Light Mirrors and Lenses (3379.0K) - McGraw-Hill Higher Education

Start-Up ActivitiesBending LightEverything you see results from light wavesentering your eyes. These light waves areeither given off by objects, such as the Sunand lightbulbs, or reflected by objects, suchas trees, books, and people. Lenses and mirrorscan cause light to change direction andmake objects seem larger or smaller.Light, Mirrors, and LensesMake the following Foldable tohelp you understand the propertiesof and the relationship between light, mirrors,and lenses.STEP 1Fold a sheet of pape in half lengthwise.Make the back edge about 5 cmlonger than the front edge.1. Place two paper cups next to each otherand put a penny in the bottom of each cup.2. Fill one of the cups with water andobserve how the penny looks.3. Looking straight down at the cups, slidethe cup with no water away from you justuntil you can no longer see the penny.4. Pour water into this cup and observe whatseems to happen to the penny.5. Think Critically In your ScienceJournal, record your observations. Didadding water make the cup look deeperor shallower?STEP 2STEP 3STEP 4Turn the paper so thefold is on the bottom.Then fold it intothirds.Unfold and cut only the top layeralong folds to make three tabs.Label the Foldable as shown.Light, Mirrors, and LensesLight Mirrors LensesPreview this chapter’s contentand activities atips.msscience.comSummarize in a Table As you read the chapter,summarize the information you find about light,mirrors, lenses.549Chad Ehlers/Index Stock

Properties of Light■ Describe the wave nature oflight.■ Explain how light interacts withmaterials.■ Determine why objects appearto have color.Everything you see comes frominformation carried by light waves.Review Vocabularyelectromagnetic waves: wavescreated by vibrating electriccharges that can travel throughspace or through matterNew Vocabularylight ray• mediumWhat is light?Drop a rock on the smooth surface of a pond and you’ll seeripples spread outward from the spot where the rock struck. Therock produced a wave much like the one in Figure 1. A wave isa disturbance that carries energy through matter or space. Thematter in this case is the water, and the energy originally comesfrom the impact of the rock. As the ripples spread out, they carrysome of that energy.Light is another type of wave that carries energy. A source oflight such as the Sun or a lightbulb gives off light waves intospace, just as the rock hitting the pond causes waves to form inthe water. But while the water waves spread out only on the surfaceof the pond, light waves spread out in all directions fromthe light source. Figure 1 shows how light waves travel.Sometimes, however, it is easier to think of light in a differentway. A light ray is a narrow beam of light that travels in astraight line. You can think of a source of light as giving off, oremitting, a countless number of light rays that are travelingaway from the source in all directions.Figure 1 Light movesaway in all directionsfrom a light source,just as ripples spreadout on the surfaceof water.A source of light, such as a lightbulb,gives off light rays that travel awayfrom the light source in all directions.Ripples on the surface of a pond are produced by anobject hitting the water. The ripples spread outfrom the point of impact.550 CHAPTER 19 Light, Mirrors, and LensesDick Thomas/Visuals Unlimited

Light Travels Through Space There is, however, oneimportant difference between light waves and the water waveripples on a pond. If the pond dried up and had no water, ripplescould not form. Waves on a pond need a material—water—in which to travel. The material through which a wave travels iscalled a medium. Light is an electromagnetic wave and doesn’tneed a medium in which to travel. Electromagnetic waves cantravel in a vacuum, as well as through materials such as air,water, and glass.Light and MatterWhat can you see when you are in a closed room with nowindows and the lights out? You can see nothing until you turnon a light or open a door to let in light from outside the room.Most objects around you do not give off light on their own.They can be seen only if light waves from another source bounceoff them and into your eyes, as shown in Figure 2. The processof light striking an object and bouncing off is called reflection.Right now, you can see these words because light emitted by asource of light is reflecting from the page and into your eyes.Not all the light rays reflected from the page strike your eyes.Light rays striking the page are reflected in many directions, andonly some of these rays enter your eyes.What must happen for you to see most objects?Observing Colorsin the DarkProcedure1. Get six pieces of paperthat are different colorsand about 10 cm 10 cm.2. Darken a room and wait10 min for your eyes toadjust to the darkness.3. Write on each paper whatcolor you think the paper is.4. Turn on the lights and seeif your night vision correctlydetected the colors.Analysis1. If the room were perfectlydark, what would you see?Explain.2. Your eyes contain rod cellsand cone cells. Rod cellsenable you to see in dimlight, but don’t detectcolor. Cone cells enableyou to see color, but do notwork in dim light. Whichtype of cell was working inthe darkened room?Explain.Figure 2 Light waves are givenoff by the lightbulb. Some of theselight waves hit the page and arereflected. The student sees the pagewhen some of these reflected wavesenter the student’s eyes.SECTION 1 Properties of Light 551John Evans

A pair of gym shoes and socks as seenunder white light.The same shoes and socks photographedthrough a red filter.Why do objects have color? Why does grass look green ora rose look red? When a mixture of light waves strikes an objectthat is not transparent, the object absorbs some of the lightwaves. Some of the light waves that are not absorbed arereflected. If an object reflects red waves and absorbs all the otherwaves, it looks red. Similarly, if an object looks blue, it reflectsonly blue light waves and absorbs all the others. An object thatreflects all the light waves that strike it looks white, while onethat reflects none of the light waves that strike it looks black.Figure 5 shows gym shoes and socks as seen under white lightand as seen when viewed through a red filter that allows only redlight to pass through it.Primary Light Colors How many colors exist? People oftensay white light is made up of red, orange, yellow, green, blue, andviolet light. This isn’t completely true, though. Many more colorsthan this exist. In reality, most humans can distinguish thousandsof colors, including some such as brown, pink, and purple,that are not found among the colors of the rainbow.Light of almost any color can be made by mixingdifferent amounts of red, green, and blue light. Red,green, and blue are known as the primary colors.Look at Figure 6. White light is produced wherebeams of red, green, and blue light overlap. Yellowlight is produced where red and green light overlap.You see the color yellow because of the way yourbrain interprets the combination of the red andgreen light striking your eye. This combination oflight waves looks the same as yellow light producedby a prism, even though these light waves have onlya single wavelength.Figure 5 The color of an objectdepends on the light waves itreflects.Infer why the blue socks look blackwhen viewed under red light.Figure 6 By mixing light fromthe three primary colors—red,blue, and green—almost all of thevisible colors can be made.SECTION 1 Properties of Light 553Mark Thayer

