Light Activity Homework4/22 Thursday(Late Arrival)

Go over testIntro light / EM waves

Light Notes 20.4Get a protractor!

4/23 Friday HW quiz?Shades labDiscuss polarization / sunglasses

Read and take notes over Microwave & Greenhouse info EM Phet: Microwaves / Greenhouse Effect (due Tues)

4/26 Monda To discuss microwaves and greenhouse effectStart EM PHet

EM Phet: Microwaves / Greenhouse Effect Color Addition Internet Activity

4/27 TuesdayGo over HomeworkColor additionWhy sky blue / sunsets

Color Subtraction Internet Activity

4/28-4/29 PSAE

4/30 FridayGo over homeworkDiscuss color applications

Color WS & Color Phun

5/3 Monday Finish color applicationsTo discuss reflectionTo do Mirror Activity

Read and take notes over Ch 22-22.2 : Bring a protractor!

5/4 Tuesday Finish reflectionTo begin refraction / index of refraction

Reflection Practice (use a protractor and label everything)

5/5 Wednesday To discuss Snell’s LawBending Normally Lab

Read and take notes over Ch 22.3Finish Lab

5/6 Thursday To practice Snell’s LawTo discuss critical angle and total internal reflection

Snell’s Law ProblemsRefraction Problems

5/7 Friday Critical angle Lab Finish total internal reflection To start refraction applications

Diiamonds are Sparkly WSRefraction of Light/Atmospheric Refraction (use book)

5/10 Monday Finish refraction apps.Discuss rainbowsTo review for test

Work on review sheet

5/11 Tuesday Review for test Study for test!

5/12 Wednesday Test!! Newsletter Q’sLens Intro

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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.cfmhttp://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.

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Period ________ Name __________________________________________

Purpose To investigate the effects of polarized light.

Required Equipment/Supplies

2 small polarizing filtersLight source Small plane mirror

Discussion The vibrations of light waves reaching your eyes are mostly randomly oriented they vibrate in many planes at once. In polarized light, the light waves vibrate in one plane only. Polarized light can be made by blocking all the waves except those in one plane with polarizing filters. The filters can also be used to detect polarized light.

Procedure

Step 1: Position one polarizing filter between your eyes and a light source and slowly rotate the filter 360°. Observe the intensity of the light as seen through the filter. Note any intensity changes as you rotate the filter.

1. What happens to the intensity of the light as you rotate the filter?

___________________________________________________________________________

Rotate second filter Step 2: Arrange one filter in a fixed position in front of the light source Slowly rotate a second filter held between your eyes and the fixed filter. Note any intensity changes of the light as you rotate the filter 360°.

2. What happens to the intensity of the light as you rotate the filter?

___________________________________________________________________________

Rotate other filter Step 3: Hold the filter at your eye in a fixed position while your partner slowly rotates the other filter next to the light source 360°. Note any intensity changes of the light as the filter is rotated.

3. What happens to the intensity of the light as the filter is rotated.

___________________________________________________________________________

4. Note any relationship between any observed changes in the intensity of the light and the position (angle rotated 0-360 degrees) of the filter.

___________________________________________________________________________

___________________________________________________________________________

Physics Laboratory Manual © Addison-Wesley Publishing Company Inc. modifiede All rights reserved.Rotate both filters

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Step 4: Rotate both of the filters through one complete rotation in the same 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 anboard 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 thisviewing the desk to orientation and view the white board. While viewing the white boardthe 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?

___________________________________________________________________________

___________________________________________________________________________

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View sky through filter Step 10: On a sunny day, view the region of the sky close to and away from the sun. Rotate the filter 360° while viewing each region.CAUTION: Do not look at the sun!

12. What happens to the intensity of the light as you rotate the filter?

___________________________________________________________________________

___________________________________________________________________________

13. Is the light of the sky polarized? If so, where is the region of maximum polarization in relation to the position of the sun?___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________View LCD with filter Step 8: View a liquid crystal display (LCD) on a wristwatch or calculator using a filter. Rotate the filter 360° and note any intensity changes.

