Lesson 2: How Does Light Reflect? PDF

LESSON 2 How Does Light Reflect? Even astronauts take selfies! All visible light bounces off certain surfaces, such as mirrors. Light bouncing into our eyes allows us to read these words. © Houg...

LESSON 2 How Does Light Reflect? Even astronauts take selfies! All visible light bounces off certain surfaces, such as mirrors. Light bouncing into our eyes allows us to read these words. © Houghton Mifflin Harcourt By the end of this lesson... you’ll be able to explain how light interacts with different surfaces and why people can see the things they do. 170  Explore Can You Explain It? Online Telescopes like this one can be used to capture light from objects in space. This nebula, which is a cloud of dust and gases, is millions of kilometers from Earth. So how can we see it? 1. How does a telescope allow us to see things that are millions of Tip kilometers away from us? Learn more about waves in What Are © Houghton Mifflin Harcourt Image Credits: (l) ©David Parker/Science Source; Waves? and how energy transfers through waves in How Is Energy Transferred? (r) ©Science Source EVIDENCE NOTEBOOK Look for this icon to help you gather evidence to answer the question above. 171  HANDS-ON ACTIVITY Disappearing Coins Objective Collaborate to investigate light’s affect on objects. Have you ever Materials pennies tossed coins into a fountain and made a wish? If so, then you have shallow baking pan probably noticed that sometimes you can see the coins in the water masking tape and sometimes you can’t. Is this magic? Not really. It has to do with water how you see light and how it can bend. What question will you investigate to meet this objective? Procedure STEP 1 Place a few pennies into a shallow baking dish. STEP 2 Slowly walk backwards while keeping an eye on the pennies. Stop when you can no longer see them over the side of the pan. Mark your spot on the floor with masking tape. What is the masking tape for? STEP 3 Slowly add water to the pan until © Houghton Mifflin Harcourt it is just about full. Make sure the coins stay in the same place. Why do the coins need to remain in the same spot? 172  STEP 4 Stand on the spot you have marked on the floor. Look at the coins in the pan. Draw what you observe below. Use lines that show how light moves from the coins to your eye. Drain the water from the dish and have your partner repeat this activity. Analyze Your Results STEP 5 How did what you and your partner observe change when the water was added? STEP 6 Stick a pencil straight down into the pan. Look at it from the side of the pan. What do you see? What does this tell you about how light moves? Draw Conclusions STEP 7 What can you claim about light in making the coins visible? © Houghton Mifflin Harcourt STEP 8 Does light always behave in this way? Cite evidence to explain your answer. 173  EXPLORATION 1 Reflection and Our Eyes What Do You See? Imagine you are in a windowless room. There are no lights. Can you see anything? Of course not! Why? You need light to see. Light travels from place to place as a wave. It may come from the sun, a candle, or a flashlight. Once light reaches its target, it might pass through the target. Or it may bounce back. Read these pages to find out more about light. Explore Online Most people close the window blinds in their bedrooms at night to make the room darker. By not letting light into the room, many people can sleep through the night. When window blinds are open, light can enter the room. People need light to see things. With the blinds open, much of the outside light can enter the room. © Houghton Mifflin Harcourt 2. Why can’t you see outside with the blinds closed? 174  This box allows light to This box is translucent, This box prevents any light from pass through it. The box is meaning some light can pass passing through it. The box is transparent, which means through it but is scattered so opaque, which means light light can pass through it. A car no clear image is visible. Waxed cannot pass through it. Most window can be transparent also. paper is also translucent. window blinds are opaque. All, Some, None 3. On the lines, identify each material as opaque, translucent, or transparent. © Houghton Mifflin Harcourt EVIDENCE NOTEBOOK What type of material is a telescope mirror? How does it interact with light? 