Exploring Light and Color

Transcription

1 Exploring Light and Color From The Basics of Physics Series Unit of Study INSTRUCTOR S GUIDE

2 EXPLORING LIGHT AND COLOR From The Basics of Physics Series A Unit of Study Instructor s Guide Produced by Colgren Communications Written by John Colgren United Learning 1560 Sherman Avenue, Suite 100 Evanston, Illinois (800) , Fax (847)

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4 EXPLORING LIGHT AND COLOR From The Basics of Physics Series Introduction... 1 Instructional Notes... 1 Links to Curriculum Standards... 2 Student Objectives... 3 Assessment Tools... 3 Teacher Preparation... 4 Introducing the Program... 4 View the Program... 4 Discussion Questions... 4 Blackline Master Descriptions... 5 Enrichment Activities... 6 Answer Key... 7 Internet Resources Script of Presentation CC This video is closed captioned. The purchase of this video program entitles the user to the right to reproduce or duplicate, in whole or in part, this teacher s guide and the blackline master handouts that accompany it for the purpose of teaching in conjunction with this video, Magnetism. This right is restricted only for use with this program. Any reproduction or duplication in whole or in part of this guide and the blackline master handouts for any purpose other than for use with this program is prohibited.

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7 EXPLORING LIGHT AND COLOR From The Basics of Physics Series Grade Levels: 5-8 INTRODUCTION This live-action program is designed for use with the intermediate grade levels (5-8). This program is about light and color. Light is an important part of everyone s daily life. We depend on light in so many different ways. This program will explore the properties and nature of light and color. It will discuss how the eye works, how different animals see, reflection, refraction, the speed of light, fiber optics, and laser technology. The properties of light are demonstrated through experiments and simple demonstrations. INSTRUCTIONAL NOTES Before presenting this lesson to your students, we suggest that you preview the program and review this guide and the accompanying blackline master activities in order to familiarize yourself with their content. As you review the materials presented in this guide, you may find it necessary to make some changes, additions, or deletions to meet the specific needs of your class. We encourage you to do so, for only by tailoring this program to your class will they obtain the maximum instructional benefits afforded by the materials. It is also suggested that the program presentation take place before the entire group under your supervision. The lesson activities grow out of the context of the program; therefore, the presentation should be a common experience for all students. 1

8 LINKS TO CURRICULUM STANDARDS This Unit of Study addresses the following National Science Education Standards for grades 5-8: Science as Inquiry Content Standard A: Abilities necessary to do scientific inquiry Plan and conduct simple investigations. Employ simple equipment and tools to gather data. Use data to construct a reasonable explanation. Communicate investigations and explanations. Understanding about scientific inquiry Physical Science Content Standard B: Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways. Science and Technology Content Standard E: Abilities of technological design Understanding about science and technology People have always had questions about their world. Science is one way of answering questions and explaining the natural world. People have always had problems and invented tools and techniques to solve problems. Scientists and engineers often work in teams. Tools help scientists make better observations, measurements, and equipment for investigations. History and Nature of Science Content Standard G: Science as a human endeavor Science and technology have been practiced for a long time. Men and women have made a variety of contributions throughout the history of science and technology. Although men and women using scientific inquiry have learned much about the objects, events, and phenomena in nature, much 2

9 more remains to be understood. Science will never be finished. Many people choose science as a career and devote their entire lives to studying it. STUDENT OBJECTIVES After viewing the video and participating in the lesson activities, the students should be able to do the following: Define terms such as reflection and refraction. Recognize the colors of the spectrum. Identify the primary colors of light. Identify Newton as an important contributor to our knowledge about light and color. Identify the sun as the most important source of light energy to the earth. Describe how the human eye operates. Describe how convex and concave lenses are different from one another. Describe how light reflects off flat, concave, and convex mirrors. Describe how color is absorbed and reflected by different objects. ASSESSMENT TOOLS This lesson provides you with three different assessment tools. Together they make it possible to follow closely the progress of your students and to judge their mastery of the subject matter. The Pre-Test (Blackline Master 1) can be used to get some idea of students understanding of the topic before the program is presented. The Post-Test (Blackline Master 20) can be used as a final test for the lesson. 3