Figure 7 The three primarycolor pigments—yellow,magenta, and cyan—can formalmost all the visible colors whenmixed together in variousamounts.Primary Pigment Colors Materials like paint that are usedto change the color of other objects, such as the walls of a roomor an artist’s canvas, are called pigments. Mixing pigmentstogether forms colors in a different way than mixing coloredlights does.Like all materials that appear to be colored, pigments absorbsome light waves and reflect others. The color of the pigmentyou see is the color of the light waves that are reflected from it.However, the primary pigment colors are not red, blue, andgreen—they are yellow, magenta, and cyan. You can makealmost any color by mixing different amounts of these primarypigment colors, as shown in Figure 7.Although primary pigment colors are not the same as theprimary light colors, they are related. Each primary pigmentcolor results when a pigment absorbs a primary light color. Forexample, a yellow pigment absorbs blue light and it reflects redand green light, which you see as yellow. A magenta pigment, onthe other hand, absorbs green light and reflects red and bluelight, which you see as magenta. Each of the primary pigmentcolors is the same color as white light with one primary colorremoved.SummaryLight•and MatterLight is an electromagnetic wave that can•travel in a vacuum as well as through matter.When light waves strike an object some lightwaves might be absorbed by the object, somewaves might be reflected from the object, and•some waves might pass through the object.Materials can be opaque, translucent, ortransparent, depending on how much lightpasses through the material.•ColorLight waves with different wavelengths have•different colors.White light is a combination of all the colors•ranging from red to violet.The color of an object is the color of the light•waves that it reflects.The primary light colors are red, green, andblue. The primary pigment colors are yellow,magenta and cyan.Self Check1. Diagram the path followed by a light ray that entersone of your eyes when you are reading at night in aroom.2. Determine the colors that are reflected from an objectthat appears black.3. Compare and contrast primary light colors and primarypigment colors.4. Describe the difference between an opaque object anda transparent object.5. Think Critically A white shirt is viewed through a filterthat allows only blue light to pass through the filter.What color will the shirt appear to be?6. Draw Conclusions A black plastic bowl and a whiteplastic bowl are placed in sunlight. After 15 minutes,the temperature of the black bowl is higher than thetemperature of the white bowl. Which bowl absorbsmore light waves and which bowl reflects more lightwaves?554 CHAPTER 19 Light, Mirrors, and Lensesips.msscience.com/self_check_quiz

Reflection and MirrorsThe Law of ReflectionYou’ve probably noticed your image on the surface of a poolor lake. If the surface of the water was smooth, you could seeyour face clearly. If the surface of the water was wavy, however,your face might have seemed distorted. The image you saw wasthe result of light reflecting from the surface and traveling toyour eyes. How the light was reflected determined the sharpnessof the image you saw.When a light ray strikes a surface and is reflected, as inFigure 8, the reflected ray obeys the law of reflection. Imaginea line that is drawn perpendicular to the surface where thelight ray strikes. This line is called the normal to the surface.The incoming ray and the normal form an angle called theangle of incidence. The reflected light ray forms an angle withthe normal called the angle of reflection. According to thelaw of reflection, the angle of incidence is equal to the angle ofreflection. This is true for any surface, no matter what materialit is made of.Reflection from SurfacesWhy can you see your reflection in some surfaces and notothers? Why does a piece of shiny metal make a good mirror, buta piece of paper does not? The answers have to do with thesmoothness of each surface.■ Explain how light is reflectedfrom rough and smooth surfaces.■ Determine how mirrors form animage.■ Describe how concave and convexmirrors form an image.Mirrors can change the direction oflight waves and enable you to seeimages, such as your own face.Review Vocabularynormal: a line drawn perpendicularto a surface or lineNew Vocabularylaw of reflection•focal pointfocal lengthAngle ofreflectionReflected rayMirrorFigure 8 A light ray strikes asurface and is reflected. The angleof incidence is always equal to theangle of reflection. This is the lawof reflection.NormalAngle ofincidenceIncident raySECTION 2 Reflection and Mirrors 555

Figure 9 A highly magnifiedview of the surface of a sheet ofpaper shows that the paper ismade of many cellulose woodfibers that make the surfacerough and uneven.Magnification: 80Regular and Diffuse Reflection Eventhough the surface of the paper might seemsmooth, it’s not as smooth as the surface of amirror. Figure 9 shows how rough the surfaceof a piece of paper looks when it is viewedunder a microscope. The rough surface causeslight rays to be reflected from it in many directions,as shown in Figure 10. This unevenreflection of light waves from a rough surfaceis diffuse reflection. The smoother surfaces ofmirrors, as shown in Figure 10, reflect lightwaves in a much more regular way. For example, parallel raysremain parallel after they are reflected from a mirror. Reflectionfrom mirrors is known as regular reflection. Light waves that areregularly reflected from a surface form the image you see in amirror or any other smooth surface. Whether a surface issmooth or rough, every light ray that strikes it obeys the law ofreflection.Why does a rough surface cause a diffusereflection?Scattering of Light When diffuse reflection occurs, lightwaves that were traveling in a single direction are reflected andthen travel in many different directions. Scattering occurs whenlight waves traveling in one direction are made to travel in manydifferent directions. Scattering also can occur when light wavesstrike small particles, such as dust. You may have seen dust particlesfloating in a beam of sunlight. When the light waves in thesunbeam strike a dust particle, they are scattered in all directions.You see the dust particles as bright specks of light whensome of these scattered light waves enter your eye.Figure 10 The roughness of asurface determines whether itlooks like a mirror.AA rough surface causes parallellight rays to be reflected inmany different directions.BA smooth surface causes parallellight rays to be reflected in asingle direction. This type ofsurface looks like a mirror.556 CHAPTER 19 Light, Mirrors, and Lenses(l)Susumu Nishinaga/Science Photo Library/Photo Researchers, (r)Matt Meadows

