/optics/ifpm.cfm
http://dev.physicslab.org/Document.aspx?doctype=3&filename=GeometricOptics_PlaneMirrors.xml
1. Why is light reflection important?
2. In order for us to see anything what must happen?
3. Define the law of reflection with a diagram and equation.
4. Define angle of incidence, angle of reflection, and normal line.
5. What is the difference between diffuse (irregular) reflection and regular reflection?
6. Which light rays follow the law of reflection? Diffuse or regular reflection?
7. Why do you see such a bigger glare at night from a wet road than from a dry road?
8. Explain how images are formed by a plane mirror
22.3 Notes: Read 22.3 in your book or go to the following website to answer
the following questions:
http://micro.magnet.fsu.edu/primer/java/refraction/refractionmono/
1. Define refraction.
2. What causes refraction?
3. Define index of refraction. Include an equation.
4. What are the units for index of refraction?
5. If diamond has an index of refraction of 2.42 and water has an index of refraction of 1.33, does light
travel slower in diamond or water?
6. The larger the index of refraction the ____________ the light travels.
7. What is Snell’s Law?
8. If light travels from glass to air describe what will happen. Use words and a diagram.
3
6. direction
at the same time. Note any intensity changes.
5. What happens to the intensity of the light as you rotate both filters together?
_____________________________________________________________________________
Rotate both filters in Step 5: Rotate both of the filters through one complete rotation at the
opposite directions same time, but in opposite directions. Note any intensity changes.
6. What happens to the intensity of the light as you rotate both filters in opposite
directions?
_____________________________________________________________________________
Rotate single filter for Step 6: Repeat Step 1, except arrange the light source and a mirror so
light reflected off a that you observe only the light coming from the mirror surface. Note any
mirror intensity changes of the light as you rotate the filter.
7. What happens to the intensity of the light as you rotate the filter?
_____________________________________________________________________________
8. Is the light reflected off a mirror polarized?
_____________________________________________________________________________
Rotate single filter for Step 7: Repeat Step 1, view a light source so that you observe only the
light reflected off your light coming from the desk surface. Note any intensity changes of the
desk light as you rotate the filter. (This works best if viewed from at
least three meters from your desk)
9. Is the light reflected off a desk polarized?
_____________________________________________________________________________
Rotate single filter for Step 8: Repeat Step 1, view a light source so that you observe only the
light reflected off the light coming from the white board surface. Note any intensity changes
class room white of the light as you rotate the filter. (This works best if viewed from an
board angle, not straight on)
10. Is the light reflected off a white board polarized?
_____________________________________________________________________________
Compare the filter Step 9: View a light source reflected off a desk through a filter. Rotate
orientation when the filter to a position of minimum light intensity. Keep the filter in this
viewing the desk to orientation and view the white board. While viewing the white board
the white board rotate the filter 90 degrees. Note any differences observed.
11. Is there a difference in the light reflected off the desk and the white board?
_____________________________________________________________________________
_____________________________________________________________________________
6
8. EM Wave Phet Physics Simulations
For all of these demos go to the following website http://phet.colorado.edu, click on go to the simulations
and click on “Light and Radiation”.
Microwaves
Use the simulation and the note page about microwaves in this packet to answer the following
questions.
1. For a microwave oven to heat food the food must contain what?
2. The blue part of the molecule represents which atom? red parts?
3. You can adjust the frequency and amplitude using the sliders or click on the box and type it in. Select
“one molecule” from the menu up top. Turn the microwave on and describe what the molecule does and
why. (Be sure the field view is NOT on “none”)
4. Most food that you heat up is going to contain many water molecules so select “many molecules” from
the menu up top. Slide the amplitude down to 0.20. We are doing this because it will be easier to see
resonance if the amplitude is lower. Try the following frequencies (a) 0.00099 (b) 0.0015 (c) 0.00246 (d)
0.00300. Be sure you reset before trying a new frequency and allow the simulation to run about a minute.
Observe the temperature gauge for each frequency. Which frequency causes the temperature to
increase the most?
