Unit 12: Behavior of Light: Reflection, Refraction, Diffraction, Interference

Unit MenuChapter 29Lessons 1 - Reflection and Refraction 1.1 Quick Lab – Images, Images and More Images! 1.2 Web Walk – Law of Reflection 1.3 Web Walk – Reflections and Curved Mirrors 1.4 Lab Simulation – Reflections in a Plane Mirror 1.5 Web Walk – Refraction, Snell's Law, and Internal Reflection 1.6 Lab Simulation – Snell's Law 1.7 Lesson Wrap Up – Quiz – Reflection and RefractionChapter 30Lesson 2 - Lenses - To Diverge or to Converge 2.1 Web Walk – Converging and Diverging Lenses 2.2 Quick Lab – A Lensless Lens!

2.3 Lab Activity – Images, Images and a Convex Lens!Knowledge Check

2.5 Lesson Wrap Up – Quiz - LensesChapter 31Lesson 3 - Diffraction and Interference 3.1 Web Walk – Interference and Wave Behavior 3.2 Quick Lab – Rainbows, Bubbles & More!Lesson 4 - Unit Wrap Up – Behavior of Light Exam

Learning GoalsBy the end of this unit, you will be able to:

* distinguish between regular and diffuse reflection of light * state the law of reflection (law of mirrors) * distinguish between real and virtual images * describe the characteristics of an image produced by a plane mirror * draw ray diagrams showing how an image is produced by a plane mirror * identify a curved mirror as converging (concave) or diverging (convex) * for plane and curved mirrors, identify any of the following on appropriate diagrams:

incident ray reflected ray angle of incidence angle of reflection normal principal axis center of curvature principal focus (focal point) focal length

* describe the characteristics of images produced by converging and diverging mirrors * conduct an experiment to determine the focal length of a concave mirror * draw accurate ray diagrams for both concave and convex mirrors to show how an image is produced * use the mirror formulas to locate and describe the image formed by convex and concave mirrors * describe some of the uses of plane and curved mirrors * define index of refraction * solve problems using Snell's law, involving:

index of refraction angle of incidence angle of refraction

* define critical angle and total internal reflection * describe total internal reflection, its effects, and its applications * solve problems involving total internal reflection * identify a lens as converging (convex) or diverging (concave) * for lenses, identify any of the following from an appropriate diagram:

incident ray normal refracted ray

angle of incidence angle of refraction principal axis principal focus (focal point) focal length

* conduct an experiment to determine the focal length of a convex lens * draw accurate ray diagrams for both convex and concave lenses to show how an image is produced * describe the characteristics of images produced by converging and diverging lenses * use the lens formulas to locate and describe the image formed by convex and concave lenses * describe the effects of aberration in lenses * give examples of common devices that refract light * describe and give examples of common applications of the following wave phenomena

reflection refraction diffraction interference (superposition principle) Doppler shift scattering (dispersion)

* explain the causes of bright and dark interference bands (fringes) of light * describe and compare single slit interference with double slit interference patterns * describe the causes of visible diffraction of waves * describe the properties of laser light

Check it out!

As members of The Students Alert for Physics Principles (SAPP) your mission is the help others understand the behavior of light – so they can have a reflective experience. Reflection, refraction, interference and diffraction are phenomena that are not always easily understood by the person wanting to connect to the world of the physics and the behavior of light. The SAPP is listed as the featured speaker/s at the Physics Wannabees Conference in Des Moines , Iowa . Your topic to discuss is “She comes in colors everywhere!” Remember - there is more to the behavior of light than meets to eye!

There is more to the behavior of light than meets the eye! Most people associate reflection with mirrors, rainbows with rain showers, mirages with roadways, refraction with lenses, glass, and water, and prisms with the separating the colors of light. A common misconception is that light only travels in a straight line. When

light encounters a different substance, its path will change. The behavior of light during reflection, refraction, diffraction, and interference will be studied during this unit. Questions to consider while studying this unit include: How do lenses and mirrors work? How do “light pipes” work? What is a mirage? As light and matter interact, light can be reflected, refracted, diffracted, transmitted, absorbed, dispersed, polarized and experience interference. Through the course of this unit, you will look at each of these interactions. The nature of light and its effects should become more meaningful to you once you understand their importance.