ImageWallMirrorLight rays that bounce off a person strike the mirror.Some these light rays are reflected into the person’s eye.MirrorWallThe light rays that are shown entering the person’seye seem to be coming from a person behind the mirror.Reflection by Plane Mirrors Did you glance in the mirrorbefore leaving for school this morning? If you did, you probablylooked at your reflection in a plane mirror. A plane mirror is amirror with a flat reflecting surface. In a plane mirror, yourimage looks much the same as it would in a photograph.However, you and your image are facing in opposite directions.This causes your left side and your right side to switch places onyour mirror image. Also, your image seems to be coming frombehind the mirror. How does a plane mirror form an image?Figure 11 A plane mirror formsan image by changing the directionof light rays.Describe how you and your imagein a plane mirror are different.What is a plane mirror?Figure 11 shows a person looking into a plane mirror. Lightwaves from the Sun or another source of light strike each part ofthe person. These light rays bounce off the person according tothe law of reflection, and some of them strike the mirror. Therays that strike the mirror also are reflected according to the lawof reflection. Figure 11A shows the path traveled by a few of therays that have been reflected off the person and reflected back tothe person’s eye by the mirror.The Image in a Plane Mirror Why does the image you seein a plane mirror seem to be behind the mirror? This is a resultof how your brain processes the light rays that enter your eyes.Although the light rays bounced off the mirror’s surface, yourbrain interprets them as having followed the path shown by thedashed lines in Figure 11B. In other words, your brain alwaysassumes that light rays travel in straight lines without changingdirection. This makes the reflected light rays look as if they arecoming from behind the mirror, even though no source of lightis there. The image also seems to be the same distance behindthe mirror as the person is in front of the mirror.Light Waves and PhotonsWhen an object like a marbleor a basketball bouncesoff a surface, it obeys thelaw of reflection. Becauselight also obeys the law ofreflection, people oncethought that light must be astream of particles. Today,experiments have shownthat light can behave asthough it were both a waveand a stream of energy bundlescalled photons. Readan article about photonsand write a description inyour Science Journal.SECTION 2 Reflection and Mirrors 557

Topic: Concave MirrorsVisit ips.msscience.com for Weblinks to information about theconcave mirrors used in telescopes.Activity Make a chart showingthe five largest telescope mirrorsand where they are located.Concave and Convex MirrorsSome mirrors are not flat. A concave mirror has a surfacethat is curved inward, like the bowl of a spoon. Unlike planemirrors, concave mirrors cause light rays to come together, orconverge. A convex mirror, on the other hand, has a surface thatcurves outward, like the back of a spoon. Convex mirrors causelight waves to spread out, or diverge. These two types of mirrorsform images that are different from the images that are formedby plane mirrors. Examples of a concave and a convex mirrorare shown in Figure 12.What’s the difference between a concave andconvex mirror?Figure 12 Convex and concavemirrors have curved surfaces.Concave Mirrors The way in which a concave mirror formsan image is shown in Figure 13. A straight line drawn perpendicularto the center of a concave or convex mirror is called theoptical axis. Light rays that travel parallel to the optical axis andstrike the mirror are reflected so that they pass through a singlepoint on the optical axis called the focal point. The distancealong the optical axis from the center of the mirror to the focalpoint is called the focal length.The image formed by a concave mirror depends on the positionof the object relative to its focal point. If the object is fartherfrom the mirror than the focal point, the image appears tobe upside down, or inverted. The size of the image decreases asthe object is moved farther away from the mirror. If the object iscloser to the mirror than one focal length, the image is uprightand gets smaller as the object moves closer to the mirror.A concave mirror can produce a focused beam of light if asource of light is placed at the mirror’s focal point, as shown inFigure 13. Flashlights and automobile headlights use concavemirrors to produce directed beams of light.A concave mirrorhas a surface that’scurved inward.A convex mirror hasa surface that’scurved outward.558 CHAPTER 19 Light, Mirrors, and Lenses(l)Matt Meadows, (r)Paul Silverman/Fundamental Photographs

VISUALIZING REFLECTIONS IN CONCAVEMIRRORSFigure 13Glance into a flat plane mirror andyou’ll see an upright image of yourself.But look into a concave mirror,and you might see yourself larger than life,right side up, or upside down—or not atall! This is because the way a concave mirrorforms an image depends on the positionof an object in front of the mirror, asshown here.Optical axisFocalpointA concave mirror reflects all light rays travelingparallel to the optical axis so that they pass throughthe focal point.ObjectFocalpointFocal pointOptical axisOptical axisInverted imageWhen an object, such as this flower, isplaced beyond the focal point, the mirrorforms an image that is inverted.When a source of light is placed at the focal point,a beam of parallel light rays is formed. The concavemirror in a flashlight, for example, creates a beam ofparallel light rays.ObjectUpright imageFocal pointOptical axisIf the flower is between the focalpoint and the mirror, the mirrorforms an upright, enlarged image.SECTION 2 Reflection and Mirrors 559(l)Digital Stock, (r)Joseph Palmieri/Pictor

Figure 14 A convex mirror is a mirror that curves outward.Optical axisStudentConvex mirrorsurfaceImageA convex mirror causes light rays thatare traveling parallel to the opticalaxis to spread apart after they arereflected.Optical axisNo matter how far an object isfrom a convex mirror, the imageis always upright and smallerthan the object.Convex Mirrors A convexmirror has a reflecting surfacethat curves outward and causeslight rays to spread apart, ordiverge, as shown in Figure 14.Like the image formed by planemirror, the image formed by aconvex mirror seems to bebehind the mirror. Figure 14shows that the image always isupright and smaller than theobject.Convex mirrors often areused as security mirrors instores and as outside rearviewmirrors on cars and othervehicles. You can see a largerarea reflected in a convex mirrorthan in other mirrors.SummaryReflection•and Plane MirrorsThe law of reflection states that the angle of•incidence equals the angle of reflection.A regular reflection is produced by a smoothsurface, such as a mirror. A rough surface•forms a diffuse reflection.Scattering occurs when light rays traveling inone direction are made to travel in many•directions.A plane mirror forms a image that is reversedleft to right and seems to be behind the mirror.•Concave and Convex MirrorsConcave mirrors curve inward and make light•rays converge.Images formed by a concave mirror can beeither upright or inverted and can vary from•larger to smaller than the object.Convex mirrors curve outward and make light•rays diverge.Images formed by a convex mirror are alwaysupright and smaller than the object.Self Check1. Describe the image formed by a concave mirrorwhen an object is less than one focal length fromthe mirror.2. Explain why concave mirrors are used in flashlights andautomobile headlights.3. Describe If an object is more than one focal lengthfrom a concave mirror, how does the image formed bythe mirror change as the object moves farther from themirror?4. Determine which light rays striking a concave mirrorare reflected so that they pass through the focal point.5. Think Critically After you wash and wax a car, youcan see your reflection in the car’s surface. Before youwashed and waxed the car, no reflection could be seen.Explain.6. Use a Spreadsheet Make a table using a spreadsheetcomparing the images formed by plane, concave, andconvex mirrors. Include in your table how the imagesdepend on the distance of the object from the mirror.560 CHAPTER 19 Light, Mirrors, and Lensesips.msscience.com/self_check_quiz

