13.1 The Behavior of Light 13.2 Light and Color 13.3 Producing Light 13.4 Using Light That Inner

BIG Idea

Science Journal

Visible light waves are electro-magnetic waves that can bedetected by the human eye.

13.1 The Behavior of LightLight waves

change direction when theyare reflected or when theychange speed.

13.2 Light and ColorLight waves of

different wavelengths or com-binations of wavelengthscause the human eye to detectdifferent colors.

13.3 Producing LightHeating a tung-

sten filament or passing a cur-rent through a gas are commonways of producing light.

13.4 Using Light

Light can be usedto form three-dimensionalimages and to transmit infor-mation in optical fibers.

That Inner GlowSome organisms, like thissquid, can produce light.The production of light byorganisms is called biolumi-nescence and results from a chemical reaction. Bio-luminescent organismsglow to lure prey, to attracta mate, to coordinate groupmovements, and to evadepredators.

Find other examples of livingorganisms that give off light.

MAIN Idea

MAIN Idea

MAIN Idea

MAIN Idea

Brandon Cole

383

Light Transmission Makethe following Foldable to helpidentify the characteristics of

opaque, translucent, and transparent objects.

Fold a vertical sheetof paper from side toside. Make the frontedge about 1.25 cmshorter than theback edge.

Turn lengthwiseand fold into thirds.

Unfold and cut only the top layeralong both folds to make three tabs.

Label each tab as shown.

Find Main Ideas As you read this chapter, listthe characteristics of opaque, translucent, andtransparent objects.

STEP 4

STEP 3

STEP 2

STEP 1

Rainbows of LightLight passing through a prism can produceexciting patterns of color. Imagine what yoursurroundings would look like now if humanscould see only shades of gray instead of dis-tinct colors. The ability to see color dependson the cells in your eyes that are sensitive todifferent wavelengths of light. What color isthe light produced by a flashlight or the Sun?

1. In a darkened room, shine a flashlightthrough a glass prism. Project the result-ing colors onto a white wall or ceiling.

2. In a darkened room, shine a flashlightover the surface of some water withdishwashing liquid bubbles in it. Whatdo you see?

3. Aim a flashlight at the surface of acompact disc.

4. Think Critically How did your observa-tions in each case differ? Explain whereyou think the colors came from.

Start-Up Activities

Preview this chapter’s contentand activities at gpscience.com

Opaque TransparentTranslucent

383Brandon Cole

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384 CHAPTER 13 Light

Light and Matter Look around your darkened room at night. After your eyes

adjust to the darkness, you begin to recognize some familiarobjects. You know that some of the objects are brightly colored,but they look gray or black in the dim light. Turn on the light,and you clearly can see all the objects in the room, includingtheir colors. What you see depends on the amount of light in theroom and the color of the objects. For you to see an object, itmust reflect some light back to your eyes.

Opaque, Transparent, and Translucent Objects canabsorb light, reflect light, and transmit light—allow light topass through them. The type of matter in an object determinesthe amount of light it absorbs, reflects, and transmits. Forexample, the opaque (oh PAYK) material in the candleholderin Figure 1A only absorbs and reflects light—no light passesthrough it. As a result, you cannot see the candle inside.Materials that allow some light to pass through them, like thematerial of the candleholder in Figure 1B, are described astranslucent (trans LEW sunt). You cannot see clearly throughtranslucent materials.

Transparent materials like the candleholder in Figure 1Ctransmit almost all the light striking them, so you can seeobjects clearly through them. Only a small amount of light isabsorbed and reflected.

The Behavior of Light

Figure 1 These candleholdershave different light-transmittingproperties.

Reading Guide

■ Describe how light waves interactwith matter.

■ Explain the difference betweenregular and diffuse reflection.

■ Define the index of refractionof a material.

■ Explain why a prism separateswhite light into different colors.

The images you see every day are dueto the behavior of light waves.