Lesson 1: Reflection and Refraction

“If you can't see my mirrors, I can't see you!” Where have you seen this statement? Right! – On the back of trucks ahead of you on the interstate. Reflections are interesting. Reflections of reflections are fascinating. Reflections of reflections of reflections … are kaleidoscopes! There are places in the world where, in late afternoon and early evening, mountains can be seen rising out of the horizon on the ocean. The mountains are real, but they are too distant to be seen normally. The question that probably comes to mind is – Why is this? How is this possible? Other questions to ponder are: What causes “ghosting” of distant objects in double-walled windows? Why is your image in a spoon upside down if you look into the bowl, but right side up if you look at the back? Why do you see better underwater when you wear goggles? After completing this lesson, you will be able to explain these phenomena!

12.1.1 Quick Lab – Images, Images and More Images!

Problem: How does reflected light travel to your eyes?

Procedure: A. Set a mirror in the middle of a sheet of paper and support it at the edges either by holding the mirror or using a small piece of clay. Place the pencils in the rubber stoppers and stand one of the pencils about 5 cm in front of the mirror. Looking at the image of the pencil in the mirror, place the second pencil behind the mirror where the image of the first pencil appears to be. If you have located the image correctly, the image of the first pencil and the second pencil itself will remain “together” as you move your head from side to side. Draw a line along the front edge of the mirror and mark the position of the pencils. Remove the pencils and the mirror from the paper. Measure the distance (d o ) from the object (the first pencil) to the mirror and the distance (d i ) of the image (second pencil) to the mirror. Draw the path you think the light takes from the first pencil to your eye as you observe the image.

B. Set two mirrors on edge on a protractor at a right angle to each other (Use clay to support them). Place a coin or a map pin between the two mirrors. Count the images produced. Keeping the map pin between the mirrors, reduce the angle to 72 o and count the images produced. Reduce the angle by 5 o at a time, and count the number of images that form at each angle. Prepare a table to record the data collected.

Analysis:

1. How did the distance (do) from the first pencil to the mirror compare with the distance (di) of the image to the mirror? 2. What happens to the number of images when you decrease the angle between the two mirrors? 3. Explain the reason for the multiple images you have observed. 4. Using the information that you have gained, explain the construction and the operation of a kaleidoscope.

Conclusion: What have you learned?

12.1.2 Web Walk – Law of Reflection aka: Law of Mirrors

Go to http://www.physicsclassroom.com/Class/refln/ (The Physics Classroom – High School Physics Tutorial) Lesson 1: Reflection and Its Importance “The Role of Light to Sight”. Complete the lesson noting the diagrams and the bold red terms. Click NEXT to go to “The Line of Sight”. Complete the lesson noting the diagrams, the bold terms and complete the Check Your Understanding. Click NEXT to go to “The Law of Reflection”. Complete the lesson noting the diagrams, the bold terms, view the animation, and complete the Check Your Understanding. What is the law of reflection? Click NEXT to go to “Specular and Diffuse Reflection”. Complete the lesson noting the diagrams, the bold terms and complete the Check Your Understanding. How are the types of reflections different? Click Go to Lesson 2 (Image Formation in Plane Mirrors). Complete “Why Is An Image Formed?” noting the diagrams, the bold terms, and the animations. Click NEXT to go to “Image Characteristics”. Complete the lesson noting the diagrams, the bold terms, and complete the Check Your Understanding. What is a virtual image? Click NEXT to go to “Ray Diagrams”. Complete the lesson noting the diagrams, the bold terms, and complete the Check Your Understanding. What is the fundamental rule is followed when constructing ray diagrams? Click NEXT to go to “What Portion of a Mirror is Required?”. Complete the lesson noting the diagrams and complete the Check Your Understanding.