5. Relate your answer to #4 to resonance and natural frequency.
Greenhouse Effect
Use the simulation and the greenhouse effect note page in this packet to answer the following
questions. You will need to click on “Heat and Thermo” in the left column and then select “Greenhouse
Effect”.
1. Select “Glass Layers” from the top menu. Add one pane of glass and be sure “thermometer” and
“view all photon” is selected. What happens to the sunlight photons when they hit the glass? Why?
2. What happens to the sunlight photons when they hit the ground? Why?
3. If infrared waves cannot pass through glass explain how you think the infrared photons leave the
glass? (Hint: What happens to glass if it sits in the sun?)
8
9. 4. Explain why so many infrared photons get trapped inside the glass.
5. Explain why you car gets so hot if left in the sun with the windows rolled up.
6. Select “Greenhouse effect” from the top menu. Select “no greenhouse gases” and describe what
happens to the sunlight photons and the infrared photons.
7. Select “today” and describe what the little flashes represents. After you let the simulation run for a
minute or two describe where most of the infrared photons get trapped and why.
8. Select “no greenhouse gases” and add some clouds. If there are too many photons, unclick “view all
photons”. Most of the time what do the clouds do to the infrared photons?
9. Why are cloudy nights typically warmer than clear nights?
10. If you are sunbathing and a cloud comes between you and the sun, why do you feel so much cooler?
9
10. Microwaves
Some basic information:
1. The source of microwaves (like all electromagnetic
waves) are accelerated charges.
2. The higher the frequency the more energy carried in
each wave. (Photons carry this energy.) This is why
gamma rays and X-rays are so dangerous to human cells.
(Gamma ray photons carry more energy than microwave
photons). These high frequency EM waves are more
likely to cause your cells to mutate and cause cancer.
3. Microwaves are low frequency EM waves and are less
likely to cause your cells to mutate than visible light.
Observe where microwaves are on the EM spectrum. A
light bulb is more likely to give you cancer than a
microwave.
4. Microwaves have relatively long wavelengths (from
about 1 cm to 1 meter).
How a microwave oven heats your food:
1. The food must have water in it. If there is no water the
object will not heat up.
2. Water is a polar molecule, meaning one side has a
positive charge (the hydrogen atoms) and the other side
has a negative charge (the oxygen atom).
3. Normally these water molecules (in the food) are randomly orientated. (Top right diagram) When
exposed to an electric field these molecules tend to line
up. (middle right diagram)
4. If these molecules are exposed to an electric field that
moves back and forth (as from an EM wave) the molecules
will rotate back and forth. (bottom right diagram) When
these water molecules rotate back and forth, they rub past
each other and heat up due to friction.
5. Microwaves used in a microwave oven have the perfect
frequency to allow the water molecules to rotate the most. In
other words, microwaves match the rotational frequency of
water molecules or the microwaves will cause the water
molecules to resonate.
Common Questions:
1. What happens if you put metal in a microwave? The microwaves will cause charge to move back and
forth in the metal (because of the electric field). If the metal is thin, it will heat up. If the metal is pointy,
the charge will leak off (similar to a lightning rod) this could cause sparks in the microwave.
2. Are microwaves likely to cause cancer? No, in fact visible light carries more energy than
microwaves.
3. Why can you see in a microwave, but the microwaves cannot exit? The door is covered with
small holes. These holes are large enough for visible light to exit but too small for microwaves to
exit. Refer to the wavelengths of each wave.
10
11. Greenhouse Effect
Here is the situation: Your car is sitting outside on a nice 60° sunny day. After sitting in the sun for a few
hours you get in your car and only to discover is really HOT inside. WHY?
Some basic information:
1. Three main types of electromagnetic waves come from the sun. These waves are ultraviolet (gives
you a suntan or sunburn), visible (you can see in sunlight), and infrared (you feel warmth in sunlight).
2. Of these three EM, visible light is the only one that can go through glass. You can see through glass
but cannot get a suntan through glass.