A light ray strikes the surface of a plane mirrorand is reflected. Does a relationship existbetween the direction of the incoming light rayand the direction of the reflected light ray?Reflection froma Plane MirrorReal-World QuestionHow does the angle of incidence compare withthe angle of reflection for a plane mirror?Goals■ Measure the angle of incidence and theangle of reflection for a light ray reflectedfrom a plane mirror.Materialsflashlightprotractormetric rulerscissorstapeSafety Precautionssmall plane mirror,at least 10 cm on a sideblack construction papermodeling claywhite unlined paperProcedure1. With the scissors, cut a slit in the constructionpaper and tape it over the flashlight lens.2. Place the mirror at one end of the unlinedpaper. Push the mirror into lumps of clay soit stands vertically, and tilt the mirror so itleans slightly toward the table.3. Measure with the ruler to find the centerof the bottom edge of the mirror, andmark it. Then use the protractor and theruler to draw a line on the paper perpendicularto the mirror from the mark. Labelthis line P.4. Draw lines on the paper from the centermark at angles of 30°, 45°, and 60° to line P.5. Turn on the flashlight and place it so thebeam is along the 60° line. This is the angleof incidence. Measure and record the anglethat the reflected beam makes with line P.This is the angle of reflection. If you cannotsee the reflected beam, slightly increase thetilt of the mirror.6. Repeat step 5 for the 30°, 45°, and P lines.Conclude and ApplyInfer from your results the relationshipbetween the angle of incidence and the angleof reflection.Make a poster that shows your measuredangles of reflection for angles of incidenceof 30°, 45°, and 60°. Write the relationshipbetween the angles of incidence andreflection at the bottom.LAB 561Geoff Butler

Refraction and Lenses■ Determine why light raysrefract.■ Explain how convex and concavelenses form images.Many of the images you see everyday in photographs, on TV, and inmovies are made using lenses.Review Vocabularyrefraction: bending of a wave asit changes speed, moving fromone medium to anotherNew Vocabularylens•convex lensconcave lensBending of Light RaysObjects that are in water can sometimes look strange. A pencilin a glass of water sometimes looks as if it’s bent, or as if thepart of the pencil in air is shifted compared to the part in water.A penny that can’t be seen at the bottom of a cup suddenlyappears as you add water to the cup. Illusions such as these aredue to the bending of light rays as they pass from one materialto another. What causes light rays to change direction?The Speeds of Light The speed of light in empty space isabout 300 million m/s. Light passing through a material such asair, water, or glass, however, travels more slowly than this. Thisis because the atoms that make up the material interact with thelight waves and slow them down. Figure 15 compares the speedof light in some different materials.AirThe speed of light through air is about 300 million m/s.WaterFigure 15 Light travels atdifferent speeds in differentmaterials.The speed of light through water is about 227 million m/s.GlassThe speed of light through glass is about 197 million m/s.DiamondThe speed of light through diamond is about 125 million m/s.562 CHAPTER 19 Light, Mirrors, and Lenses

The Refraction of Light WavesLight rays from the part of a pencil that is underwatertravel through water, glass, and then air beforethey reach your eye. The speed of light is different ineach of these mediums. What happens when a lightwave travels from one medium into another in whichits speed is different? If the wave is traveling at anangle to the boundary between the two media, itchanges direction, or bends. This bending is due tothe change in speed the light wave undergoes as itmoves from one medium into the other. The bendingof light waves due to a change in speed is calledrefraction. Figure 16 shows an example of refraction.The greater the change in speed is, the more the lightwave bends, or refracts.What causes light to bend?Why does a change in speed cause the light wave to bend?Think about what happens to the wheels of a car as they movefrom pavement to mud at an angle, as in Figure 17. The wheelsslip a little in the mud and don’t move forward as fast as they doon the pavement. The wheel that enters the mud first getsslowed down a little, but the other wheel on that axle continuesat the original speed. The difference in speed between the twowheels then causes the wheel axle to turn, so the car turns alittle. Light waves behave in the same way.Imagine again a light wave traveling at an angle from air intowater. The first part of the wave to enter the water is slowed, just asthe car wheel that first hit the mud was slowed. The rest of the wavekeeps slowing down as it moves from the air into the water. As longas one part of the light wave is moving faster than the rest of thewave, the wave continues to bend.Figure 16 A light ray is bent asit slows down traveling from airinto water.Figure 17 An axle turns asthe wheels cross the boundarybetween pavement and mud.Predict how the axle would turnif the wheels were going from mudto pavement.Convex and Concave LensesDo you like photographing your friends andfamily? Have you ever watched a bird throughbinoculars or peered at something tiny through amagnifying glass? All of these activities involvethe use of lenses. A lens is a transparent objectwith at least one curved side that causes light tobend. The amount of bending can be controlledby making the sides of the lenses more or lesscurved. The more curved the sides of a lens are,the more light will be bent after it enters the lens.SECTION 3 Refraction and Lenses 563Richard Megna/Fundamental Photographs

Figure 18 A convexlens forms an image thatdepends on the distancefrom the object to thelens.Optical axisFocal pointLight rays that areparallel to the optical axisare bent so they passthrough the focal point.Focal lengthObjectOptical axisImageOptical axisObjectImageOne focal lengthOne focal lengthTwo focal lengthsIf the object is more than two focal lengthsfrom the lens, the image formed is smaller thanthe object and inverted.If the object is closer to the lensthan one focal length, the imageformed is enlarged and upright.Convex Lenses A lens that is thicker in the center than at theedges is a convex lens. In a convex lens, light rays traveling parallelto the optical axis are bent so they pass through the focalpoint, as shown in Figure 18A. The more curved the lens is, thecloser the focal point is to the lens, and so the shorter the focallength of the lens is. Because convex lenses cause light waves tomeet, they also are called converging lenses.The image formed by a convex lens is similar to the imageformed by a concave mirror. For both, the type of imagedepends on how far the object is from the mirror or lens. Lookat Figure 18B. If the object is farther than two focal lengths fromthe lens, the image seen through the lens is inverted and smallerthan the object.How does the focal length of a convex lenschange if the lens becomes more curved?If the object is closer to the lens than one focal length, thenthe image formed is right-side up and larger than the object, asshown in Figure 18C. A magnifying glass forms an image in thisway. As long as the magnifying glass is less than one focal lengthfrom the object, you can make the image appear larger by movingthe magnifying glass away from the object.564 CHAPTER 19 Light, Mirrors, and Lenses