Click NEXT to go to “Right Angle Mirrors”. Complete the lesson noting the diagrams and the bold terms. Click NEXT to go to “Other Multiple Mirror Systems”. Complete the lesson noting the diagrams, the italics terms, and complete the Check Your Understanding.

Analysis: Consider the following questions and submit your responses to your notebook.

1. State the law of reflection? 2. What are the characteristics of a virtual image? 3. What is a ray diagram? 4. For a reflection in a plane mirror, how does the object size and object distance compare to the image size and image distance? 5. Why does a plane mirror appear to reverse images left to right, but not top to bottom?

12.1.3 Web Walk – Reflections and Curved Mirrors Go to http://www.physicsclassroom.com/Class/refln/(The Physics Classroom – High School Physics Tutorial) Lesson 3: Concave Mirrors, “The Anatomy of a Curved Mirror”. Complete the lesson noting the diagrams, the bold red terms, and complete Check Your Understanding. Click NEXT to go to “Reflection of Light and Image Formation”. Complete the lesson noting the diagrams, the bold terms and the animations. Click NEXT to go to “Two Rules of Reflection for Concave Mirrors”. Complete the lesson noting the diagrams and guidelines for reflected light rays. What are the guidelines for constructing a ray diagram? Click NEXT to go to “Ray Diagrams – Concave Mirrors”. Complete the lesson noting the diagrams, the bold red terms, the animations and complete Check Your Understanding. What are the guidelines for constructing a ray diagram? Click NEXT to go to “Image Characteristics for Concave Mirrors”. Complete the lesson noting the diagrams, the bold red terms, the case examples and complete Check Your Understanding. Click NEXT to go to “The Mirror Equation”. Complete the lesson noting the equations and the sample problems. Complete the Check Your Understanding. What are the mirror equations? Click NEXT to go to “Spherical Aberration”. Complete the lesson noting the diagrams. How can spherical aberration be corrected?

Go to http://www.physicsclassroom.com/Class/refln/(The Physics Classroom – High School Physics Tutorial) Lesson 4: Convex Mirrors, “Reflection and Image Formation for Convex Mirrors”. Complete the lesson noting the diagrams and the rules of reflection for convex mirrors. Click NEXT to go to “Ray Diagrams – Convex Mirrors”. Complete the lesson noting the diagrams and examples. Do the practice ray diagrams.

Click NEXT to go to “Image Characteristics for Convex Mirrors”. Complete the lesson noting the diagrams and complete the Check Your Understanding. Click NEXT to go to “The Mirror Equation – Convex Mirrors”. Complete the lesson noting the equations and the sample problems. Complete the Check Your Understanding. What are the mirror equations? Are they the same for concave mirrors?

12.1.4 Lab Simulation – Reflections in a Plane Mirrorhttp://www.wfu.edu/physics/demolabs/demos/avimov/bychptr/chptr9_optics.htm Mirrors: Plane and Not so Simple

Analysis: Consider the following questions and submit your responses to your notebook.

1. What are the guidelines for constructing a ray diagram? 2. What are the mirror equations? 3. What is spherical aberration and how can it be corrected? 4. Compare and contrast the characteristics of virtual and real images in terms of orientation, location (position) relative to the mirror, size, and if it can be projected on a screen. 5. This statement “Objects may be closer than they appear.” is on the right hand outside mirror of your car. What is the significance of this warning?

12.1.5 Quick Lab – Refraction of Light

Go to online.cctt.org/physicslab/content/Phy1/lessonnotes/refractionoflight/refraction.asp (Online Physics Lab) Read and take notes.