3. White visible light (like from the sun) is really a combination of all colors of light.
4. An object’s color is determined by the color it reflects. All the other colors get absorbed. (i.e. a red
object will reflect red light and absorb all the other colors)
5. When these other colors get absorbed, they change into infrared light (infrared light has less energy
than visible light).
6. Black absorbs all the colors and white reflects all the colors. In the summer if you go outside in a black
shirt you feel much warmer than if you go outside with a white shirt.
Why your cars gets hot sitting in the sun:
1. So your car sitting in the sun with the windows rolled up will have UV, visible, and IR waves hitting it.
2. Of these waves only visible can go into the car, see diagram below.
3. The visible light enters and hits the car’s interior. (If the interior is blue then blue gets reflected and the
other colors get absorbed.)
4. The absorbed light changes to infrared.
5. This infrared light cannot exit the glass so it gets trapped inside. This trapped IR causes your car to
get hot.
6. If you put a sunshade in the windshield this will prevent most of the visible light from entering the car
so less light turns into infrared and hence less heat.
7. If you crack your windows, this will allow some of the IR waves to escape.
How does this relate to the greenhouse effect with the Earth?
1. Greenhouse gases (carbon dioxide and water vapor, which you get from burning fossil fuels) act
similar to glass in sense that they do not allow IR to pass through. If there is too much greenhouse gases
in the atmosphere the IR waves (created after visible light was absorbed) cannot escape into space and
the planet heats up. Greenhouse gases do however transmit UV (you can get a sunburn on a cloudy
day).
2. Recall a time when you were laying in the sun and then a cloud come between you and the sun. It
feels cold but not because the temperature dropped. You feel cold because the IR waves are not getting
through the cloud (which is mainly water vapor).
11
12. Color Addition (all about lights)
Basics:
Use the following website to answer the following questions:
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/additiveprimaries/index.html
1. What are the primary colors for color addition (light)? Label
the colors on the diagram and then use the appropriate colors and
actually color them in.
2. Why are these called primary colors?
3. Write what color you get when you mix the following colors of
light together.
Red light + blue light = __________________
Red light + green light = _________________
Blue light + green light = _________________
Red + Blue + green light = ________________
Cyan light + red light = ___________________
Yellow light + Blue light = ________________
Magenta light + green light = ______________
4. What are complementary colors? Give an example of 2 colors that are complementary.
Color and Your Eyes:
5. Describe how human eyes perceive a color like yellow.
6. Describe why you think a TV would use red, green, and blue to produce pictures.
Use the following website: http://phet.colorado.edu/simulations/sims.php?sim=Color_Vision
Click on “run now!” wait for the simulation to start and then select “RGB bulbs” from the top menu.
7. Play with the sliders and describe how you make orange, violet, and brown.
Orange: Violet: Brown:
8. In order for you to see anything, where does light have to go?
Why is the sky blue?
12
13. Use the following website: http://optics.kulgun.net/Blue-Sky/
9. If there was no atmosphere what color would the sky look?
10. What color is sunlight? What three colors can you use to make white?
11. What is the one key word to explain why the sky looks blue?
12. Which color has the shortest wavelength? Longest wavelength? Why does our atmosphere scatter blue
light the best?
13. Why does the sky look bluer directly overhead and more whitish near the horizon?
14. This part is not on the webpage so you will need to use your brain.
a. What color is the sun during the day?
b. What 3 colors make up sunlight?
c. If blue gets scattered away what 2 colors are left?
d. When you add the 2 colors from part c, you get….
e. Write a sentence that explains why the sun looks yellow during the daytime.
15. At sunrise or sunset, the sunlight must travel through _________ atmosphere. All the colors except
red get ___________ away leaving only red light to get to you.
16. Use this website: http://optics.kulgun.net/Blue-Mountains/ and describe why mountains or object far in
the distance tend to look bluish.
13
14. Color Subtraction (taking light away)
Basics:
Use the following website (and your brain) to answer the following questions:
http://micro.magnet.fsu.edu/optics/lightandcolor/primary.html
Scroll down until you see this sentence “Thus far this discussion has centered on the properties of visible
light with respect to the addition and subtraction of transmitted visible light, which is often visualized on
the screen of a computer or television.” Answer the following questions.