Concave Lenses A lens that is thicker at the edgesthan in the middle is a concave lens. A concave lensalso is called a diverging lens. Figure 19 shows howlight rays traveling parallel to the optical axis are bentafter passing through a concave lens.A concave lens causes light rays to diverge, so lightrays are not brought to a focus. The type of image thatis formed by a concave lens is similar to one that isformed by a convex mirror. The image is upright andsmaller than the object.Optical axisTotal Internal ReflectionWhen you look at a glass window, you sometimes can seeyour reflection. You see a reflection because some of the lightwaves reflected from you are reflected back to your eyes whenthey strike the window. This is an example of a partial reflection—onlysome of the light waves striking the window arereflected. However, sometimes all the light waves that strike theboundary between two transparent materials can be reflected.This process is called total internal reflection.The Critical Angle To see how total internal reflectionoccurs, look at Figure 20. Light travels faster in air than in water,and the refracted beam is bent away from the normal. As theangle between the incident beam and the normal increases, therefracted beam bends closer to the air-water boundary. At thesame time, more of the light energy striking the boundary isreflected and less light energy passes into the air.If a light beam in water strikes the boundary so that theangle with the normal is greater than an angle called the criticalangle, total internal reflection occurs. Then all the light wavesare reflected at the air-water boundary, just as if a mirror werethere. The size of the critical angle depends on the two materialsinvolved. For light passing from water to air, the critical angleis about 48 degrees.Figure 19 A concave lenscauses light rays traveling parallelto the optical axis to diverge.Figure 20 When a light beampasses from one medium toanother, some of its energy isreflected (red) and some isrefracted (blue).AirNormalRefractedbeamAs the incident beam makes a largerangle with the normal, less light energyis refracted, and more is reflected.At the criticalangle, all thelight is reflected.IncidentbeamReflectedbeamWaterSECTION 3 Refraction and Lenses 565

CladdingPlastic fiberLight rayFigure 21 An optical fiber ismade of materials that cause totalinternal reflection to occur. A lightbeam can travel for many kilometersthrough an optical fiber andlose almost no energy.Optical Fibers Optical fibers are thin, flexible, transparentfibers. An optical fiber is like a light pipe. Even if the fiber is bent,light that enters one end of the fiber comes out the other end.Total internal reflection makes light transmission inoptical fibers possible. A thin fiber of glass or plastic is coveredwith another material called cladding in which lighttravels faster. When light strikes the boundary between thefiber and the cladding, total internal reflection can occur. Inthis way, the beam bounces along inside the fiber as shown inFigure 21.Optical fibers are used most commonly in the communicationsindustry. For example, television programs, computerinformation, and phone conversations can be coded into lightsignals. These signals then can be sent from one place to anotherusing optical fibers. Because of total internal reflection, signalscan’t leak from one fiber to another and interfere with others.As a result, the signal is transmitted clearly. One optical fiberthe thickness of a human hair can carry thousands of phoneconversations.SummaryThe•Refraction of LightLight travels at different speeds in different•materials.Refraction occurs when light changes speedas it travels from one material into another.•Convex and Concave LensesA lens is a transparent object with at least one•curved side that causes light to bend.A convex lens is thicker in the center than at•the edges and causes light waves to converge.A concave lens is thinner in the center than atthe edges and causes light waves to diverge.•Total Internal ReflectionTotal internal reflection occurs at the boundarybetween two transparent materials when•light is completely reflected.Optical fibers use total internal reflection totransmit information over long distances withlight waves.Self Check1. Compare the image formed by a concave lens and theimage formed by a convex mirror.2. Explain whether you would use a convex lens or aconcave lens to magnify an object.3. Describe the image formed by convex lens if an objectis less than one focal length from the lens.4. Describe how light rays traveling parallel to the opticalaxis are bent after they pass through a convex lens.5. Infer If the speed of light were the same in all materials,would a lens cause light rays to bend?6. Think Critically A light wave is bent more when ittravels from air to glass than when it travels from air towater. Is the speed of light greater in water or in glass?Explain.7. Calculate Time If light travels at 300,000 km/s andEarth is 150 million km from the Sun, how long does ittake light to travel form the Sun to Earth?566 CHAPTER 19 Light, Mirrors, and Lensesips.msscience.com/self_check_quiz

Using Mirrors and LensesMicroscopesFor almost 500 years, lenses have been used to observeobjects that are too small to be seen with the unaided eye. Thefirst microscopes were simple and magnified less than 100times. Today, a compound microscope like the one in Figure 22uses a combination of lenses to magnify objects by as much as2,500 times.Figure 22 also shows how a microscope forms an image. Anobject, such as an insect or a drop of water from a pond, isplaced close to a convex lens called the objective lens. This lensproduces an enlarged image inside the microscope tube. Thelight rays from that image then pass through a second convexlens called the eyepiece lens. This lens further magnifies theimage formed by the objective lens. By using two lenses, a muchlarger image is formed than a single lens can produce.Figure 22 A compound microscopeuses lenses to magnify objects.■ Explain how microscopesmagnify objects.■ Explain how telescopes makedistant objects visible.■ Describe how a camera works.Microscopes and telescopes are usedto view parts of the universe thatcan’t be seen with the unaided eye.Review Vocabularyretina: region on the inner surfaceof the back of the eye thatcontains light-sensitive cellsNew Vocabulary•refracting telescopereflecting telescopeA compound microscopeoften has more than oneobjective lens—eachproviding a differentmagnification. A lightunderneath the objectivelens makes the imagebright enough to seeclearly.Eyepiece lensImage formedby objective lensObjective lensThe objective lensin a compoundmicroscope formsan enlargedimage, which isthen magnified bythe eyepiece lens.Object 567

Forming an Imagewith a LensProcedure1. Fill a glass test tube withwater and seal it with astopper.2. Write your name on a10-cm 10-cm card.Lay the test tube on thecard and observe theappearance of your name.3. Hold the test tube about1 cm above the card andobserve the appearanceof your name throughit again.4. Observe what happens toyour name as you slowlymove the test tube awayfrom the card.Analysis1. Is the water-filled test tubea concave or a convex lens?2. Compare the imagesformed when the test tubewas close to the card andfar from the card.ObjectivelensTelescopesJust as microscopes are used to magnify very small objects,telescopes are used to examine objects that are very far away.The first telescopes were made at about the same time as the firstmicroscopes. Much of what is known about the Moon, the solarsystem, and the distant universe has come from images andother information gathered by telescopes.Refracting Telescopes The simplest refracting telescopesuse two convex lenses to form an image of a distant object. Justas in a compound microscope, light passes through an objectivelens that forms an image. That image is then magnified by aneyepiece, as shown in Figure 23.An important difference between a telescope and a microscopeis the size of the objective lens. The main purpose of atelescope is not to magnify an image. A telescope’s main purposeis to gather as much light as possible from distant objects. Thelarger an objective lens is, the more light can enter it. This makesimages of faraway objects look brighter and more detailed whenthey are magnified by the eyepiece. With a large enough objectivelens, it’s possible to see stars and galaxies that are manytrillions of kilometers away. Figure 23 also shows the largestrefracting telescope ever made.The refractingtelescope at theYerkes Observatory inWisconsin has thelargest objective lensin the world. It has adiameter of about 1 m.How does a telescope’s objective lens enabledistant objects to be seen?Figure 23 Refractingtelescopes use a largeobjective lens to gather lightfrom distant objects.A refracting telescope is madefrom an objective lens and aneyepiece. The objective lensforms an image that is magnifiedby the eyepiece.Eyepiecelens568 CHAPTER 19 Light, Mirrors, and LensesS0