10 The Program Quiz and its accompanying answer sheet (Blackline Master 2) can be used either as a way to introduce the topic prior to showing the program or to judge student mastery once the program has been presented. TEACHER PREPARATION View the program and review the accompanying activities. Duplicate any blackline masters you wish to distribute. If you plan to use the Program Quiz, which immediately follows the program presentation, you may wish to have copies of the quiz ready to distribute at the completion of the program. Also, plan to pause the tape between questions if students require more time. INTRODUCING THE PROGRAM Ask the students to identify the five major senses that humans use to gather information about their world. (sight, touch, hearing, smelling, and tasting) Of those five senses which is responsible for collecting information which one is the stand out leader. Sight is our most important way to gather information about the world around us. Light and color are essential to our lives. Ideas about how our eyes work and how objects produce and reflect light have changed over the years. This program will describe how important light is and how it works. VIEW THE PROGRAM Viewing time for this program is 15 minutes. The program quiz that follows the presentation will take about three minutes when you build in pauses for recording answers. DISCUSSION QUESTIONS You may wish to conduct a discussion after viewing the program based on the following: 4

11 1. Ask students to consider how we use light to go about our daily routines. 2. Review how reflected light is responsible for the colors we see. 3. Describe how fiber optics is being used in communications and medicine. BLACKLINE MASTER DESCRIPTIONS This program contains twenty blackline masters that can be used to reinforce ideas and information presented in the program. Blackline Master 1, Pre-test, provides a way of finding out how much students know about the material covered in this lesson before you present it. Student scores on the Pre- Test can be compared with their scores on the final Post- Test (Blackline Master 20). Blackline Master 2, Program Quiz, is to be used at the end of the program. At the completion of the program, there is a short quiz. The narrator will read the questions which are displayed on the screen. Students can use Blackline Master 2 to record their answers. Answers to the questions are provided in the Answer Key section of this instructor s guide. Blackline Master 3, How Does Light Travel?, is an experiment to demonstrate how light travels. Blackline Master 4, Pinhole Scope, is an experiment demonstrating a method for building a pinhole scope. Blackline Master 5, Reflections Inside Water, is an experiment for examining the reflection of light in a water stream. Blackline Master 6, Kaleidoscope, is an experiment for building a homemade kaleidoscope. Blackline Master 7, Mixing Colors with Light, is an experiment to demonstrate how mixing colored light can make different colors. Blackline Master 8, Making Dyes,is an experiment for making different colored dyes using vegetables and fruits. 5

12 Blackline Master 9, Chromotography, is an experiment designed to determine the pigments used in colored pens and inks. Blackline Master 10, Water Drop Lens, is an experiment designed to demonstrate the magnifying ability of a water lens. The first magnifying glasses used water drops. Blackline Masters 11 and 12, The Angle of Incidence Compared to the Angle of Reflections, is an experiment for comparing the angle of incidence (the angle at which light strikes a mirror) with the angle of the reflected light. Blackline Master 13, Mirror Maze, is an experiment for testing your ability to move a pencil point through a mirror image of a maze. Blackline Master 14, Homemade Periscope, is an experiment to build a periscope for looking over walls or around the corner. Blackline Master 15, Spectroscope, is an experiment for building a homemade spectroscope. Blackline Master 16, The Human Eye, is an information sheet about nearsightedness and farsightedness. Blackline Master 17, Blind Spot, is an experiment for demonstrating the human blind spot. Blackline Master 18, Persistence of Vision, is an experiment for illustrating the concept of persistence of vision. Blackline Master 19, Optical Illusions, is a worksheet challenging students to identify answers about optical illusions. Blackline Master 20, Quiz,is an evaluation tool for this unit. ENRICHMENT ACTIVITIES 1. Have some students find out about the use of light by scientists to determine the distance of stars. Find out about the red blue shift of star light. 6