175 Bouncing Waves Look in the mirror. What do you see? Your reflection looking back at you! A reflection is the bouncing of waves when they hit an obstacle. Anything you can see is either a light source or is reflecting light. In the case of your reflection, the obstacle is the back surface of the mirror. So how does a mirror work? A piece of glass is polished, and then painted with shiny silver paint on one side. When light hits the layer of paint, it is reflected. Many other things can reflect light, too. Common Reflectors 4. View the images and read the captions to learn more about some surfaces that reflect. © Houghton Mifflin Harcourt Image Credits: (tl) ©Keith Brofsky/Getty Images; (tr) ©Getty Mirrors cause light to bounce off them. The A disco ball is made of many tiny mirrors. image in a mirror is backwards because of the When light hits them, it reflects and makes way the light reflects from the mirror. colored spots on the walls. Images; (bl) ©Getty Images; (br) ©George Peters/iStockPhoto.com Some of the sunlight that hits solar panels is Water is a good reflector of light. Sunlight is absorbed and some is reflected. Solar panels bouncing off water in this lake. When the lake is change sunlight into electricity. perfectly still, the water can act like a mirror. 176  Not all reflective surfaces are flat. This sculpture is called Cloud Gate. It is located in Chicago, Illinois. Even though it is not flat, it is very smooth, and light can still bounce off its surface. As you have read, light can be reflected off of different surfaces. And the © Houghton Mifflin Harcourt Image Credits: ©Kjel Larsen/Getty Images surface does not have to be flat to reflect light. The color of an object can also impact how light is reflected. Dark objects usually do not reflect as much light as light-color objects. If you are out after dark, you want to be sure to wear light-color clothing. This way, car headlights will reflect off your clothes and allow drivers to see you. 5. Identify three other things that reflect light. How do you know they are reflecting light waves? 177 Smooth Waves Ahead You’ve learned that many surfaces are smooth and reflective. However, not all smooth things reflect light. There are some surfaces that look smooth to the eyes and even feel smooth to the touch. But when those surfaces are magnified, you can see they are very bumpy. This may impact the surface’s ability to reflect light. Look at the photos on these pages to see how some everyday objects look under a microscope. Even though some objects may appear smooth, their surfaces are really bumpy. The bumps scatter light in different directions making an object less reflective. A piece of paper feels smooth to the touch but is actually very bumpy! The bumps scatter light. © Houghton Mifflin Harcourt Image Credits: (tl) ©Biophoto Associates/Science Source; (inset) ©Fuse/Getty Images; (bl) ©Comstock Images/Getty Images Aluminum is a metal that is used for many things, including foil used in the kitchen. It has a very reflective surface. 178  Hook-and-loop fasteners help objects stick together. They are not reflective. Source; (inset) ©Jan Sandvik/Getty Images; (bl) ©draganajokmanovic/Getty Images; (br) © Houghton Mifflin Harcourt Image Credits: (tl) ©Steve Gschmeissner/Science Gold is a metal often used to make jewelry. The surface of gold is usually reflective. ©Comstock/age fotostock 6. Which three objects will best reflect light? a. a mirror d. a stapler b. a black T-shirt e. a piece of aluminum foil c. a brown piece of paper f. a gold necklace 179 From the Sun to Your Eyes You know that to see something, there has to be light. Your eyes are specially adapted to collect as much light as possible. Imagine you’re outside on a sunny day, playing catch with a friend. You can see your friend standing a few meters away. You can see the object she’s tossing to you. All of this is possible because light is bouncing off everything and entering your eyes. In order to see an object, it must be emitting light, like the sun, or light needs to bounce off it. What happens on a sunny day? Light from the sun reaches Earth. The light reflects off an object. Then, the light hits the surface of the eye. 7. What would happen to the path of light if it hit a transparent surface like a glass window? a. The light would change direction. b. The light would reflect off it. c. The light would pass through it. d. The light would scatter all around. HANDS-ON Apply What You Know © Houghton Mifflin Harcourt Seeing Color 8. How do colored filters change the way we see? Using transparent colored light filters, observe the clothing of your classmates. What does a red shirt look like through a red filter? Does a green shirt appear the same through the same red filter? Make a chart to describe what different colors look like through the filters. What patterns do you see in your data? 180  Let’s Make Colors! Light is made up of many different colors all blended together. Each color of the rainbow has a different wavelength. As a result, you see a red apple as red because the red wavelengths are being reflected