Figure 24 Reflecting telescopesgather light by using a concavemirror.Eyepiece lensesPlane mirrorLight entering the telescope tubeis reflected by a concave mirroronto the secondary mirror. An eyepieceis used to magnify the imageformed by the concave mirror.The Keck telescope in Mauna Kea,Hawaii, is the largest reflectingtelescope in the world.Concave mirrorReflecting Telescopes Refracting telescopes have size limitations.One problem is that the objective lens can be supportedonly around its edges. If the lens is extremely large, it cannot besupported enough to keep the glass from sagging slightly underits own weight. This causes the image that the lens forms tobecome distorted.Reflecting telescopes can be made much larger than refractingtelescopes. Reflecting telescopes have a concave mirrorinstead of a concave objective lens to gather the light from distantobjects. As shown in Figure 24, the large concave mirrorfocuses light onto a secondary mirror that directs it to the eyepiece,which magnifies the image.Because only the one reflecting surface on the mirror needsto be made carefully and kept clean, telescope mirrors are lessexpensive to make and maintain than lenses of a similar size.Also, mirrors can be supported not only at their edges but alsoon their backsides. They can be made much larger without saggingunder their own weight. The Keck telescope in Hawaii,shown in Figure 24, is the largest reflecting telescope in theworld. Its large concave mirror is 10 m in diameter, and is madeof 36 six-sided segments. Each segment is 1.8 m in size and thesegments are pieced together to form the mirror.The First TelescopesA Dutch eyeglass maker,Hans Lippershey, constructeda refracting telescopein 1608 that had amagnification of 3. In 1609Galileo built a refractingtelescope with a magnificationof 20. By 1668, thefirst reflecting telescopewas built by Isaac Newtonthat had a metal concavemirror with a diameter ofabout 5 cm. More than acentury later, WilliamHerschel built the firstlarge reflecting telescopeswith mirrors as large as50 cm. Research the historyof the telescope andmake a timeline showingimportant events.SECTION 4 Using Mirrors and Lenses 569

ObjectDiaphragmLensFigure 25 A camera uses aconvex lens to form an image on apiece of light-sensitive film. Theimage formed by a camera lens issmaller than the object and isinverted.ShutterCamerasYou probably see photographsImage taken by cameras almost every day. Atypical camera uses a convex lens toform an image on a section of film,just as your eye’s lens focuses animage on your retina. The convexFilmlens has a short focal length, so itforms an image that is smaller thanthe object and inverted on the film.Look at the camera shown inFigure 25. When the shutter is open,the convex lens focuses an image on apiece of film that is sensitive to light. Light-sensitive film containschemicals that undergo chemical reactions when light hitsit. The brighter parts of the image affect the film more than thedarker parts do.What type of lens does a camera use?If too much light strikes the film, the image formed on thefilm is overexposed and looks washed out. On the other hand, iftoo little light reaches the film, the photograph might be toodark. To control how much light reaches the film, many camerashave a device called a diaphragm. The diaphragm is opened tolet more light onto the film and closed to reduce the amount oflight that strikes the film.Topic: LasersVisit ips.msscience.com for Weblinks to information about uses forlasers.Activity Make a table listing differenttypes of lasers and how theyare used.LasersPerhaps you’ve seen the narrow, intense beams of laser lightused in a laser light show. Intense laser beams are also used fordifferent kinds of surgery. Why can laser beams be so intense?One reason is that a laser beam doesn’t spread out as much asordinary light as it travels.Spreading Light Beams Suppose you shine a flashlight ona wall in a darkened room. The size of the spot of light on thewall depends on the distance between the flashlight and the wall.As the flashlight moves farther from the wall, the spot of lightgets larger. This is because the beam of light produced by theflashlight spreads out as it travels. As a result, the energy carriedby the light beam is spread over an increasingly larger area as thedistance from the flashlight gets larger. As the energy is spreadover a larger area, the energy becomes less concentrated and theintensity of the beam decreases.570 CHAPTER 19 Light, Mirrors, and Lenses

Using Laser Light Laser light is differentfrom the light produced by the flashlight inseveral ways, as shown in Figure 26. One differenceis that in a beam of laser light, thecrests and troughs of the light waves overlap,so the waves are in phase.Because a laser beam doesn’t spread out asmuch as ordinary light, a large amount ofenergy can be applied to a very small area.This property enables lasers to be used forcutting and welding materials and as areplacement for scalpels in surgery. Lessintense laser light is used for such applicationsas reading and writing to CDs or ingrocery store bar-code readers. Surveyors andbuilders use lasers to measure distances,angles, and heights. Laser beams also are usedto transmit information through space orthrough optical fibers.Figure 26 Laser light is different from the lightproduced by a lightbulb.The light from a bulb contains waves with many differentwavelengths that are out of phase and traveling indifferent directions.The light from a laser contains waves with only onewavelength that are in phase and traveling in thesame direction.SummaryMicroscopes,•Telescopes, and CamerasA compound microscope uses an objectivelens and an eyepiece lens to form an enlarged•image of an object.A refracting telescope contains a large objectivelens to gather light and a smaller eyepiecelens to magnify the image.•A reflecting telescope uses a large concavemirror to gather light and an eyepiece lens to•magnify the image.The image formed by a telescope becomesbrighter and more detailed as the size of the•objective lens or concave mirror increases.A camera uses a convex lens to form an imageon light-sensitive film.•Laser LightLight from a laser contains light waves thatare in phase, have only one wavelength, and•travel in the same direction.Because laser light does not spread out muchas it travels the energy it carries can beapplied over a very small area.Self Check1. Explain why the concave mirror of a reflecting telescopecan be made much larger than the objective lensof a refracting telescope.2. Describe how a beam of laser light is different than thebeam of light produced by a flashlight.3. Explain why the objective lens of a refracting telescopeis much larger than the objective lens of a compoundmicroscope.4. Infer how the image produced by a compound microscopewould be different if the eyepiece lens wereremoved from the microscope.5. Think Critically Explain why the intensity of the lightin a flashlight beam decreases as the flashlight movesfarther away.6. Calculate Image Size The size of an image is relatedto the magnification of an optical instrument by thefollowing formula:Image size magnification object sizeA blood cell has a diameter of 0.001 cm. How large isthe image formed by a microscope with a magnificationof 1,000?ips.msscience.com/self_check_quizSECTION 4 Using Mirrors and Lenses 571