13 2. The light-year is a measurement used indicate the distances between the stars and galaxies. These distances are so huge that a very large unit of measurement is needed. Have the students determine what a light-year equals. The term is defined as the distance light travels in one year. The speed of light is 186,000 miles per second. So to determine the distance light travels in one year we must multiply the number of seconds in a year by 186,000. Provide the students with the definition for a light-year and then help them figure out that they will have to determine the number of seconds in a year and multiply that times 186,000. Give this as a homework challenge. The answer is rounded off to 6,000,000,000,000 miles (six trillion). To demonstrate how huge the universe is explain that the closest star to us other than our sun is four and a half light-years away. That is 26,000,000,000,000 miles. It would take light 4.5 years to reach us from that star. ANSWER KEY Blackline Master 1, Pre-Test A. 1. Photosynthesis is the food making process cared on by plants. 2. The retina is found at the back of the eye and is the area of the eye containing rods and cones. Images we see fall on the retina and allow us to see. 3. The visible spectrum is a very small part of the electromagnet spectrum. The visible spectrum is the only section of the em spectrum that humans can see. 4. The optic nerve carries signals from the retina to the brain where the information is interpreted. 5. Ultraviolet light is found just above violet on the em spectrum. Ultraviolet light is damaging to the skin. 6. Infrared light is found just below red. 7

14 7. ROY G BIV is a method for remembering the primary colors of light. It stands for red, orange, yellow, green, blue, indigo, and violet. 8. Fiber optics is the use of plastic or glass tubes to direct a concentrated beam of light. The fiber optic material allows the light to bend. B. Short Answer 1. Binocular vision allows us to determine the distance of objects. The eyes are positioned on the head in such a way as both eyes work together to view our world. 2. Fish and birds have their eyes on the side of their heads to allow for a greater field of vision. This helps the animals see other animals sneaking up on them. 3. White light strikes an object and some colors are absorbed and some are reflected. It is the reflected light that we see. 4. The primary colors of light are red, green and blue. All other colors can be made from overlapping variations of these colors. 5. A prism is used to divide white light into the colors of the spectrum. 6. Light travels at 186,000 miles per second or 300,000 kilometers per second. 7. Refraction is the bending of light when it moves from one medium into another. Light travels at different speeds in different substances. 8. Transparent materials allow light to go through them easily. We can see through transparent materials. Translucent materials hinder our view. Light doesn t travel through them smoothly. Opaque materials are solid materials that allow no light to go through them. 9. Persistence of vision is responsible for our ability to see motion in things such as simple drawings in a flip book. 10. Convex lenses are thick in the middle and thin on the edges. Concave lenses are narrow in the middle and thick at the edges. 8

15 Blackline Master 2, Program Quiz 1. The lemon will appear dark because there is no yellow light to be reflected. 2. The primary colors of light are red, green and blue. 3. Red, orange, yellow, green, blue, indigo, and violet. 4. Black colors absorb all the white light while white objects reflect all the colors. The absorbed colors add heat to the object. 5. Light bends when moving from one medium into another. 6. Concave mirrors magnify things while convex mirrors make things appear smaller We see the colors that are reflected by objects. The other colors are absorbed by the object. Blackline Master 3, How Does Light Travel? Observations: 1. The light goes through all three holes. 2. When the center card is moved, the light only goes through the first card and hits the center card. Conclusion: Light travels in a straight line, so when the cards aren t lined up, the light can t get through. Blackline Master 4, Pinhole Scope Conclusions: The image is upside down for the same reason that the image is upside down at the back of the eye. Blackline Master 5, Reflections Inside Water Conclusion: The light bends in water because it slows down in water and is refracted with the water. Blackline Master 6, Kaleidoscope 9