Go to http://paer.rutgers.edu/pt3/experiment.php?topicid=12&exptid=181

12.1.6 Web Walk – Refraction, Snell's Law, and Internal Reflection

Go to http://www.physicsclassroom.com/Class/refrn/ (The Physics Classroom – High School Physics Tutorial) Lesson 1: Refraction at a Boundary “Boundary Behavior”. Complete the reading noting the diagrams and the animation. Click NEXT to go to “Refraction and Sight”. Complete the reading noting the diagrams, the bold terms and view the animation. Click NEXT to go to “Cause of Refraction”. Complete the activity noting the diagrams (analogies) and view the animation. Click NEXT to go to “Optical Density and light Speed”. Complete the reading noting the diagrams and table of indices of refraction. What is the relationship between optical density and index of refraction? How is the index of refraction determined?

Click NEXT to go to “The Direction of Bending”. Complete the reading noting the diagrams, the red bolded terms, the practice problem, and compete the Check Your Understanding. What is the “Least Time Principle”? Click NEXT to go to “The Secret of the Archer Fish”. Complete the reading noting the diagrams. What is the secret of the Archer Fish? Click Go to Lesson 2 (The Mathematics of Refraction). Complete “The Angle of Refraction” noting the diagrams and the bold red terms. Click NEXT to go to “Snell's Law”. Complete the activity noting the diagrams, the bold red terms, and the two example problems. Write a statement for Snell's Law. Click NEXT to go to “Ray Tracing and Problem Solving”. Complete the activity noting the diagrams, the bold terms, the example problems, and complete the Check Your Understanding. Write the equation for Snell's Law. Click NEXT to go to “Determination of n Values”. Complete the activity noting the diagrams, the bold terms, the sample data from a lab, and complete the Check Your Understanding. Click Go to Lesson 3 (Total Internal Reflection). Complete “Boundary Behavior Revisited” noting the diagrams and the bold red terms. Click NEXT to go to “Total Internal Reflection”. Complete the activity noting the diagrams, the bold red terms, and complete Check Your Understanding. Define critical angle. Click NEXT to go to “The Critical Angle”. Complete the activity noting the diagrams, the bold terms, the example problems, and complete the Check Your Understanding. How would you calculate critical angle?

Analysis: Consider the following questions and submit your responses to your notebook.

1. How is the index of refraction determined? 2. What is the secret of the Archer Fish? 3. Write a statement for Snell's Law. Write the equation for Snell's Law. 4. What is total internal reflection (TIR)? 5. Define critical angle. How would you calculate critical angle?

Knowledge Check

Now that you have an understanding of the law of reflection, consider this practical application of it. Some department store display windows are slanted inward at the bottom. The purpose of this is to reduce the glare (reflection) from brightly illuminated buildings across the street, which would make it difficult for shoppers to see the display. Prepare a sketch, to be shared and submitted to your instructor, of light rays reflecting from such a window to show how this technique works.

12.1.7 Quiz – Reflection and Refraction

Lesson 2: Lenses – To Diverge or to Converge!

Our view of the world of the world has been widened due to the discovery of lenses. When light shines through a lens, there is a bending of light as it enters and leaves glass or some other material. The light is refracted due to the shape and material of the lens and forms images of the object being viewed. The images formed can appear smaller, larger, closer, farther, upright, or inverted of the object being viewed. During this lesson you will apply the concept of refraction to lenses and pin holes. Some questions to ponder include: Why are there round, sometimes elliptical spots of light called sunballs beneath the trees on a sunny day? Why do you see better underwater when you wear goggles – after all it is not a lens?

12.2.1 Web Walk - Converging and Diverging Lenses

Go to http://www.physicsclassroom.com/Class/refrn/(The Physics Classroom - High Physics Tutorial) Lesson 5: Image Formation by Lenses “The Anatomy of a Lens”. Complete the activity studying the diagrams and the red bolded terms. (Note: The last diagram is incorrectly titled.) Click NEXT to go to “Refraction by Lenses”. Complete the reading noting the diagrams and the three rules (guidelines) for refraction through converging and diverging lenses.