14. What happens to the intensity of the light as you rotate the filter?

___________________________________________________________________________

___________________________________________________________________________

15. Is the light coming from a liquid crystal display polarized?

___________________________________________________________________________Analysis (You will need to use your book, refer to steps 7and 8)16. Why do polarized lenses make good sunglasses?

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________17. Explain why the effects seen in Steps 1 to 3 occur.

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________Physics Laboratory Manual © Addison-Wesley Publishing Company Inc. All rights reserved.

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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”.

MicrowavesUse 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 EffectUse 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?)

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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?

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MicrowavesSome 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.

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Greenhouse EffectHere 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

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through the cloud (which is mainly water vapor).

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_VisionClick 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:

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8. In order for you to see anything, where does light have to go?

Why is the sky blue?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.

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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.)

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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: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 _______________.

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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.

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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__________________.

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Color PHUN

The following symbols indicate the color of an object in white light.

® ß Ω ¥ † © ∑ ≈≈RED BLUE GREEN YELLOW MAGENTA CYAN WHITE BLACK

1. If you shine green light on the different objects what color would they appear?® Ω ¥ © ∑

_______ _______ _______ _______ _______

2. If you shine magenta light on the different objects what color would they appear?¥ † ≈≈ © Ω

_______ _______ _______ _______ _______

3. If you shine yellow light on the different objects what color would they appear?∑ ß ® † ©

_______ _______ _______ _______ _______

4. If you shine blue light on the different objects what color would they appear?Ω ß ® † ©

_______ _______ _______ _______ _______

5. If you were jealous of your friend’s dazzling new red sweater, how could you make it turn black at the dinner table by changing the light bulb? In other words, what color would the light bulb need to be? Explain your answer.

6. Is it possible to make a green apple appear red by shining a certain color of light on it? Why or why not?

7. What color light should you shine on a yellow banana to make it appear green? There are two answers.

8. Define and give an example of complimentary colors or light.

9. Why are newer fire engines a yellow-green color? (Why are some street signs being painted this same yellow-green color?)

10. What is the result when red, green, and blue light combine together?

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Radiation Curvesa. 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

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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.

HUMANEYES

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?

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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.

EmergencyLook at the image below in a plane mirror. Describe what you see. Why is this on the front of an ambulance?

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Diamonds are SparklyRound 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.

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?

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table

ndiamond = 2.42

nair = 1

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.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 the chart below.

BE SURE THE LIGHT IS GOING FROM AIR TO WATER!

Analysis:1. What is the index of refraction (in words)? What is the equation for index of refraction?

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.

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Øi

ØR

0°

10°

20°

30°

40°

50°

60°

70°

80°

Angle of Incidence Øi

Measured Angle of Refraction ØR

calculate sinØi

calculate sinØR

6. Draw a best fit line for your graph and find the 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.

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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:1.

2.

3.

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Find the angle of refraction and draw it.

Find the angle of refraction and draw it.

Find the angle of refraction and draw it.

n1 = 1 (air)

n2 = 1.52 (glass)

n1 = 1.33 (water)

n2 = 1 (air)

n2 = 1 (air)

n1 = 1.52 (glass)

25o

40o

30o

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?

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Refraction Problems

Indices of RefractionMedium n Medium n

Vacuum 1.00 Crown Glass 1.52Air 1.00 Quartz 1.54Water 1.33 Flint Glass 1.61Ethanol 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.

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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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Name________________________

Things Are Getting CriticalObjective: 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

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occur in the Snell’s Law lab?

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Refraction ApplicationsTotal Internal ReflectionTotal 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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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. 716http://www.edumedia-sciences.com/en/a312-snell-s-lawhttp://dev.physicslab.org/Document.aspx?doctype=3&filename=GeometricOptics_RefractionPhenomena.xmlhttp://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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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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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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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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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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