16 This design won t work as well as store bought versions, but it is still worth building. Blackline Master 7, Mixing Colors With Light It might be difficult to get the kind of filter that works best. Try companies that supply theaters with light gels. Blackline Master 8, Making Dyes Some very vivid dyes can be made with vegetables and berries. Blackline Master 9, Chromotography Observations: 1. The ink begins to travel with the water and the pigments that make up the ink start to separate. 2. The colors separate because of weight. The heaviest pigments separate first, and lightest pigments continue to travel with the water up the paper. Blackline Master 10, Water Drop Lens Observations: 1. The small drops magnify the best The small drops are convex shaped. Conclusions: The small drops work like convex lenses and magnify things well. Blackline Masters 11 and 12, The Angle of Incidence Compared to the Angle of Reflections Observations: 1. The angles are the same. 2. The results should be the same. The angles are the same. Conclusions: The angle of incidence is the same as the angle of reflection. Blackline Master 13, Mirror Maze Observations: 1. Times will vary. 10

17 2. Results will vary. Conclusions: This activity is difficult because a flat mirror reflects things in reverse. Blackline Master 14, Homemade Periscope The image will not be reversed because it is reflected into two mirrors causing the image to right itself. Blackline Master 15, Spectroscope Students should see the spectrum with black lines or areas depending on the light source. Blackline Master 16, The Human Eye This is an information sheet. Blackline Master 17, Blind Spot Students should see that the circle disappears and then reappears as the card is brought closer to their face. Blackline Master 18, Persistence of Vision Drawings will vary. Blackline Master 19, Optical Illusions 1. both lines are the same length. 2. The height and width of the hat is the same. 3. They are the same size. 4. There is an extra the in the phrase 5. B Blackline Master 20, Post Test 1. Light travels at the incredible speed of 186,000 miles per second. 2. Birds and fish have eyes on the sides of their heads so they can have a wider field of vision. This helps them to spot animals sneaking up on them from the sides and from behind. 3. Our eyes retain an image for a brief time after the image is gone from view. This is how movies work. They are actually made up of many still pictures and when shown quickly one after another they give the impression of motion. 4. The primary colors of light are red, green and blue. 11

18 5. Photosynthesis is the food-making process of plants. Plants use carbon dioxide from the air, minerals and water from the ground and sunlight to make glucose a form of sugar. 6. The view that we see from our right eye is slightly different from the view of our left eye. This is what gives us three dimensional vision and an ability to estimate distances. 7. a. Opaque means that no light can go through. Opaque objects are solid. b. Transparent means that we can see clearly through the object. c. Translucent means that are view isn t clear looking through an object. d. The optic nerve carries signals from the cones and rods of the retina to the brain. e. The retina is made up of cones and rods which are capable of differentiating colors and sights. It is located at the back of the eye. f. The cornea is a protective clear section of the eye that covers the iris and pupil. The cornea focuses light as it enters the eye. g. The iris is the colored part of the eye. The iris opens and closes to adjust the amount of light entering the eye. h. The pupil is the dark hole in the center of the iris. i. The blind spot is the part of the retina where the rods and cones come together to form the optic nerve. Because there are no rods or cones at this point no images can be seen. INTERNET RESOURCES The following websites may be valuable sources of additional information to reinforce the objectives of this lesson: 1. A very sophisticated site intended for advanced exploration and use by high school and college students. However, more capable students may benefit from the elaborate java interactives and content. 12

19 2. Sponsored by the Franklin Institute Online The Formal Education Group of the Space Telescope Science Institute Office of Public Outreach. Classroom resources based on the Hubble Space Telescope s greatest discoveries. A visually appealing educational site Tech Museum of Innovation and Adobe Systems Incorporated x.html The Annerberg/CPB Math and Science Project Interactive site with a very good activity on stellar spectrum. This shows how astronomers can look at starlight and determine what the star is made of. Script of Program Narration EXPLORING LIGHT AND COLOR The world is filled with bright and colorful things, from beautiful flowers to tropical fish to breathtaking butterflies. Just take a moment to look around at the wide variety of colors that surround us, wherever we are. The zoo, a canyon, a clothes closet - they all abound with color. That's why our sense of vision is often considered our most important sense. We collect nine-tenths of our information about the world around us through our sense of sight. Hearing, taste, smell, and touch are important senses, but when it comes to gathering information, our sense of sight is the most important. Light is the key to our whole sense of sight. 13