by the apple’s skin. The other wavelengths are absorbed by the apple. These four objects are reflecting and absorbing light differently. The bowling ball is absorbing all wavelengths of visible light. The blue balloon is reflecting blue wavelengths but absorbing all the others. The volleyball is reflecting all wavelengths. The orange is reflecting orange wavelengths but absorbing other wavelengths of light. © Houghton Mifflin Harcourt Image Credits: C Squared Studios/PhotoDisc/Getty Images 9. Look at the object to the right. Explain how it is absorbing and reflecting visible light. Putting It Together 10. Select the words to correctly complete each sentence. white black opaque transparent Light reflects from surfaces and passes through ones. objects reflect all wavelengths of light. objects absorb all visible light. 181  HANDS-ON ACTIVITY Reflecting on Angles Consider This Have you ever been to a carnival that had a fun house? Sometimes these places have fun mirrors. When you look Materials 10 cm × 10 cm into them, your reflection can be squashed, stretched out, or even piece of cardboard pencil thin. How do these mirrors work? Well it all has to do with small mirror the reflection of light. These mirrors are bent in a certain way. This modeling clay bending changes the angle at which light hits them to make the 3 pushpins of funny images you see. different colors labels metric ruler Objective protractor Collaborate to investigate how angles of reflection affect light. What question will you answer during your investigation? Procedure STEP 1 Stand the mirror up at the end of the cardboard using the clay. STEP 2 Label the pushpins PP1, PP2, and PP3. Place PP1 and PP2 into the cardboard 5 cm from the mirror. Why does the position of the pushpins matter? © Houghton Mifflin Harcourt STEP 3 Position yourself so that PP1 lines up with the reflection of PP2. 182  STEP 4 Put PP3 into the cardboard at the end of the mirror in front of PP2’s reflection. PP1, PP3, and the reflection of PP2 should make a straight line. STEP 5 Draw lines on the cardboard to connect PP3 with PP1 and PP2. STEP 6 Draw lines along the front of the mirror and then remove it. STEP 7 Use a protractor to measure the angles between each of the PP lines and the mirror line. Why did you remove the mirror during this step of the investigation? STEP 8 Draw a picture of your cardboard as seen from above. Include the point each pin forms as well as the angle formed by the pins. © Houghton Mifflin Harcourt 183 Analyze Your Results STEP 9 What shape did the lines make when you recorded their angles? Why? STEP 10 Why was it important to start this activity with PP1 and the reflection of PP2 in the same line? Draw Conclusions STEP 11 Use evidence from this activity to make a claim about how light travels and behaves when it strikes an object. STEP 12 What effect would moving one of the pushpins farther from the mirror have on the angle? © Houghton Mifflin Harcourt STEP 13 What are some other questions you have about how light reflects from a surface? 184  EXPLORATION 2 Refraction and Lenses Seeing Light Light moves faster than any other wave or object, but its speed can change. Light moves much faster in air than it does in the water. When light hits a liquid like water it bends. The sun is millions of kilometers away from White light is made of different colors of light. Earth. Thus, it takes time for its light to reach So when white light shines through a prism or us. The sunlight you see at any time left the sun passes through raindrops, it is separated into the © Houghton Mifflin Harcourt Image Credits: (l) ©djgis/Shutterstock; (r) ©GIPhotoStock/ eight minutes before you see it! colors of the rainbow. Do the Math Convert Units of Time 11. The sun is millions of kilometers from Earth. When light leaves the sun, it takes eight minutes to reach Earth. It takes sunlight 12 minutes and 40 seconds to reach Mars. How much longer, in seconds does it take sunlight to reach Mars? Science Source 185 Breaking Straws Think back to the Disappearing Coins activity. The coins were not visible from a distance when the pan had no water. Once water was added, the coins were visible. This was an optical illusion caused by refraction. Refraction is the bending of light waves as they pass from one material to another. Light changes direction and speed when it hits a barrier. Look at the photos to see how refraction can affect how things appear. 12. Why does the straw in the photo appear to be bent? © Houghton Mifflin Harcourt Image Credits: (br) ©A & J Visage/Alamy An archerfish is able to see insects on plants that are above the water. When the fish hunts for food, it watches an insect to set up its attack. To capture its prey, the fish squirts water out of its mouth, at just the right angle to account for refraction. The water hits the insect and knocks it into the water. 