1. What is the difference between color addition and color subtraction?
2. A red apple reflects what color? A red apple absorbs (subtracts) what colors?
3. a. A cyan object reflects what colors? A cyan object absorbs (subtracts) what color?
3. b. If a cyan object were placed in yellow light what color would it appear? (What colors make up
yellow? What happens when these colors strike a cyan object?)
Color Filters:
Click on color filters to take you to this page:
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/colorfilters/index.html
4. A red object __________ red light and absorbs __________ and __________ light.
5. A red filter allows _______ light to pass through and absorbs _________ and __________ light.
6. If a green filter is placed over a blue object the object will appear ___________ because no light makes
it through.
Color Printing:
Click back and then scroll down to color separation to take you to this page:
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/colorseparation/index.html
7. What are the subtractive primary colors? Explain why these colors are used for printing.
8. Drag the yellow on top of the cyan. What color shows up more (i.e. what color does yellow and cyan
have in common)? (Observe the apple on the left and the kiwi.)
9. Drag the cyan on top of the magenta. What color shows up more (i.e. what color does cyan and magenta
have in common)? (Observe the apple on the left and the kiwi.)
10. Drag magenta on top of yellow. What color shows up more (i.e. what color does magenta and yellow
have in common)? (Observe the apples on the rights.)
Color Shadows:
14
15. Go to the following website: http://www.learner.org/teacherslab/science/light/color/shadows/index.html
11. Explain using color addition why the background is yellow.
12. a. Explain how you get a red shadow. (What color do you start with and what color is being
subtracted?)
12. b. Explain how you get a green shadow.
13. Move the lights back and forth and describe how you get a black shadow.
Ocean Cyan:
You will need to use what you have learned so far and your brain to answer the following questions.
14. Which electromagnetic wave interacts best with water? (Hint: Look back at previous concepts and the
electromagnetic spectrum.)
15. Of the visible spectrum, which color is closest to #14?
16. Because __________________ (#14) cause water to essentially resonate, they get absorbed quickly
by water. Because __________________ (#15) is the color closest to __________________ (#14),
________________ (#15) slowly gets absorbed by water. If you started with white light and remove
________________ (#14) you are left with _____________ and ________________ which added
together give you __________________.
17. If a red lobster was at the bottom of the ocean and had only cyan light shining on it, this blue and
green light would be _______________, making the lobster appear _______________.
15
16. Some answers will be more than one color!
1. Red light + Blue light __________________
2. Green light + Blue light __________________
3. Green light + Blue light + Red light _____________
4. Magenta light + Cyan light ________________________
5. Magenta light + Green light ________________________
6. Green light + Red light ________________________
7. Yellow light + Cyan light ________________________
8. White light – Yellow light ________________________
9. White light – Red light ________________________
10. Magenta light – Blue light ________________________
11. A cyan filter allows _______________________light to pass through it.
12. A red filter allows _______________________light to pass through it.
13. A green filter allows _______________________ light to pass through it.
14. A yellow filter allows _________________________ light to pass through it.
15. A blue filter allows _______________________light to pass through it.
16. A blue filter absorbs ________________________ light.
17. A yellow filter absorbs ________________________ light.
18. A green filter absorbs ________________________ light.
19. A magenta filter absorbs ________________________ light.
20. A cyan filter absorbs ______________________________ light.
21. A blue filter placed over a cyan filter will allow _________________________ light through.
22. A red filter placed over a green filter will allow __________________________ light through.
23. A magenta filter placed over a clear filter will allow ________________________ light
through.
24. A yellow filter placed over a green filter will allow ________________________ light through.
25. A cyan filter placed over a yellow filter will allow__________________________ light through.
16
17. 1. Yellow paint absorbs ___________________________ light.