20 THE SUN, LIGHT, AND PHOTOSYNTHESIS The key source of light on earth is the sun. Even ancient people realized the importance of light, and they worshipped the sun to try to ensure that the supply of light would not run out. All living things on the planet depend on light. The light from the sun provides energy and heat. Green plants use light in their food-making process called photosynthesis. During photosynthesis, carbon dioxide, which is exhaled by animals, and minerals and water, which are absorbed by the plant from the earth, are combined in the presence of light to make glucose, a kind of sugar, for the plant to use for its own growth and survival. The plant gives off oxygen as a by-product of this food-making process. All animals, including humans need oxygen. Plants can't live without light. If a green plant doesn't receive light, it will not be able to make food and will eventually die. If plants were to disappear from our planet, animals would soon follow. Many animals eat plants and all animals breathe the oxygen that only plants can produce. So, all life on earth is dependent upon light from the sun. THE SENSE OF SIGHT People have always been fascinated with light and the sense of sight. But not all the ideas about light and sight have been correct. For instance, about 2,000 years ago, the Greeks thought that eyes worked because they sent out energy that hit an object and bounced back. They thought this because they observed the eyes of animals such as cats, dogs and deer in the dark. Their eyes appeared to glow. It was this glow that made them think that the eyes were generating a light energy. Actually, cats, dogs, and deer can see better in the dark than we can because their eyes can open up further to collect as much available light as possible. 14

21 However, nothing can see in total darkness because all eyes need an outside light source to work. We now know that eyes make it possible for animals and humans to see because of reflected light. This is how reflected light works: Light strikes an object and bounces off, or reflects. The reflected light enters our eye and an image of what we see is formed on the back of the eye, called the retina. The retina is made up of rods and cones that are sensitive to light. The rods are sensitive to light and dark, but not color. The cones are capable of sensing different colors. Primates, including humans, are the only mammals to experience full color vision. Dogs, cats, mice, rabbits, and most mammals see a black and white world because their eyes lack color sensing cones. There are other animals that can see color, but usually not all the colors we see. Usually animals that look colorful can see in color. For instance, birds and butterflies can see in color. Scientists have found color sensing cones in the eyes of birds and butterflies. Even snakes and lizards can see colors. The bright colors and markings of many animals help them to identify each other. Many birds and fish have their eyes on the side of their head, so that their field of vision is larger. This helps them to see things that might be approaching them from different directions. Insects have compound eyes, which are made up of thousands of lenses. This is a close-up of a bee's eye. THE HUMAN EYE As you can see in this diagram, the human eye is very complicated. Light enters the eye through the pupil, which is the dark hole in the center of the iris. The iris is muscle tissue, which determines the size of the pupil. In bright light, the iris closes the pupil, so not as much light gets in. 15

22 Under dark conditions, the iris opens up the pupil, allowing greater amounts of available light to enter the eye. The iris is the blue, green, brown, or hazel part of the eye. The white part of the eyeball is a tough protective skin. It covers the entire eyeball except for the clear area over the iris and pupil. This protective clear section is called the cornea. The cornea bends the light towards the lens. The cornea focuses the light entering the eye. Most people think that the lens is responsible for focusing, but that is wrong. The lens helps us to be able to focus on things that are close, as well as things that are far away. The lens is adjusted when small muscles change the shape of the lens. However, it is the cornea that does the most to focus light that enters the eye. Light enters the cornea and then is bent towards the retina, where an inverted image strikes the rods and cones. The rods and cones send electrical impulses to the brain through nerve fibers that collect to form the optic nerve behind the eye. The place where the fibers come together has no rods or cones, so images can't be seen at this point. This spot is referred to as the blind spot. The optic nerve carries the information to the brain where it is turned rightside-up and analyzed. Humans have two eyes for a purpose. We have what is called binocular vision. The image from each eye is combined to give us the ability to determine distance. The field of vision is determined by how much you can see without moving your head. HOW IS LIGHT PRODUCED? To understand how light is produced we need to think at the atomic level. Orbiting the center or nucleus of an atom are the electrons. The electrons orbit at certain distances from the nucleus. If an electron gains energy it can jump or move to a higher orbit. But it 16