Goals■ Measure the imagedistance as the objectdistance changes.■ Observe the type ofimage formed as theobject distancechanges.Possible Materialsconvex lensmodeling claymeterstickflashlightmasking tape20-cm square piece ofcardboard with a whitesurfaceSafety PrecautionsImage Formationby a Convex LensReal-World QuestionThe type of image formed by a convex lens, also called a converginglens, is related to the distance of the object from the lens. This distanceis called the object distance. The location of the image also isrelated to the distance of the object from the lens. The distance fromthe lens to the image is called the image distance. How are the imagedistance and object distance related for a convex lens?Convex Lens DataObjectDistance (m)ImageDistance (m)Do not write in this book.Image TypeProcedure1. Design a datatable to recordyour data. Makethree columnsin your table—one columnfor the object distance,another forthe image distance,and the third for the type of image.2. Use the modeling clay to make the lens stand upright on the lab table.3. Form the letter F on the glass surface of the flashlight withmasking tape.4. Turn on the flashlight and place it 1 mfrom the lens. Position the flashlight sothe flashlight beam is shining throughthe lens.5. Record the distance from the flashlightto the lens in the object distancecolumn in your data table.6. Hold the cardboard vertically upright onthe other side of the lens, and move itback and forth until a sharp image of theletter F is obtained.572 CHAPTER 19 Light, Mirrors, and Lenses

7. Measure the distance of the card from the lens using the meterstick, andrecord this distance in the Image Distance column in your data table.8. Record in the third column of your data table whether the image is upright orinverted, and smaller or larger.9. Repeat steps 4 through 8 for object distances of 0.50 m and 0.25 m and recordyour data in your data table.Analyze Your Data1. Describe any observed relationship between the object distance, and theimage type.2. Identify the variables involved in determining the image type for aconvex lens.Conclude and Apply1. Explain how the image distance changedas the object distance decreased.2. Identify how the image changed as the objectdistance decreased.3. Predict what would happen to the size of theimage if the flashlight were much farther awaythan 1 m.Demonstrate this lab to a third-grade classand explain how it works. For more help,refer to the Science Skill Handbook.LAB 573

SOMETIMESGREATDISCOVERIESHAPPEN BYACCIDENT!EyeglassesInventorUnknown“It is not yet twenty years since the artof making spectacles, one of the mostuseful arts on Earth, was discovered.I, myself, have seen and conversed with theman who made them first.”This quote from an Italian monk datesback to 1306 and is one of the first historicalrecords to refer to eyeglasses. Unfortunately,the monk, Giordano, never actually namedthe man he met. Thus, the inventor of eyeglassesremains unknown.The mystery exists, in part, because differentcultures in different places used sometype of magnifying tool to improve theirvision. For example, a rock-crystal lens, madeby early Assyrians who lived 3,500 years agoin what is now Iraq, may have been used toimprove vision. About 2,000 years ago, theRoman writer Seneca looked through a glassglobe of water to make the letters appear biggerin the books he read. By the tenth century,glasses had been invented in China, butthey were used to keep away bad luck, not toimprove vision.In the mid 1400s in Europe, eyeglassesbegan to appear in paintings of scholars,clergy, and the upper classes—eyeglasseswere so expensive that only the rich couldafford them. In the early 1700s, for example,This Italian engraving from the 1600sshows some different types of glasses.glasses cost roughly $200, which is comparableto thousands of dollars today. By the mid-1800s, improvements in manufacturingtechniques made eyeglasses much lessexpensive to make, and thus this importantinvention became widely available to peopleof all walks of life.How Eyeglasses WorkEyeglasses are used to correct farsightednessand nearsightedness, as well as othervision problems. The eye focuses light rays toform an image on a region called the retinaon the back of the eye. Farsighted peoplehave difficulty seeing things close up becauselight rays from nearby objects do not convergeenough to form an image on the retina.This problem can be corrected by using convexlenses that cause light rays to convergebefore they enter the eye. Nearsighted peoplehave problems seeing distant objectsbecause light rays from far-away objects arefocused in front of the retina. Concave lensesthat cause light rays to diverge are used tocorrect this vision problem.Research In many parts of the world, people haveno vision care, and eye diseases and poor vision gountreated. Research the work of groups that bring eyecare to people.For more information, visitips.msscience.com/oopsThe Stapleton Collection/Bridgeman Art Library

Properties of Light1. Light waves can be absorbed, reflected, ortransmitted when they strike an object.2. The color of an object depends on thewavelengths of light reflected by theobject.Reflection and Mirrors1. Light reflected from the surface of an objectobeys the law of reflection—the angle ofincidence equals the angle of reflection.2. Concave mirrors cause light waves to converge,or meet. Convex mirrors cause lightwaves to diverge, or spread apart.Refraction and Lenses1. Light waves bend, or refract, when theychange speed in traveling from onemedium to another.2. A convex lens causes light waves to converge,and a concave lens causes light wavesto diverge.Using Mirrors and Lenses1. A compound microscope uses a convexobjective lens to form an enlarged imagethat is further enlarged by an eyepiece.2. A refracting telescope uses a large objectivelens and an eyepiece lens to form an imageof a distant object.3. A reflecting telescope uses a large concavemirror that gathers light and an eyepiecelens to form an image of a distant object.4. Cameras use a convex lens to form animage on light-sensitive film.Copy and complete the following concept map.Lightis anis reflected byis refracted bythat cantravel inthat canbethat canbeips.msscience.com/interactive_tutorCHAPTER STUDY GUIDE 575