Review Vocabularyvisible light: an electromagneticwave with wavelengths betweenabout 400 and 750 billionths of ameter

Vocabulary

• opaque

• translucent

• transparent

• index of refraction

• mirage

Opaque

Translucent

Transparent

Mark Burnett

SECTION 1 The Behavior of Light 385

Reflection of LightJust before you left for

school this morning, did youtake a glance in a mirror tocheck your appearance? For youto see your reflection in the mir-ror, light had to reflect off you,hit the mirror, and reflect off themirror into your eye. Reflectionoccurs when a light wave strikesan object and bounces off.

The Law of ReflectionBecause light behaves as awave, it obeys the law of reflec-tion, as shown in Figure 2. According to the law of reflection, theangle at which a light wave strikes a surface is the same as theangle at which it is reflected. Light reflected from any surface—a mirror or a sheet of paper—follows this law.

Regular and Diffuse Reflection Why can you see yourreflection in a store window but not in a brick wall? The answerhas to do with the smoothness of the surfaces. A smooth, evensurface like that of a pane of glass produces a sharp image byreflecting parallel light waves in only one direction. Reflection oflight waves from a smooth surface is regular reflection. A brickwall has an uneven surface that causes incoming parallel lightwaves to be reflected in many directions, as shown in Figure 3.Reflection of light from a rough surface is diffuse reflection.

What are some more examples of objectsthat produce regular or diffuse reflection?

Figure 2 According to the law ofreflection, light is reflected so thatthe angle of incidence alwaysequals the angle of reflection.

Figure 3 This brick wall has anuneven surface, so it produces adiffuse reflection.Explain Use the law of reflectionto explain why a rough surfacecauses parallel light waves to bereflected in many directions.

Mirror

i = angle of incidence

i

r

i

r

r = angle of reflection

Normal

Normal


Roughness of Surfaces Even a surface that appears to besmooth can be rough enough to cause diffuse reflection. Forexample, a metal pot might seem smooth, but at high magnifi-cation, the surface shows rough spots, as shown in Figure 4. Tocause a regular reflection, the roughness of the surface must beless than the wavelengths it reflects.

Refraction of Light What occurs when a light wave passes from one material to

another—from air to water, for example? Refraction is caused bya change in the speed of a wave when it passes from one materialto another. If the light wave is traveling at an angle and the speedthat light travels is different in the two materials, the wave will bebent, or refracted.

How does refraction occur?

The Index of Refraction The amount of bending that takesplace depends on the speed of light in both materials. The greaterthe difference is, the more the light will be bent as it passes at anangle from one material to the other. Figure 5 shows an exampleof refraction. Every material has an index of refraction—a prop-erty of the material that indicates how much the speed of light inthe material is reduced.

The larger the index of refraction, the more light is sloweddown in the material. For example, because glass has a largerindex of refraction than air, light moves more slowly in glassthan air. Many useful devices like eyeglasses, binoculars, cam-eras, and microscopes form images using refraction.

Figure 4 Although the surfaceof this pot may seem smooth, itproduces a diffuse reflection. Athigh magnification, the surface isseen to be rough.

Figure 5 The spoon looks bentbecause light waves are refractedas they change speed when theypass from the water to the air.

(tl)Bruce Iverson, (tr)Myrleen Cate/Index Stock/PictureQuest, (bl)Stephen Frisch/Stock Boston/PictureQuest

SECTION 1 The Behavior of Light 387

Prisms A sparkling glass prismhangs in a sunny window, refractingthe sunlight and projecting a color-ful pattern onto the walls of theroom. How does the bending oflight create these colors? It occursbecause the amount of bending usu-ally depends on the wavelength ofthe light. Wavelengths of visible lightrange from the longer red waves tothe shorter violet waves. White light,such as sunlight, is made up of thiswhole range of wavelengths.

Figure 6 shows what occurs when white light passes througha prism. The triangular prism refracts the light twice—oncewhen it enters the prism and again when it leaves the prism andreenters the air. Because the longer wavelengths of light arerefracted less than the shorter wavelengths are, red light is bentthe least. As a result of these different amounts of bending, thedifferent colors are separated when they emerge from the prism.Which color of light would you expect to bend the most?