2. Green paint absorbs ___________________________ light.
3. Cyan paint absorbs ___________________________ light.
4. Blue paint absorbs ___________________________ light.
5. Black paint absorbs ___________________________ light.
6. Blue paint reflects ___________________________ light.
7. Magenta paint reflects ___________________________ light.
8. Red paint reflects ___________________________ light.
9. White paint reflects ___________________________ light.
10. Yellow paint reflects _________________________ light.
11. In order to get a true green color, an artist would mix ____________________ paints.
12. In order to get a true red color, an artist would mix _______________________paints.
13. In order to get a true blue color, an artist would mix _______________________paints.
14. Magenta paint mixed with yellow and cyan paints produce ___________________________
A color must be in the light in order to be reflected!
15. A piece of cyan paper illuminated with red light will look __________________.
16. A piece of magenta paper illuminated with red light will look __________________.
17. A piece of blue paper illuminated with red light will look __________________.
18. A piece of blue paper illuminated with yellow light will look__________________.
19. A piece of red paper illuminated with green light will look__________________.
20. A piece of yellow paper illuminated with red light will look__________________.
21. A piece of black paper illuminated with red light will look __________________.
22. A piece of white paper illuminated with red light will look __________________.
23. A piece of yellow paper illuminated with yellow light will look__________________.
24. A piece of white paper illuminated with green light will look__________________.
25. A piece of green paper illuminated with red light will look__________________.
17
19. Radiation Curves
a. 28.4 – Sunlight
i. Why do objects appear different colors in different types of lighting
(e.g. candle flame, incandescent lamp, fluorescent lighting,
daylight)?
ii. Sunlight emits all frequencies but is strongest in the yellow-green
region.
SUNLIGHT INCANDESCENT LIGHTS
FLUORESCENT LIGHTS BLACK LIGHTS
19
20. 2. Why do clothes sometimes seem like they match in a department store but not when you go
outside?
3. Draw the cone sensitivity for human eyes on the diagram.
HUMAN
EYES
4. How does the sensitivity of the different cones
compare to the brightness of sunlight? Why?
Why are modern fire trucks painted yellow-green?
1. Why are fire trucks painted their yellow-green?
2. Tennis balls used to be white. What advantage is there to making tennis balls yellow-green?
3. Many road signs are being repainted. What advantage is there to having yellow-green road
signs?
4. What color(s) are our eyes most sensitive to? Why?
20
22. Where’s that image?
Use a plane mirror (with the wood on the back) and 2 pencils with rubber stopper stands. Place the
pencil in front of the mirror and look in the mirror at the image. Now take the second pencil and stand it
so it appears to be directly on top of the image. If you move your head back and forth the pencil should
stay lined up with the image.
Measure how far the object is from the front of the mirror. do = __________
Measure how far the image is from the front of the mirror. di = __________
Draw it on the diagram.
How much mirror do you need?
From doing the previous activity, how does the object distance compare to the image distance?
How does the object size compare to the image size?
Using a ruler, draw Bob’s image. Be sure and get the size and distance away from the mirror accurate.
If Bob is going to see his image light must go to his eyes. Draw a line from the image’s feet to Bob’s
eyes. We know that light doesn’t actually come from behind the mirror to Bob’s eyes but instead goes
from his actual body and reflects. Draw a light ray from Bob’s feet to where the image’s line crosses the
mirror. Use a protractor to verify that this light ray will follow the law of reflection. Label the normal line
and the angle of incidence and angle of reflection on the diagram above. Repeat for the top of Bob’s
head. Compare the mirror height used to Bob’s height.
Emergency
Look at the image below in a plane mirror. Describe what you see. Why is this on the front of an
ambulance?
22
23. Diamonds are Sparkly table
Round brillant diamonds are cut to sparkle the most. The reason that a diamond
sparkles is because any light that enters the top (the table) can only exit the top (table).
1. Draw and then calculate the critical angle for diamond in air.
2. Draw a light ray so that it hits the surface of the diamond any place on the table. Use a protractor and
your knowledge of Snell’s Law and critical angle to determine where the light ray will exit the diamond.