Click NEXT to go to “Image Formation Revisited”. Complete the activity noting the diagrams and the comparison to mirrors. Click NEXT to go to “”Converging Lenses – Ray Diagrams”. Complete the reading noting the ray diagrams, image types, and image location. Click NEXT to go to “”Converging Lenses – Object-Image Relations”. Read each case paying careful attention to the bolded terms and diagrams. Complete the Check Your Understanding. Click NEXT to go to “”Diverging Lenses – Ray Diagrams”. Read each example paying careful attention to the terms and diagrams. Apply the three rules for ray diagrams for diverging lenses by doing the practice diagrams. Click NEXT to go to “”Diverging Lenses – Object-Image Relations”. Read each case paying careful attention to the terms and diagrams. Complete the Check Your Understanding. Click NEXT to go to “The Mathematics of Lenses”. Look at each sample problem paying careful attention to the red lens formulas and the solutions. Complete the Check Your Understanding.

Reflection: 1. Is a person who sees more clearly under water than in air without eyeglasses farsighted, nearsighted, or neither?

12.2.2 Quick Lab – A Lensless Lens!

Purpose: How can the diameter of the sun be calculated using the image created by a pinhole? Discussion: The image formed through a pinhole is in focus no matter where the object is located. In this activity, you use this concept to measure the diameter of the sun with a meter stick. The ratio of the diameter of the image to the distance from the pinhole is equal to the ratio of the diameter of the sun to its distance from the pinhole (150,000,000 km). Procedure: 1. Using a straight pin, poke a hole in an index card about 1.0 cm from the edge. 2. On a bright sunny day, hold the card in the sunlight and note circle of light on the ground. 3. Place a coin (penny, nickel, dime – your choice) over the image on the ground and adjust the position of the pinhole card until the image is the same size as the coin. (If the image is an ellipse, the short diameter should equal the diameter of the coin.) 4. Prepare a data table to record your collected data. Measure the distance from the pinhole card to the image on the ground. Measure the diameter of the coin and record the data. Collect data from different coins from other members in the class and record the data in your data table. 5. Hold the pinhole in front of your eye and read these directions through the pinhole. Bring the page closer to and closer to your eye until it is just a few centimeters away. You should be able to read the print clearly. Quickly take the pinhole away and see if you can still read the words.

Observations: (Data Table)

Calculations: 1. From the collected data, calculate the diameter of the sun in kilometers. 2. If the accepted value for the diameter of the sun is 1,400,000 km, determine your percentage of error.

Questions to ponder: 1. How close were your results to the accepted value? Were you impressed with the ease and accuracy of measuring the diameter of the sun using only a pinhole, a coin, and a meter stick? 2. Did the print appear magnified when observed through the pinhole lens? 3. Did the pinhole actually magnify the print? 4. Why was the print dimmer seen through the pinhole lens than seen using your eye alone? 5. A nearsighted person can see distant objects clearly through a pinhole. Explain how this is possible. (If you are nearsighted – try it!) Submit your report to your notebook.

12.2.3 Lab Activity – Images, Images and a Convex Lens!

Purpose: What is the nature, position, and size of images formed by a converging lens?

Discussion: The use of lenses to aid vision may have occurred as early as the 10 th century in China . Have you ever wondered how they work? What kind of lens corrects for nearsightedness? farsightedness? A lens refracts parallel rays of light so they cross – or appear to cross – at a focal point. A converging (convex) lens focuses parallel light rays to a focal point while a diverging lens (concave) spread light rays out. Converging lenses produce both virtual and real images depending on the position of the object. Review the types of images and their characteristics in your text.