Rainbows Does the light leaving the prism in Figure 6 remindyou of a rainbow? Like prisms, rain droplets also refract light.The refraction of the different wavelengths can cause white lightfrom the Sun to separate into the individual colors of visiblelight, as shown in Figure 7. In a rainbow, the human eye usuallycan distinguish only about seven colors clearly. In order ofdecreasing wavelength, these colors are red, orange, yellow,green, blue, indigo, and violet.

Figure 6 Refraction causes aprism to separate a beam of whitelight into different colors.

Figure 7 As white light passes through the water droplet,different wavelengths are refracted by different amounts.This produces the separate colors seen in a rainbow.

Water droplet

SunlightIncident ray

Observing Refractionin Water Procedure 1. Place a penny at the bot-

tom of a short, opaquecup. Set it on a table infront of you.

2. Have a partner slowly slidethe cup away from you untilyou can’t see the penny.

3. Without disturbing thepenny or the cup and with-out moving your position,have your partner slowlypour water into the cupuntil you can see the penny.

4. Reverse roles and repeatthe experiment.

Analysis 1. What did you observe?

Explain how this is possible.2. In your Science Journal,

sketch the light path fromthe penny to your eyeafter the water was added.

David Parker/Science Photo Library/Photo Researchers


Mirages You might have seen what looks like a pool of water onthe road ahead. As you get closer, the water seems to disappear.Yousaw a mirage, an image of a distant object produced by the refrac-tion of light through air layers of different densities. Mirages resultwhen the air at ground level is much warmer or cooler than the airabove it, as Figure 8 shows. The density of air increases as air cools.Light waves travel slower as the density of air increases, so thatlight travels slower in cooler air. As a result, light waves refract asthey pass through air layers with different temperatures.

gpscience.com/self_check_quiz

Figure 8 Mirages result whenair near the ground is muchwarmer or cooler than the airabove. This causes some light-waves reflected from the object torefract, creating one or more addi-tional images.

MirageWarm air

Cool air

Self Check1. Compare and contrast opaque, transparent, and

translucent materials. Give at least one exampleof each.

2. Discuss why you can see your reflection in a smoothpiece of aluminum foil but not in a crumpled ball of foil.

3. Explain why you are more likely to see a mirage on ahot day than on a mild day.

4. Infer what happens to white light when it passesthrough a prism.

5. Think Critically Decide whether the lens of your eye,a fingernail, your skin, and your tooth are opaque,translucent, or transparent. Explain.

SummaryLight and Matter

• When light waves strike an object, the lightcan be absorbed, reflected, and transmitted.

• The amount of light that is absorbed,reflected, or transmitted depends on thematerial an object is made from.

Reflection of Light

• Light waves always obey the law of reflec-tion—the angle of incidence equals the angleof reflection.

• Regular reflection occurs when the roughness ofa surface is less than the wavelengths reflected.

• Diffuse reflection causes parallel light waves tobe reflected in many directions.

Refraction of Light

• Refraction occurs if a light wave changesspeed in moving from one material to another.

• The index of refraction of a material indicateshow much light slows down in the material.

• In a material, different wavelengths of lightcan be refracted by different amounts.

6. Find an Angle A light ray strikes a mirror at an angleof 42° from the surface of the mirror. What angle doesthe reflected ray make with the normal?

7. Find an Angle A ray of light hits a mirror at 27° fromthe normal. What is the angle between the reflected ray and the normal?

Charles O'Rear/CORBIS


SECTION 2 Light and Color 389

ColorsWhy do some apples appear red, while others look green or

yellow? An object’s color depends on the wavelengths of light itreflects. You know that white light is a blend of all colors of vis-ible light. When a red apple is struck by white light, it reflects redlight back to your eyes and absorbs all of the other colors.Figure 9 shows white light striking a green leaf. Only the greenlight is reflected to your eyes.

Although some objects appear to be black, black isn’t a colorthat is present in visible light. Objects that appear black absorball colors of light and reflect little or no light back to your eye.White objects appear to be white because they reflect all colorsof visible light.

Why does a white object appear white?