23 doesn t stay at this new position long and moves back to its original orbit. When this happens the electron releases the energy it had absorbed. This energy is released as a photon. This photon or particle of light is the energy released when the electron moves back to a lower energy level or orbit. So it is the movement of electrons back and forth between energy levels that produces the photons of light. If we turn on a light, electrical energy goes into the filament of the bulb. This causes the atoms in the filament to vibrate. Energy causes the electrons of those atoms to move back and forth to different energy levels producing photons of energy, which we see as light. A stream of photons travels as waves of vibrating electric and magnetic fields. A field can exert a force on another object without touching that object. A force is a push or a pull. Think of a magnet interacting with a paper clip. The paper clip is pulled towards the magnet without touching. The vibrating electric and magnetic fields make light apart of the electromagnetic spectrum. These waves can travel through the emptiness of space as a form of radiation. They travel as invisible transverse waves. Visible light only makes up a very small part of the electromagnetic spectrum. Light travels as waves. Light also behaves like a particle. Because light appears to have the properties of both particles and waves, scientists refer to it as the particle-wave theory of light. REFRACTED LIGHT Isaac Newton, in 1665, made some important discoveries about light and color. He found that white light entering a glass prism could be bent and separated, or refracted, into seven color groups. These principal color groups were red, orange, yellow, green, blue, indigo, and violet. To remember the order of these colors, think of their first letters to form the name ROY G BIV. 17

24 Newton conducted other experiments and found that all seven refracted colors could be bent again, with a second prism, back to make white. We call the collection of these seven colors of which white light is composed the visible spectrum. The colors bend at different angles because the colors each travel at different speeds. Violet is bent the most because it travels slower than the other colors when it goes through glass or water; light travels slower through water and glass than it does through air, so it s easier to see this effect when we use them. Red bends the least because it travels faster than the other colors. All the colors have their own speeds. We don't need a glass prism to break light into its spectrum. In fact, nature can provide us with a beautiful spectrum in the form of a rainbow. Rainbows occur when sunlight is refracted in small droplets of water. The raindrops act like little water prisms that refract the light and form a rainbow. THE ELECTROMAGNETIC SPECTRUM Light is a form of radiation given off by the sun. It is part of the electromagnetic spectrum. Actually, it is a very small part of the spectrum, as you can see in this chart. Humans can only see the section called the visible spectrum. The other forms of radiation are invisible to us, but they are still there. The rays of different types of radiation have different wavelengths, just like the different colors of the spectrum have different wavelengths that cause them to separate into the color spectrum. 18

25 Radio waves, with the longest wavelengths, are at the end of the spectrum. All television and radio stations broadcast radio waves. Sounds and pictures are changed to electrical signals, which are transmitted by radio waves over great distances and then received by a radio or television and converted back to electric current and sounds and pictures. Microwaves are the next set of waves on the electromagnetic spectrum. A microwave oven generates microwaves, which penetrate food and cause the water molecules in the food to vibrate. The vibration of the water molecules causes the temperature of the food to rise. Radar also uses microwaves. For instance, a radar gun used by the police sends out a quick burst of microwaves that reflect off a car and return to the gun. The speed of the car can then be determined. Two more types of radiation given off by the sun that we can t see are ultraviolet and infrared. Infrared is found before the visible spectrum just before red. Infrared energy is heat energy. You feel infrared energy at the beach when you sit in the sunlight. Infrared waves from the sun are absorbed by your skin. We can t see infrared waves, but there are devices that can be used to detect this energy. Brighter colors indicate areas of higher temperature. Ultraviolet waves are just beyond violet on the electromagnetic spectrum. 19