Procedure: 1. Using a magnifying glass (convex lens), determine the focal length of the lens by having it convert a parallel beam of light from a distant object, such as a tree, to an inverted image on a screen, index card. (See the diagram below) ? ? | object lens screen 2. Measure the distance from the lens to the screen, focal length and record it in the data table. 3. Using a candle as the object, arrange a screen, convex lens, and object as shown in the diagram above. (A little piece of modeling clay will work as a lens holder.) Place the candle at a distance which is greater than the focal length (f) (Greater than 2f works well.) then move the screen until the image of the candle flame is as clear as possible. Measure the distance from the lens to the screen, image distance, and the distance from the lens to the object, object distance. Record the measurements in the data table. 4. Repeat Step 3 by positioning the lens at 1.5 focal lengths from the object. Record the measurements. 5. Repeat Step 3 by positioning the lens at 1 focal length from the object. Record the measurements. (Hint: see page 469 in your text.) 6. Repeat Step 3 by positioning the lens at 0.5 focal lengths from the object. (Hint: see page 468 in your text.) Record the measurements in the data table.data sheet 7. Complete the analysis and submit your findings to your notebook.

Analysis:

1. What relationship exists between the image distance and the object distance? 2. Compare virtual images to real images in terms of orientation, location, and position? 3. What type of a lens would be used to correct nearsightedness? farsightedness? 4. Construct a ray diagram to show the position, location, and size of the image formed in step 2. 5. Go to online.cctt.org/physicslab/content/applets/JavaPhysMath/java/clens/index.html and manipulate the applet for a review of image formation by a converging lens.Knowledge Check

Why is it when you are swimming underwater you can see much better if you wear goggles? A Central American fish, the Anableps, seems to have the best or perhaps the worst, of both media. It swims just beneath the water surface with its large eyeballs protruding above the water surface. Each eyeball is half in and half out of the water. Considering your need of goggles to see underwater, how can the Anableps see in both air and water this way? Respond to these questions in your notebook.

12.2.5 Quiz – Lenses

End Notes

Congratulations on the completion of another behavior of light. At this point in the study of the behavior of light you are able to see that converging lenses can be compared to concave mirrors, and diverging lenses can be compared to convex mirrors. Light rays pass through lenses but behave the same way as reflected rays do in mirrors. The mirror formulas can be applied to lenses as are the procedures for drawing ray diagrams. Nice job!

Lesson 3: Diffraction and Interference

Dazzling iridescent peacock feathers, soap bubbles, CDs/DVDs, rainbows, and the pearly luster of an abalone shell – what makes their fantastic colors? Have you ever stopped to look at soap bubbles? Did you notice that the swirl of colors changes as the soap bubble moved around? Have you noticed the iridescent sheen of some moth and/or butterfly wings and the flowing patches of color in an oil spill on the street after a rain shower? The beautiful colors were caused by interference, the way the reflections combined. Light reflected off the inner and outer surfaces of a thin film and interference produced the array of colors. To answer these questions and many more, we'll look into the mysteries of light and color due to interference, dispersion, and diffraction. By the end of this lesson you be able to explain why a soap bubble turns black just before it pops!

Check it Out!

The Students Alert for Physics Principles (SAPP) has received a call from Miss McGillivray saying that she had lost the specifications for her diffraction grating and must recalibrate it before she can perform the laser show at a school assembly. Although Miss McGillivray is a great presenter, she has little knowledge of the concepts diffraction and interference. SAPP has had such calls before and are ready to accept the challenge and save the show for Miss McGillivray. The SAPP group quickly rushes to the show site and recalibrates the grating using a 633 nm helium-neon laser to form 2 bright spots on a wall 4.0 m away that are each 1.40 m from the central bright spot. Now the show can go on thanks to SAPP! What is spacing between the grooves on the diffraction grating?

12.3.1 – Web Walk – Interference & Wave Behavior

It is important to go to the sites in order and follow the directions as given. If there is a related assignment, it will be clearly indicated. You may want to take notes as you move along the Web Walk. To take notes, open a new Word document and copy, paste, or type relevant information into that document. Save your document to your drive or disk. Taking notes electronically is good practice for this course, as well as good preparation for your future in higher education institutions.

Go to http://www.physicsclassroom.com/Class/light/(The Physics Classroom – High School Physics Tutorial) Lesson 1: How Do We Know Light Behaves as a Wave? “Wave Behaviors of Light”. Complete the reading reviewing reflection and refraction. Note the introduction of diffraction and interference the diagrams. Click NEXT to go to “Two Point Source Interference”. Complete the reading noting the bold red terms, the diagrams, the animations, and Young's Double Slit Experiment.