Colored Filters Wearing tinted glasses changesthe color of almost everything you look at. If thelenses are yellow, the world takes on a golden glow. Ifthey are rose colored, everything looks rosy.Something similar would occur if you placed a col-ored, clear plastic sheet over this white page. Thepaper would appear to be the same color as the plas-tic. The plastic sheet and the tinted lenses are filters.A filter is a transparent material that transmits one ormore colors of light but absorbs all others. The colorof a filter is the color of the light that it transmits.

Light and ColorReading Guide

■ Explain how you see color.■ Describe the difference between

light color and pigment color.■ Predict what happens when dif-

ferent colors are mixed.

From traffic lights to great works ofart, color plays an important role inyour world.

Review Vocabularyretina: inner layer of the eyecontaining cells that convert lightimages into electrical signals

New Vocabulary

• pigment

Figure 9 This green leaf absorbsall wavelengths of visible lightexcept green.


Looking Through Colored Filters Figure 10 shows whathappens when you look at a colored object through various col-ored filters. In the white light in Figure 10A, a blue cooler looksblue because it reflects only the blue light in the white light strik-ing it. It absorbs the light of all other colors. If you look at thecooler through a blue filter as in Figure 10B, the cooler stilllooks blue because the filter transmits the reflected blue light.Figure 10C shows how the cooler looks when you examine itthrough a red filter.

Why does the blue cooler appear black through ared filter?

Seeing ColorAs you approach a busy intersection, the color of the traffic

light changes from green to yellow to red. On the cross street, thecolor changes from red to green. At a busy intersection, trafficsafety depends on your ability to detect immediate colorchanges. How do you see colors?

Light and the Eye In a healthy eye, light enters and isfocused on the retina, an area on the inside of your eyeball, asshown in Figure 11A. The retina is made up of two types of cellsthat absorb light, as shown in Figure 11B. When these cellsabsorb light energy, chemical reactions convert light energy intonerve impulses that are transmitted to the brain. One type ofcell in the retina, called a cone, allows you to distinguish colorsand detailed shapes of objects. Cones are most effective in day-time vision.

The cooler appears blackthrough a red filter.

The cooler appears blue whenviewed through a blue filter.

The blue cooler is shown inwhite light.

Figure 10 The color of thiscooler seems to change under dif-ferent lighting conditions.

Mark Burnett

Retina

Rod

Cone

Lens


Cones and Rods Your eyes have three types of cones, each ofwhich responds to a different range of wavelengths. Red conesrespond to mostly red and yellow, green cones respond tomostly yellow and green, and blue cones respond to mostly blueand violet. The second type of cell, called a rod, is sensitive todim light and is useful for night vision.

Interpreting Color Why does a bananalook yellow? The light reflected by the

banana causes the cone cells that are sensitive to red and greenlight to send signals to your brain. Your brain would get the samesignal if a mixture of red light and green light reached your eye.Again, your red and green cones would respond, and you wouldsee yellow light because your brain can’t perceive the differencebetween incoming yellow light and yellow light produced bycombining red and green light. The next time you are at a play ora concert, look at the lighting above the stage. Watch how thecolored lights combine to produce effects onstage.

Color Blindness If one or more of your sets of conesdid not function properly, you would not be able to distin-guish between certain colors. About eight percent of menand one-half percent of women have a form of color blind-ness. Most people who are said to be color-blind are nottruly blind to color, but they have difficulty distinguishingbetween a few colors, most commonly red and green.Figure 12 shows a page of a color blindness test. Becausethese two colors are used in traffic signals, drivers andpedestrians must be able to identify them.

Figure 11 Light enters the eyeand focuses on the retina. The twotypes of light-detecting cells thatmake up the retina are calledrods and cones.

Figure 12 Color blindness is aninherited sex-linked condition inwhich certain cones do not func-tion properly. Identify what number you see inthe dots.

(tl)Ralph C. Eagle, Jr./Photo Researchers, (br)Diane Hirsch/Fundamental Photographs


Mixing Colors If you have ever browsed through a paint store, you have

probably seen displays where customers can select paint samplesof almost every imaginable color. The colors are a result of mix-tures of pigments. For example, you might have mixed blue andyellow paint to produce green paint. A pigment is a coloredmaterial that is used to change the color of other substances.The color of a pigment results from the different wavelengths oflight that the pigment reflects.