concave lens p. 565convex lens p. 564focal length p. 558focal point p. 558law of reflection p. 555Complete each statement using a word or wordsfrom the vocabulary list above.1. A _____ is the material in which a lightwave travels.2. A narrow beam of light that travels in astraight line is a _____.3. The _____ is the distance from a lens or amirror to the focal point.4. Light rays traveling parallel to the opticalaxis of a convex lens are bent so they passthrough the _____.5. A transparent object with at least onecurved surface that causes light waves tobend is a _____.6. A _____ is thicker in the center than it is atthe edges.7. A _____ uses a large concave mirror togather light from distant objects.Choose the word or phrase that best answers thequestion.8. Light waves travel the fastest through whichof the following?A) air C) waterB) diamond D) a vacuum9. Which of the following determines thecolor of light?A) a prism C) its wavelengthB) its refraction D) its incidence576 CHAPTER REVIEWlens p. 563light ray p. 550medium p. 551reflecting telescope p. 569refracting telescope p. 56810. If an object reflects red and green light,what color does the object appear to be?A) yellow C) greenB) red D) purple11. If an object absorbs all the light that hitsit, what color is it?A) white C) blackB) blue D) green12. What type of image is formed by a planemirror?A) upright C) magnifiedB) inverted D) all of these13. How is the angle of incidence related tothe angle of reflection?A) It’s greater. C) It’s the same.B) It’s smaller. D) It’s not focused.14. Which of the following can be used tomagnify objects?A) a concave lens C) a convex mirrorB) a convex lens D) all of these15. Which of the following describes the lightwaves that make up laser light?A) same wavelengthB) same directionC) in phaseD) all of these16. What is an object that reflects some lightand transmits some light called?A) colored C) opaqueB) diffuse D) translucent17. What is the main purpose of the objectivelens or concave mirror in a telescope?A) invert images C) gather lightB) reduce images D) magnify images18. Which of the following types of mirrorcan form an image larger than the object?A) convex C) planeB) concave D) all of theseips.msscience.com/vocabulary_puzzlemaker

19. Diagram Suppose you can see a person’s eyesin a mirror. Draw a diagram to determinewhether or not that person can see you.20. Determine A singer is wearing a blue outfit.What color spotlights could be used tomake the outfit appear to be black?21. Form a hypothesis to explain why sometimesyou can see two images of yourselfreflected from a window at night.22. Explain why a rough surface, such as a road,becomes shiny in appearance and a betterreflector when it is wet.23. Infer An optical fiber is made of a materialthat forms the fiber and a different materialthat forms the outer covering. For totalinternal reflection to occur, how does thespeed of light in the fiber compare withthe speed of light in the outer covering?Use the table below to answer question 24.Magnification by a Convex LensObject Distance (cm)Magnification25 4.0030 2.0040 1.0060 0.50100 0.2524. Use a Table In the table above, the objectdistance is the distance of the object fromthe lens. The magnification is the imagesize divided by the object size. If the focallength of the lens is 20 cm, how does thesize of the image change as the object getsfarther from the focal point?25. Calculate What is the ratio of the distanceat which the magnification equals 1.00 tothe focal length of the lens?ips.msscience.com/chapter_review26. Oral Presentation Investigate the types ofmirrors used in fun houses. Explain howthese mirrors are formed, and why theyproduce distorted images. Demonstrateyour findings to your class.27. Reverse Writing Images are reversed left toright in a plane mirror. Write a note to afriend that can be read only in a planemirror.28. Design an experiment to determine the focallength of a convex lens. Write a reportdescribing your experiment, including adiagram.Use the graph below to answer questions 29 and 30.Image Distance (cm)504030201010 20 30 40 50Object Distance (cm)29. Image Position The graph shows how thedistance of an image from a convexlens is related to the distance of theobject from the lens. How does theposition of the image change as theobject gets closer to the lens?30. Magnification The magnification ofthe image equals the image distancedivided by the object distance. At whatobject distance does the magnificationequal 2?CHAPTER REVIEW 577

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.1. Which of the following describes an objectthat allows no light to pass through it?A. transparent C. opaqueB. translucent D. diffuse2. Which statement is always true about theimage formed by a concave lens?A. It is upside down and larger than theobject.B. It is upside down and smaller than theobject.C. It is upright and larger than the object.D. It is upright and smaller than the object.Use the figure below to answer questions 3 and 4.6. What does a refracting telescope use toform an image of a distant object?A. two convex lensesB. a concave mirror and a plane mirrorC. two concave lensesD. two concave mirrors7. Through which of the following does lighttravel the slowest?A. air C. waterB. diamond D. vacuum8. What is the bending of a light wave due toa change in speed?A. reflection C. refractionB. diffraction D. transmissionUse the figure below to answer questions 9 and 10.Image3. Which of the following describes theprocess occurring in the upper panel of thefigure?A. refractionB. diffuse reflectionC. regular reflectionD. total internal reflection4. The surface in the lower panel of the figurewould be like which of the following?A. a mirror C. a sheet of paperB. waxed paper D. a painted wall5. Why does a leaf look green?A. It reflects green light.B. It absorbs green light.C. It reflects all colors of light.D. It reflects all colors except green.MirrorWall9. If the girl is standing 1 m from the mirror,where will her image seem to be located?A. 2 m behind the mirrorB. 1 m behind the mirrorC. 2 m in front of the mirrorD. 1 m in front of the mirror10. Which of the following describes theimage of the girl formed by the planemirror?A. It will be upside down.B. It will be in front of the mirror.C. It will be larger than the girl.D. It will be reversed left to right.578 STANDARDIZED TEST PRACTICE

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.11. Light travels slower in diamond than inair. Explain whether total internal reflectioncould occur for a light wave travelingin the diamond toward the diamond’ssurface.Use the figure below to answer question 12.Record your answers on a sheet of paper.18. Explain why you can see the reflection oftrees in the water of a lake on a calm day,but not a very windy day.19. Describe how total internal reflectionenables optical fibers to transmit lightover long distances.20. What happens when a source of light isplaced at the focal point of a concave mirror?Give an example.Use the illustration below to answer question 21.Optical axisOptical axisFocal point12. Identify the type of mirror shown in thefigure and describe the image this mirrorforms.13. Under white light the paper of this pagelooks white and the print looks black.What color would the paper and the printappear to be under red light?14. A light ray strikes a plane mirror such thatthe angle of incidence is 30°. What is theangle between the light ray and the surfaceof the mirror?15. Contrast the light beam from a flashlightand a laser light beam.16. An actor on stage is wearing a magentaoutfit. Explain what color the outfit wouldappear in red light, in blue light, and ingreen light.17. To use a convex lens as a magnifying lens,where must the object be located?Focal length21. Describe how the position of the focalpoint changes as the lens becomes flatterand less curved.22. Compare the images formed by a concavemirror when an object is between thefocal point and the mirror and when anobject is beyond the focal point.23. Explain why increasing the size of theconcave mirror in a reflecting telescopeimproves the images formed.Organize Your Main Points For essay questions, spend a fewminutes listing and organizing the main points that you plan todiscuss. Make sure to do all of this work on your scratch paper,not your answer sheet.Question 19 Organize your discussion points by first listingwhat you know about optical fibers and total internal reflection.ips.msscience.com/standardized_testSTANDARDIZED TEST PRACTICE 579