186  To better understand refraction, think about the following. A group of students is walking in a straight line and at a fast pace. When the students reach a line drawn on the ground, they slow down, which also causes them to change direction. Every time a student crosses the line, he or she does this. These students represent light waves. The line on the ground is the boundary between any two materials. The shift is the refraction caused when the waves change direction and speed. Language SmArts Using Word Parts 13. Use a dictionary to divide the words reflection and refraction into parts. Write original definitions for each word using the definitions of its parts. © Houghton Mifflin Harcourt 14. Chose the words to correctly complete each sentence. broken medium refraction is the bending of a light wave. This happens when the wave changes. This interaction can make objects appear. 187 Lenses Some objects, such as cells, are too small to see with the unaided eye. Other objects, such as stars, are too far away. Over time, many tools have been invented to help people look at objects they otherwise would not be able to see. Many of these tools contain lenses. A lens is a piece of plastic or glass that magnifies an object. Some lenses are curved; others are flat. Read on to find out more about how lenses have helped us. Smile! 15. As you read about this camera, underline key phrases to help you remember how a camera such as this one works. Have you ever used a camera? If so, you may know that it has several important parts. Cameras need light to take pictures. This light gets manipulated by the lenses in the camera. After the light comes through the lenses, it bounces off a mirror, reflects two more times inside a prism, and then forms an image in the eye piece. The lens of this camera is a collection of curved pieces of glass that magnify an image. Larger lenses are able to refract more light than smaller lenses. The mirror in this camera reflects the light that enters through the lenses and moves it toward the viewfinder. The mirror flips up just before a © Houghton Mifflin Harcourt picture is taken. EVIDENCE NOTEBOOK How do lenses and mirrors affect light? 188  Imagine you are out at sea on a boat. You see something in the distance but can’t make out what it is. You take out your binoculars to get a better look. Binoculars are useful for seeing things that are far away. They use a series of lenses to collect and bend light to magnify an object. They work a lot like telescopes but are not as powerful. Now imagine being at the park. You find a small pebble that has a bunch of shiny flecks in it. You want to get a better look at them, so you pull out your hand lens. Hand lenses are sometimes called magnifying glasses. They’re great tools to use to see small things. They have curved lenses that change how the light goes through them to make things look bigger. © Houghton Mifflin Harcourt Image Credits: (t) Comstock; (c) ©mustafa deliormanli/ You know that there are many creatures on Earth too small to see with an unaided eye. But did you know that there are parts of these creatures that are really, really small? To see these small creatures iStockPhoto.com; (b) ©mmpile/Getty Images and their parts, you could use a microscope. Like binoculars and hand lenses, microscopes use lenses to make objects look larger than they really are. 16. Which of the following refract light to produce images of objects? Select all that apply. a. binoculars d. car windshields b. hand lenses e. microscopes c. windows in a house f. mirrors 189 Human Lenses You know that to see something, there needs to be light. Your eyes have special parts that collect visible light so that you can see the world around you. Just like a camera or a telescope, each of your eyes has a lens. The job of the lens is to focus the light. Remember that light travels in a straight line to your eyes. Once the light enters your eyes, it goes through different parts of your eyes and brain before you see an image. Because light moves so fast, this process happens nearly instantly. From the Sun to You Explore 17. Use the information above, the drawing, and the information Online below to answer the question. Light leaves the sun and then reflects off of an object. The reflected light hits the surface of the eye and travels through the lens to a focal point inside the eye. There the light is changed into signals and sent to the brain. The brain figures out the signals, and you understand what you see. © Houghton Mifflin Harcourt What happens at the focal point inside the eye? 190  18. Write or diagram the process that produces vision into a flow chart showing six steps. a. b. c. d. e. f. 19. Choose the words to correctly complete each sentence. air brain eyes light spine reflects refracts In order to see, must be present. Light off of objects and enters the. © Houghton Mifflin Harcourt There it is changed into a signal that is passed to the. The signals are used to produce an image. This is how you see things. EVIDENCE NOTEBOOK How does the lens in your eye work to produce an image? 