Mixing Colored Lights From the glowing orange of a sun-set to the deep blue of a mountain lake, all the colors you see canbe made by mixing three colors of light. These three colors—red, green, and blue—are the primary colors of light. They cor-respond to the three different types of cones in the retina ofyour eye. When mixed together in equal amounts, they producewhite light, as Figure 13 shows. Mixing the primary colors indifferent proportions can produce the colors you see.

What are primary colors?

Paint Pigments If you were to mix equal amounts of red,green, and blue paint, would you get white paint? If mixing col-ors of paint were like mixing colors of light, you would, but mix-ing paint is different. Paints are made with pigments. Paintpigments usually are made of chemical compounds such as tita-nium oxide, a bright white pigment, and lead chromate, whichis used for painting yellow lines on highways.

Figure 13 White light is pro-duced when the three primary col-ors of light are mixed.

Color for PhotosynthesisPlant pigments deter-mine the wavelengths oflight for photosynthesis.Leaves usually lookgreen due to the pigmentchlorophyll. Chlorophyllabsorbs most wave-lengths of visible lightexcept green, which itreflects. But not all plantsare green. Research dif-ferent plant pigments tofind how they allow plantspecies to survive indiverse habitats.

Matt Meadows


Self Check1. Identify what colors are reflected and what colors are

absorbed if a white light shines on a red shirt.

2. Discuss how the primary colors of light differ from theprimary pigment colors.

3. Explain why a color-blind person can distinguishamong some colors but not others.

4. Determine why a white fence appears to be white insteadof multicolored if all colors are present in white light.

5. Think Critically Light reflected from an object passesthrough a green filter, then a red filter, and finally ablue filter. What color will the object seem to be?

SummaryColors

• The color of an object is determined by thewavelengths of light it reflects.

• The color of a filter is the color of the lightthe filter transmits.

Seeing Color

• Rod and cone cells are light-sensitive cellsfound in the retina of the human eye.

• Rod cells are sensitive to dim light. Cone cellsenable the human eye to see colors.

• There are three types of cone cells. One typeresponds to red light, another to green light,and another to blue light.

Mixing Colors

• Red, green and blue are the primary lightcolors. Any color can be created by mixingthese primary light colors.

• Any pigment color can be formed by mixingthe primary pigment colors—magenta, cyan,and yellow.

6. Use Percentages In the human eye there are about120,000,000 rods. If 90,000,000 rods trigger at once,what percentage of the total number of rods triggered?

7. Convert Units The wavelengths of a color are meas-ured in nanometers (nm) which is 0.000001 mm.Find the wavelength in mm of a light wave that has a wavelength of 690 nm.

Mixing Pigments You can make any pigment color by mix-ing different amounts of the three primary pigments—magenta(bluish red), cyan (greenish blue), and yellow. In fact, colorprinters use those pigments to make full-color prints like thepages in this book. However, color printers also use black ink toproduce a true black color. A primary pigment’s color dependson the color of light it reflects. Actually, pigments both absorband reflect a range of colors in sending a single color message toyour eye. For example, in white light, the yellow pigmentappears yellow because it reflects yellow, red, orange, and greenlight but absorbs blue and violet light. The color of a mixture oftwo primary pigments is determined by the primary colors oflight that both pigments reflect.

Look at Figure 14. The area in the center where the colors alloverlap appears to be black because the three blended primarypigments absorb all the primary colors of light. Recall that theprimary colors of light combine to produce white light. They arecalled additive colors. However, the primary pigment colorscombine to produce black. Because black results from theabsence of reflected light, the primary pigments are called sub-tractive colors.

Figure 14 The three primarycolors of pigment appear to beblack when they are mixed.




Producing LightReading Guide

■ Explain how incandescent and fluorescent lightbulbs work.

■ Analyze the advantages and disadvantages of different light-ing devices.

■ Explain how a laser producescoherent light.

■ Describe various uses of lasers.

Knowing how different lightingdevices work will help you choosethe right one for your needs.