Draw everything out on the diagram below.
3. Repeat #2 for a different light ray.
nair = 1
ndiamond = 2.42
4. What happens to the light rays when they hit the bottom of the diamond? Why?
5. Compare your diagram to a classmates. Did they get the same results?
23
24. Name _____________________
Bending Normally (Snell’s Law Explored)
Objective: To determine the relationship between the angle of incidence and the angle of refraction for
light changing mediums.
Procedure:
1. Fill the plastic semicircle with water.
¯ i 2. Use the laminated paper (be sure the side that says REFRACTION in
the corner is up).
3. Shine the light along the incident angles and then observe the refracted
angles on the other side. Record these refracted angles in the chart
below.
4. Use your calculator and calculate sinØi and sinØR and record these in
¯ R
the chart below.
BE SURE THE LIGHT IS GOING FROM AIR TO WATER!
Angle of Measured Angle
calculate calculate
Incidence of Refraction
¯ i ¯ R
sin¯ i sin¯ R
0¡
10¡
20¡
30¡
40¡
50¡
60¡
Analysis: 70¡
1. What is the index of refraction (in words)? What is the equation for index of refraction?
80¡
2. If the light slows down more will the index of refraction be higher or lower?
3. Why doesn’t the index of refraction have units?
4. Are light rays reversible? Why or why not? (If you are not sure, try it. Pick an angle and turn the ray
around and see if it travels where you predicted)
5. Graph sinØi (Y axis) vs sinØR (X axis) on the back of this page. Be sure and follow good graphing
techniques.
24
25. 1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
6. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Draw a best fit
line for your graph and
find the sin¯ R slope. slope =
________________
7. Write an equation for the slope with variables only?
8. If the relationship between Øi and ØR is defined by Snell’s Law (n1sinØ1=n2sinØ2) then write an equation
for the slope of your line in terms of the indexes of refraction only.
9. If you used a semicircular piece of glass instead of water, how would the graph change? Explain your
reasoning. (For extra credit: collect data and graph the data for a semicircular piece of glass)
10. If you had a semicircular piece of glass resting in water (the light is going from water to glass instead
of going from air to water), how would the graph change. Explain your reasoning.
11. Light travels from flint glass (n=1.66) to diamond (n=2.42). If you were to make a graph of sinØi vs
sinØR, determine what the slope of the line would be.
25
26. Snell’s Law Problems
Givens:
Anytime the problem does not state the medium, assume it is air (n=1).
c= 3 x 108 m/s
Problems: Find the angle of refraction and draw it.
1.
n1 = 1 (air)
25o
n2 = 1.52 (glass)
2.
Find the angle of refraction and draw it.
40o
n1 = 1.33 (water)
n2 = 1 (air)
3.
Find the angle of refraction and draw it.
n2 = 1 (air)
n1 = 1.52 (glass)
30o
26
27. 4. A flashlight beam strikes the surface of a pane of glass (n=1.52) at a 45o angle. What is the angle of
refraction?
5. A diver shines a flashlight upward from beneath the water (n=1.33) at a 30o angle to the normal. At
what angle does the light leave the water?
6. The angle of refraction of sunrays after they enter water is 20o. Find the angle of incidence.
7. The speed of light in ice is 2.29 x 108 m/s. What is the index of refraction of ice?
8. If the index of refraction of glass is 1.52, what is the speed of light in glass?
27
28. Refraction Problems
Indices of Refraction
Medium n Medium n
Vacuum 1.00 Crown Glass 1.52
Air 1.00 Quartz 1.54
Water 1.33 Flint Glass 1.61
Ethanol 1.36 Diamond 2.42
1. Light travels 3.00 x 108 m/s through space. How far can light travel in one year? This is called
one light year.
2. The distance between our sun and the next nearest star is 4 light years. Change 4 light years into
meters.
3. Light is incident upon a piece of crown glass at an angle of 60.0o. What is the angle of refraction?
4. A ray of light passes from air into water at an angle of 30.0o. Find the angle of refraction.
28
29. 5. Light goes from flint glass into ethanol. The angle of refraction in ethanol is 25o. What is the angle
of incidence in the glass?