191 Super Lenses You probably know a few people who wear glasses to help them see. Eyeglasses are lenses used to correct vision problems. The two main types of lenses used in glasses are convex lenses and concave lenses. Both lenses allow light to pass into them, but each interacts with light in different ways. Study the drawings to see how these lenses compare. JVU]L_SLUZ YH`ZVMSPNO[ JVUJH]LSLUZ YH`ZVMSPNO[ © Houghton Mifflin Harcourt Image Credits: (r) ©wavebreakmedia/Getty Images Convex lenses are curved outwards. Concave Eyeglasses are often used to correct vision lenses are curved inwards. Notice how these problems. Some people do not have to wear differences cause light to behave once it enters glasses until they are older. Others start when the lenses. they are young. 20. Use the information and drawings to complete the table below to compare and contrast convex and concave lenses. Convex Both Concave 192  HANDS-ON Apply What You Know Read This! 21. Get a convex and a concave lens from your teacher. Use each lens to look at different types of printed materials. Place one lens over the words on a worksheet or this book page. Note whether the words appear larger or smaller. Then use the other lens and do the same thing. How does the print look different with the different lenses? Telescopes can be used to see things that are millions and millions of kilometers from Earth. Telescopes may use lenses, mirrors, or a combination of both to gather and bend light. A refracting telescope has a curved primary lens that gathers light and bends it. It then sends the light waves to another lens called the eyepiece. This is the part through which you look. A refracting telescope bends light to produce a magnified image of a distant object. © Houghton Mifflin Harcourt Image Credits: ©Don Smetzer/Alamy 22. Choose the word or phrase to correctly complete each sentence. bend bounce off concave convex far away close up lenses focus light into a single point. lenses cause light to spread out. Refracting telescopes cause light to and are used to view objects that are. 193  Engineer It! Designed for Safety Have you ever noticed words printed on the passenger-side mirror of a car? The message says: Objects in mirror are closer than they appear. What does this message mean? These side mirrors might appear flat, but if you examine them very closely, you can see that they have a curved surface. They are slightly convex. The driver in a car is sitting several feet away from the passenger-side mirror. The mirror is in a fixed position so that it reflects just a section of what is on that side of the car for the driver to see. A convex mirror reflects more of the view on that side of the car than a flat mirror surface would. But the tradeoff for seeing more is that the driver doesn’t perceive the distance to the objects in the mirror accurately. Why does this matter? One of the things a driver uses mirrors for is backing up a vehicle. If a driver is backing a car toward an object in the mirror, it is important to know that the object is closer than his or her eyes might think! © Houghton Mifflin Harcourt Image Credits: (tr) ©Patrick Strattner/fStop/Getty Images 23. If a convex car mirror makes objects appear closer than they really are, what do you think the reflection in a concave mirror would look like? Language SmArts Tip Identifying Main Ideas and Details The English 24. Identify the main idea of the passage on this page. Then write Language Arts down at least three details that support this idea. Handbook can provide help with understanding how to identify the main idea. 194  TAKE IT FURTHER Discover More Check out this path... or go online to choose one of these other paths. People in Light and Art Science & Lighthouses and Lenses Engineering People in Science & Engineering: Optics Engineers Microscopes, telescopes, and lasers are all tools that make use of light, mirrors, and lenses. Without knowing how light behaves, none of these would have been invented. People who design tools that use light are called optical engineers. They investigate how light refracts and reflects. They use this knowledge to invent tools that can be used in many different