Review Vocabularyelectron: negatively charged particlefound in an atom

New Vocabulary

• incandescent light

• fluorescent light

• coherent light

• incoherent light

Incandescent Lights Most of the lightbulbs in your house probably produce

incandescent light, which is generated by heating a piece ofmetal until it glows. Inside an incandescent lightbulb is a smallwire coil, called a filament, that usually is made of tungstenmetal. When an electric current flows in the filament, the electricresistance of the metal causes the filament to become hot enoughto give off light. However, about 90% of the energy given off byan incandescent bulb is in the form of thermal energy.

Why does an incandescent lightbulb get hot?

Fluorescent Lights Your house also may have fluorescent (floo RE sunt) lights. A

fluorescent bulb, like the one shown in Figure 15, is filled with a gasat low pressure. The inside of the bulb is coated with phosphorsthat emit visible light when they absorb ultraviolet radiation. The

tube also contains electrodes at eachend. Electrons are given off when theelectrodes are connected in a circuit.When these electrons collide withthe gas atoms, ultraviolet radiation isemitted. The phosphors on theinside of the bulb absorb this radia-tion and give off visible light.

Gas Bulb

Phosphorescent coating

Electrode

Figure 15 Fluorescent light-bulbs do not use filaments.Determine what property of phos-phors makes them useful in fluores-cent bulbs.

SECTION 3 Producing Light 395

Efficient Lighting A fluorescent light uses phosphors toconvert ultraviolet radiation to visible light. Fluorescent lightsuse as little as one fifth the electrical energy to produce the sameamount of light as incandescent bulbs. Fluorescent bulbs alsolast much longer than incandescent bulbs. This higher efficiencycan mean lower energy costs over the life of the bulb. Reducedenergy usage could reduce the amount of fossil fuels burned togenerate electricity, which also decreases the amount of carbondioxide and pollutants released into Earth’s atmosphere.

Fluorescent bulbs are used widely in hospitals, office build-ings, schools, and factories. Compact fluorescent bulbs, whichcan be screwed into traditional lightbulb sockets, have beendeveloped for use in homes.

Neon Lights The vivid, glowing colors of neon lights, such as those shown

in Figure 16, make them a popular choice for signs and eye-catching decorations on buildings. These lighting devices areglass tubes filled with gas, typically neon, and work similarly tofluorescent lights. When an electric current flows through thetube, electrons collide with the gas molecules. In this case, how-ever, the collisions produce visible light. If the tube containsonly neon, the light is bright red. Different colors can be pro-duced by adding other gases to the tube.

What causes the color in a neon light?

Discovering EnergyWaste in LightbulbsProcedure1. Obtain an incandescent

bulb and a fluorescentbulb of identical wattage.

2. Make a heat collector bycovering the top of a foamcup with a piece of plasticfood wrap to make a win-dow. Carefully make asmall hole (diameter lessthan the thermometer’s) inthe side of the cup. Push athermometer through thehole.

3. Measure the temperatureof the air inside the cup.Then, hold the window ofthe tester 1 cm from one ofthe lights for 2 min andmeasure the temperature.

4. Cool the heat collector andthermometer. Repeat step3 using the second bulb.

Analysis 1. What was the temperature

for each bulb? 2. Which bulb appears to give

off more heat? Explain whythis occurs.

Ne

Ne

Ne

Ne

Electron

Light

Figure 16 This neonlight has vivid, glowingcolors.

Ginger Chih/Peter Arnold, Inc.


Sodium-Vapor Lights Sodium-vapor lights often are used for

streetlights and other outdoor lighting.Inside a sodium-vapor lamp is a tube thatcontains a mixture of neon gas, a smallamount of argon gas, and a small amountof sodium metal. When the lamp is turnedon, the gas mixture becomes hot. The hotgases cause the sodium metal to turn tovapor, and the hot sodium vapor emits ayellow-orange glow, as shown in Figure 17.