26 These rays can be very damaging to the skin and can even cause skin cancer. That's why it's not a good idea to sit out in the sun without a strong sunblock. X-rays are next in the electromagnetic spectrum. They are used in various ways in the medical field. Because the rays penetrate many materials easily, they are used to examine broken bones and to check your teeth. X-rays are not harmful unless you are exposed to too many of them, so patients are usually draped in a lead apron to protect areas of the body not being X-rayed. So visible light is actually only a very small portion of the electromagnetic spectrum. There are a lot of energy waves that are beyond our ability to see. That doesn t mean they re not there. Experiments have shown that flowers under ultraviolet light have a totally different appearance than what we see. Bees and other insects probably see these flowers as they appear in the ultraviolet spectrum. REFLECTED LIGHT Isaac Newton's work helped to explain why things have different colors. When we see a nice red apple, it's because the apple is reflecting red light waves and absorbing all the other colors. The white light that strikes the apple contains all the colors, including red. All the other colors are absorbed, and the red bounces off the apple and enters our eyes. The colors we see are the colors reflected by objects. If we light an object with something other than white light, we will get different results. Here is the nice red apple; if we shine a green 20

27 light on the apple, it will not appear red. It appears black. This is because the green light has no red in it. The green is absorbed, so the apple looks black because it is reflecting no colors. White objects reflect all the colors, whereas black reflects no colors. It absorbs all the colors of light. PRIMARY COLORS OF LIGHT We can mix different colors of light to make other colors. There are three colors of light that can make the other colors of the spectrum. These colors are called the primary colors of light. They are red, green, and blue. Here is a white paper plate. When we shine red light on it, it appears red. When we shine a green light on it, it looks green, and if we combine the red and green light, it appears yellow. If you look closely at a color television screen, you will see that the entire screen is made up of hundreds of dots arranged in groups of three. There are tiny red, green, and blue dots that can be used to create all the colors you see on television. Don't confuse the three primary colors of light with the three primary colors of pigments. Pigments reflect different colors and are used in paints and dyes. Pigments may be combined to form different colors, and often, an object contains more than one pigment. Mixing pigments is not the same as mixing the primary colors of light. The primary colors of pigments are red, blue, and yellow. Color photographs are made up of these three pigments. THE NATURE OF LIGHT If you shine a flashlight across the room, you'll see that the light travels straight. It doesn't bend around corners. You may also notice that the light travels fast, very fast. In fact, light is the fastest thing of which we know. It travels faster than a car, faster 21

28 than the wind, even faster than a jet plane. Light travels at the incredible speed of 186,000 miles, or 300,000 kilometers, per second. That's like traveling from New York to San Francisco 62 times in one second. Nothing but light can travel at that speed. Light travels at different speeds through different substances. In the emptiness of space, where there are no gases, light travels at its maximum speed. In air, glass, or water, light travels more slowly. Normally, light travels in a straight line, but when it goes from one substance to another, it may change direction because it slows down or speeds up. This change in speed causes the light to bend, or, as scientists call it, refract. We can demonstrate refraction in a variety of ways. If we look at this pencil in the glass of water, it appears that the pencil is bent. When this bird is fishing, it must take into consideration the fact that the fish is not where it appears to be, because the reflected light from the fish bends when it moves from the water to the air. If the bird didn't know this, it would always be striking in the wrong place. FIBER OPTICS Fiber optics is a technology that is used in a number of interesting ways. The fiber optic material is flexible glass or plastic that can be as thin as a human hair. Light that goes in one end of the fiber is reflected, back and forth, from side to side, the entire length of the fiber. The fiber can be twisted and bent and the light still comes out the other end. Fiber optics is used to send telephone calls because more information can be carried than with electric cables. It is also used to videotape in hard-to-reach places, such as parts of the human body reached during surgery. Fiber optic material is used for lamps and even sold as a fun flashlight toy. LASER LIGHT Laser light is a human-made light composed of only one kind of wavelength. Laser light can be used in a variety of ways because of its special properties. It is used at the library and at stores to read 22