fields. For example, lasers are beams of light that can be used to carry out a delicate surgery. Lasers are also used to scan products at the checkout counter or produce a light show at a rock concert. Optical engineers, like Dr. Kristopher Davis, use knowledge of light and lenses to help © Houghton Mifflin Harcourt engineers design useful tools, such as video projectors, laser printers, or even the Hubble Space Telescope. Optical engineers at the University of Central Florida developed technology to test the efficiency, or the ability to produce electrical energy with less waste, of solar cells like this. 195  Like with most fields of research today, optical engineers commonly use computers to design models. They also use computers to test their models. In this field, it is important to have a very strong background in both math and science. A few of the latest discoveries coming out of this engineering field include a communications cable that can carry 22 times more signal than regular cables. Another discovery is flexible glass that can be used in the fields of communications and energy exploration. These discoveries, along with many, many others, will lead the way as the technology and optics age continues. Dr. Davis and the UCF optics team use LEDs with different wavelengths of light attached to a system of fiber optic cables to test solar cell efficiency. By understanding how efficient a solar cell is, optical engineers can alter and improve their design, so they produce more electrical energy. Optical engineers at UCF also conduct research on lasers like this one, fiber optics, and optical imagery for medical fields. The goal of each research field is to improve our every day lives with optical materials that are stronger, faster, and more efficient. © Houghton Mifflin Harcourt 25. Research other aspects of optical engineering. What kind of training does someone need to become an optical engineer? Would you enjoy working in this field? Why? 196  LESSON 2 Lesson Check Name Can You Explain It? Explore 1. Now that you know about lenses and Online how they interact with light, explain how a telescope allows us to see things millions of kilometers away. Be sure to do the following: Describe how light moves. Explain how light reflects and refracts. Detail how light allows you to see objects. EVIDENCE NOTEBOOK Use the information you’ve gathered in your Evidence Notebook to help you cover each point above. © Houghton Mifflin Harcourt Image Credits: ©Science Source Checkpoints 2. You shine a light into a dark container. The light shines back at you. Which of these terms describe the container and behavior of the light? Select all that apply. a. reflection b. refraction c. opaque d. transparent e. translucent 197 3. Choose the word or phrase that correctly completes each sentence. bend destroy stay in place move angles heights eye brain Water can light. Coins thrown into a fountain look like they when looked at from different. This is because the water creates an illusion. Your is tricked into thinking the coins have moved. 4. You put a spoon into a clear glass of water. When you look at the spoon, it appears bent. Which of these describes the glass of water and the behavior of the light? Select all that apply. a. reflection d. transparent b. refraction e. translucent c. opaque 5. You shine a flashlight into a glass of apple juice. Some of the light bounces off the liquid. Some of it passes through it. Which of these describe the juice and the light behavior? Select all that apply. a. reflection d. transparent b. refraction e. translucent c. opaque 6. Label each object as opaque, transparent, or translucent. © Houghton Mifflin Harcourt 198  LESSON 2 Lesson Roundup A. You throw a penny into a fountain. You see where it lands. Your little brother cannot. He is standing next to you. Which of these explains why this is so? Select all that apply. a. Light was reflected. d. The water is opaque. b. Light was refracted. e. The water is too cold. c. He’s at the wrong angle. f. The penny is reflecting light. B. Order the steps to show how light from the sun allows you to see an object. You see the object. Light is changed into a signal. Light leaves the sun. Signal enters the brain. Light reflects off of an object. Light enters the lens in your eye. C. Choose the word or words that correctly describe each object and how © Houghton Mifflin Harcourt Image Credits: (tl) ©C Squared Studios/PhotoDisc/Getty light behaves in the situation. reflection refraction passes through opaque transparent translucent Images; (br) ©Stockdisk/Getty Images D. Which of these describes a lens that causes light to spread out when it focuses it? a. translucent c. concave b. opaque d. convex 199