6. A ray of light travels from air into a liquid. The ray is incident upon the liquid at an angle of 30o.
The angle of refraction is 22.0o. What is the index of refraction?
7. What might the liquid in #6 be?
Extra Credit:
A ray of light is incident upon a 60-60-60 degree glass prism (n = 1.5) as shown in the figure
below. Using Snell’s Law, determine the angle r to the nearest degree. Using geometry, determine angle
A, B, C, and D.
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30. Name________________________
Things Are Getting Critical
Objective: To measure the critical angle for two substances and observe the phenomenon of total
internal reflection. To compare the observed critical angle with the calculated critical angle.
Procedure:
1. Fill the plastic semicircle with water.
2. Use the laminated paper (be sure the side that says CRITICAL ANGLE is facing up).
3. Shine the light along the incident angles and then observe the refracted angles on the other side.
Record these refracted angles in the chart below (for water in air).
4. At some angle, the light will no longer refract, but will reflect off the flat side of the block. You need to
try and find this angle as precisely as possible. This is the CRITICAL ANGLE. Record it below each
chart.
5. Repeat the above steps for the semicircle of glass.
WATER GLASS
Critical Angle for water in air = _____ Critical Angle for glass in air = _____
Analysis:
1. Draw a diagram for each substance showing what happens to the light at the critical angle. Use
Snell’s
Law to calculate the critical angle for each substance in air.
2. Why does total internal reflection take place when going from water/glass to air? Why did this event
not
occur in the Snell’s Law lab?
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32. Refraction Applications
Total Internal Reflection
Total internal reflection is a very
cool application of refraction and
Snell’s Law. This occurs when
light traveling inside a material is
reflected instead of refracted.
There is a certain angle called
the critical angle where the light
just grazes the surface of the
material (θair = 90o). See
diagram. At every angle greater
than the critical angle, the light is
totally reflected. The critical
angle for water is 48o so this
means when the incident angle is
greater than 48o you get total
internal reflection.
Diamonds work on this principle. All light that enters a diamond will
only exit through the top of the diamond – causing it to sparkle.
Fiber optics also work on this principle.
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33. Use the included websites and your book in order to best answer the following questions
Refraction of Sound
Visit: http://www.kettering.edu/~drussell/Demos/refract/refract.html
1. Does sound refract?
2. What causes sound to refract?
3. Why does sound travel farther on cold days? Explain and draw a diagram
Refraction of Light (22.3) p. 716
http://www.edumedia-sciences.com/en/a312-snell-s-law
http://dev.physicslab.org/Document.aspx?doctype=3&filename=GeometricOptics_RefractionPhenomena.xml
http://www.stmary.ws/highschool/physics/home/notes/waves/refraction/Refraction.htm
1. Will a full pool appear shallower, deeper, or the same depth as the same pool empty?
2. If you were spear fishing, would you have to aim higher or lower than where the fish appears to
be?
3. In the diagram, identify the real fish and the image of
the fish. Why do you see the fish at that point?
4.Watch this video (http://www.youtube.com/watch?gl=IE&hl=en-
GB&v=fhBZ40jIo4Q). Where would the archer fish need to aim in
order to hit the bug?
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34. Atmospheric Refraction (22.3) p. 714 – 717
Visit: http://www.physicsclassroom.com/Class/refrn/u14l4c.cfm
1. Explain how mirages occur. (Hint: compare to refraction of sound.) Draw a diagram to help.
2. How is it possible to see the sun after it is already below the horizon?
3. What causes the refraction in #2?
4. Why does the sun or moon appear to have a flat bottom near the horizon?
Rainbows & Dispersion (insight 22.4) p. 722
For this section you will need to watch the movie via a computer. As you are watching, you will need to
answer the questions below. Feel free to pause the movie at any time or re-watch any part.