29 bar codes to identify products. The laser is used in operations because it can cut more accurately than a scalpel and because there is less bleeding when laser surgery is performed. Lasers can be used to cut sheets of metal. Your CD player uses a laser to read the signal from the disc. The light from the laser doesn't wear down the disc, so the sound quality is always excellent. Holograms are made with laser light. The hologram looks threedimensional, and as you turn from side to side, the image changes. TRANSPARENT, TRANSLUCENT, AND OPAQUE When light strikes an object that is transparent, the light goes through. Glass and clear plastic are transparent. Translucent materials are materials that let some of the light through, but the translucent materials scatter the light, so that it is hard to see clearly what is on the other side. Most objects are opaque, which means they do not allow any light to go through them. Here's an interesting demonstration. We'll use a slide projector and a dowel rod. First, we find the point where the image is focused. The white poster board will locate that spot. Then the poster board is put aside and the image disappears. Now, when we wave the dowel rod quickly back and forth, the image reappears. The image is there the whole time, but we can only see it when there is something to reflect it to our eyes. The dowel rod creates that service and the persistence of vision lets us see the whole image, even though the reflected light comes to us in pieces. Persistence of vision helps us see this stickman, made up of separate pictures, walk. Our eyes retain, or hold on to, each image for a fraction of a second, so we see the image on the slide and the man walking. MIRRORS AND LENSES 23

30 Some objects, like mirrors, reflect all the light that strikes them. The image in a flat mirror is reversed. See how the letters are reversed? Some mirrors are curved either inward or outward. A mirror that curves inward is called a concave mirror. The image in a concave mirror looks upside down, unless you are very close to the mirror. This make-up mirror is designed to be used close-up. A mirror that is curved outward is called a convex mirror. The image is right side up. Notice with a convex mirror, you can see more of what is around you. Convex mirrors are often used on cars to help a driver see if there are any other cars nearby. Amusement parks use special mirrors that are part convex and part concave to create interesting results. Images can be greatly altered by mirrors. Lenses are made of transparent material like glass or plastic. They are designed to make objects appear larger or smaller. There are two kinds of lenses. Lenses that curve inward are called concave, and those that curve outwards are convex. Concave lenses are thin in the middle and thicker at the edges. These lenses bend light outwards. Convex lenses are thick in the middle and thin on the edges. Convex lenses magnify objects. Lenses are used to help correct vision problems. Our eyes see things clearly only when the image falls on the retina. If the focal point is in front of the retina, or behind the retina, things will appear blurry. Nearsightedness is corrected with concave lenses that move the focal point further back, to the eye's retina. Farsightedness is corrected with convex lenses that move the focal point forward. Lenses are also used in microscopes and telescopes. The first microscope used a small water drop to bend the light and magnify it. Now microscopes use a series of glass lenses to magnify things we can't see with just our eyes. Look at these microscopic single-cell animals found in pond water. Telescopes are used to study outer space. With telescopes, we have found out a great deal about planets and stars. Light, reflected from planets or given off by stars, can enter a telescope and be magnified to provide us with clear details of the object being 24

31 observed. Stars, such as our sun, generate light, but planets and moons don't produce their own light. They reflect the light given off by the sun. THE LIGHT BULB Back in 1879, Thomas Edison demonstrated a new form of light generated by an electric light bulb. Though he didn t invent the light bulb, he did produce the first practical bulb. The wire inside the bulb is very thin, and when electricity flows through the wire, it heats up and gives off light. The bulb part, which is made of clear glass, has had the air removed so the filament won t burn out quickly. This is called an incandescent light. It glows because electricity heats up the small wire called a filament. Fluorescent lamps work a little differently, as they are filled with a gas that gives off ultraviolet light when electricity passes through it. This ultraviolet light causes a phosphorescent coating on the inside of the tube to glow. VIDEO QUIZ Now it is time for the program quiz. There are eight questions you can answer on the program worksheet or on a separate sheet of paper. Question 1: If we shine a green light on this lemon, what color will the lemon appear? Question 2: What are the primary colors of light? Question 3: What are the seven color groups in the light spectrum? Question 4: Why do black objects absorb more heat energy than white or colored objects? 25

32 Question 5: Why does light refract or bend when it travels through glass or water? Question 6: Describe how concave and convex mirrors are different from one another. Question 7: Draw arrows on the concave and convex lenses to show how light moves through them. Question 8: How do we see color from objects bathed in white light? 26