Go to http://www.physicsclassroom.com/Class/light/(The Physics Classroom – High School Physics Tutorial) “2 Point Source Interference Patterns – Changing Separation Distance” and look at the animation of 2-point source interference patterns. What are nodes and anti-nodes? Scroll down and click on “Interference of Waves”. Note the bold red terms, the diagrams, and complete Check Your Understanding.

Analysis: Consider the following questions and submit your responses to your instructor.

1. What is the principle of superposition? 2. Stars are point sources of light; however, we see them and draw them with pointed spikes. What is a possible explanation for this phenomenon? 3. Why is it important that monochromatic light be used in Young's interference experiment? 4. What produces the series of light and dark lines (spots) when monochromatic light passes through a diffraction grating? The bright lines are caused by what behavior of light? The dark regions are caused by what behavior of light?

12.3.2 Quick Lab – Rainbows, Bubbles, and More!

Purpose: How do we get rainbow colors without rain?

Discussion: Rainbows are produced by the refraction and the refection of light from drops of water in the sky. Rainbow colors can be produced in a variety of ways. We will explore some of these ways in this activity and have some fun! Procedure: 1. Dip the bubble making wand into the bubble solution. Hold the wand in a vertical position and look at the soap film with the room lights behind you (reflecting off the film). List as many observations as you can of what you saw with the soap film. How would you explain the observations? 2. Blow some bubbles and observe the colors of the bubbles. Try changing the size of the bubbles by blowing slowly. Pay careful attention to the color changes in the bubbles especially just before they pop! List as many observations as you can of what you saw with the soap bubbles. Why do soap bubbles display so many different colors? 3. During or after a rainfall, you may have noticed the brilliant colors on a wet roadway or parking lot where oil has dripped from a car. To reproduce this situation, look at figure 31.23 on page 491 in the text. List as many observations as you can of what you saw with the gasoline on the street. How would you explain the observations? 4. Place two glass plates or microscope slides together and try to observe the colored bands by holding the glass plates in front of you and moving them so they are reflecting light from the ceiling lights. Be patient as you move the glass

plates around – you will see rings of color when you them in the right position. (Sometimes a piece of hair between the slides helps.) List as many observations as you can of what you saw with the glass plates. How would you explain the observations?

Observations:

Reflection:

1. Why does a soap bubble turn black just before it pops?

Knowledge Check

There is a colorful but mysterious haze that appears over wooded areas that are free from manmade contamination. The Blue Ridge Mountains of Tennessee and the Blue Mountains of Australia are both well known for their beautiful blue haze. What causes this blue haze? Smoke? No, because the blue haze is found in relatively uninhabited areas. Windswept dust? No, because the haze has the deepest blue during very light winds. The haze can not be fog because the blue is most common during warm summers. What then is the cause of the haze and why is it blue? Respond to this question and submit the answer to your notebook.

End Notes

Wow! You have just added to your knowledge base about the behavior of light. The mysteries of light and color due to interference, reflection, dispersion, and diffraction and relatively easy to explain now that you have completed this lesson. The beautiful colors you saw were caused by interference of waves, the way the reflections combined. With the bubbles and the gasoline spill, light reflected off the inner and outer surfaces of a thin film and interference produced the brilliant array of colors. Now you can explain why bubbles turn “black' just before they pop! Good job!Lesson 4: Unit Wrap Up – Behavior of Light Exam

Written and Practical

1. Make a maze out of the cardboard pieces or use books to make the walls. Put the laser pointer at one point in the maze, and the folded paper at another (so the beam can’t reach the paper).

2. Criteria your beam must meet before it hits the paper.Separate into 2 beamsOne beam needs to go over the walls (ht.=6 in)One beam needs to go around the walls and through a glass of water.The two beams need to meet and hit the paper as one.

An example of how the maze can look

laser

Walls