1. What is dispersion? Why is dispersion important when describing rainbows?
2. What happens when white light enters a new medium?
3. Which color bends the most when going through a different medium? Why?
4. Which color bends the least when going through a different medium? Why?
5. Explain where the sun and raindrops need to be in order for you to see a rainbow.
6. What happens when light enters a raindrop? Describe the whole
process from when light enters the raindrop to when it exits.
Relate this to the picture to the right.
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35. 7. Label (or color) the colors (ROYGBV) in the rainbow
8. Why are the colors in a rainbow always in a
particular order? Relate you answer to the
picture.
9. Review the steps that must occur for you to see a rainbow. Use the following simulation to help:
http://www.edumedia-sciences.com/en/a60-rainbow
10. Why does each person have his or her own individual rainbow?
Be sure and watch the entire movie and read the last scene. After you are done, open some of the
other pictures on the CDrom and notice the order of the colors in the primary rainbow vs. the order of
the colors in the secondary window.
11. Why are the colors in a secondary rainbow reversed? Relate your answer to the picture.
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40. Light Review
EM Spectrum:
1) Which wave travels the fastest?
2) Which wave has the most energy?
3) Which wave has the smallest wavelength?
4) How big is the visible spectrum?
5) Describe how a microwave oven heats food.
6) Describe why your car gets hot with the windows rolled up and it sitting in the sun.
Polarization:
1) What is polarized light?
2) How would you determine if a light source is polarized?
3) Explain why 2 polarizing filters rotated opposite ways will go light to dark.
4) What is the advantage of polarized sunglasses? Describe the physics.
Color Addition / Color Subtraction:
1) How do you know you are doing color addition? Color subtraction?
2) Yellow object in cyan light =
3) Blue light + red light =
4) A magenta filter allows ____________ to pass through and absorbs ___________.
5) A cyan object looks cyan because it ___________ blue and green light and _________ red light.
Color Applications:
1) Why is the sky blue?
2) Why does the sun look yellow at noon and red at sunrise/sunset?
3) Why does ocean water look cyan?
4) Why are school crossing signs painted an annoying yellow-green color?
5) Explain how clothes can change color in a department store versus sunlight.
Law of Reflection:
1) What is the law of reflection? Draw a diagram.
2) When doesn’t the law of reflection hold true?
3) When measuring, you must always measure from what?
4) What is the difference between smooth and diffuse reflection?
Mirror Basics:
1) If you are standing 1.5 meters in front of a mirror, how far away from you is your image? Draw a
diagram.
2) What is written on the front of an ambulance? Why?
3) Describe the image seen in a plane mirror.
4) Draw a diagram showing how a person is able to see his feet in a mirror.
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41. Refraction / Index of Refraction:
1) What is refraction? What causes refraction?
2) Explain how using vegetable oil you can make a test tube disappear.
3) The index of refraction for plastic is 1.46. How fast does light travel in plastic?
4) If light goes from a high n to a low n, the light (speeds up/slows down) and bends (away/towards)
normal line.
Snell’s Law / Snell’s Lab:
1) A light ray traveling in water (n=1.33) hits the surface of a piece of glass (n=1.52) at an angle of
40°. Determine the angle of refraction.
2) You graph sinØi vs. sinØr. If the incident substance is water (n=1.33) and the slope is 1.82, what is
the other substance?
3) A light ray exits water into the air at an angle of 50°. What was the angle of incidence?
4) You graph sinØi vs. sinØr. You started with the light going from air to water. Then you make a
graph of light going from air to glass. Which graph is steeper and why?
Critical Angle / TIR:
1) When do you have to worry about the critical angle? Why?
2) Draw a diagram showing light going from glass (n=1.52) to air at the critical angle.
3) Describe the physics behind fiber optic cables work.
4) Describe the physics behind a diamond sparkling. Draw a diagram.
Refraction Applications:
1) How does a mirage occur?
2) How does a rainbow occur?
3) If you were spear fishing would you have to aim above or below where you see the fish? Draw a
diagram.
4) An empty pool will appear (shallower/deeper) than a full pool.
5) What causes sound to refract?
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