Tungsten-Halogen Lights Tungsten-halogen lights sometimes are used to create

intensely bright light. These lights have a tungsten filamentinside a quartz bulb or tube. The tube is filled with a gas thatcontains one of the halogen elements, such as fluorine or chlo-rine. The presence of this gas enables the filament to becomemuch hotter than the filament in an ordinary incandescentbulb. As a result, the light is much brighter and also lasts longer.Tungsten-halogen lights sometimes are used on movie sets andin underwater photography.

LasersFrom laser surgery to a laser light show, lasers have become

a large part of the world you live in. A laser’s light begins whena number of light waves are emitted at the same time. To achievethis, a number of identical atoms each must be given the sameamount of energy. When they release their energy, each atomsends off an identical light wave. This light wave is reflectedbetween two facing mirrors at opposite ends of the laser. One ofthe mirrors is coated only partially with reflective material, so itreflects most light but allows some to get through. Some emit-ted light waves travel back and forth between the mirrors manytimes, stimulating other atoms to emit identical light waves also.Figure 18 shows how this process produces a beam of laser light.

How do mirrors help in creating lasers?

Lasers can be made with many different materials, includinggases, liquids, and solids. One of the most common is thehelium-neon laser, which produces a beam of red light. A mix-ture of helium and neon gases sealed in a tube with mirrors atboth ends is excited by a flashtube. The excited atoms then losetheir excess energy by emitting coherent light waves.

Topic: Light PollutionVisit gpscience.com for Web linksto information about sodium vaporlights and light pollution.

Activity Research light pollutionand how it affects astronomers.Determine which types of outdoorlights create more and which cre-ate less light pollution.

Figure 17 Sodium-vapor lightsemit mostly yellow light. Half ofthis photo was taken under sun-light and half was taken undersodium-vapor lighting.

Mark Burnett


Lasers produce light waves that have the same wave-length. Almost all of these waves travel in the samedirection and are in phase. As a result, beams of laser

light can be made more intense than ordinary light. Inmodern eye surgery, shown at the right, lasers are oftenused instead of a traditional scalpel.

When the lightbulb is turned on, energy isabsorbed by the atoms in the rod.These atoms thenre-emit that energy as light waves that are in phaseand have the same wavelength.

B

Most of these waves are reflectedbetween the mirrors located at eachend of the laser. One of the mirrors,however, is only partially reflective,allowing one percent of the lightwaves to pass through it and form a beam.

C

As the waves travel back and forth between the mirrors,they stimulate other atoms in the ruby rod to emit lightwaves. In a fraction of a second, billions of identical waves arebouncing between the mirrors.The waves are emitted fromthe partially reflective mirror in a stream of laser light.

D

Light-producingmaterial

Mirror Mirror

Energy source

The key parts of a laser include a mate-rial that can be stimulated to produce light,such as a ruby rod, and an energy source.In this example, the energy source is a light-bulb that spirals around the ruby rod andemits an intense light.

A

397

Figure 18

VISUALIZING LASERS

Light waves Atoms

Will & Deni McIntyre/Photo Researchers


Coherent Light Lasers produce the narrowbeams of light that zip across the stage andthrough the auditorium during some rock con-certs. Beams of laser light do not spread outbecause laser light is coherent. Coherent light islight of only one wavelength that travels with itscrests and troughs aligned. The beam does notspread out because all the waves travel in the samedirection, as shown in Figure 19A. As a result, theenergy carried by the beam remains concentratedover a small area.

Incoherent Light Light from an ordinary light-bulb is incoherent. Incoherent light can containmore than one wavelength, and its electromag-netic waves are not aligned, as in Figure 19B. Thewaves don’t travel in the same direction, so thebeam spreads out. The energy carried by the lightwaves is spread over a large area, so the intensity ofthe light is much less than that of the laser beam.

Using LasersCompact disc players, surgical tools, and many other useful

devices take advantage of the unique properties of lasers. A laserbeam is narrow and does not spread out as it travels over longdistances. So lasers can apply large amounts of energy to smallareas. In industry, powerful lasers are used for cutting and weld-ing materials. Surveyors and builders use lasers for measuringand leveling. To measure the moon’s orbit with great accuracy,scientists use laser light reflected from mirrors placed on theMoon’s surface. Information also can be coded in pulses of lightfrom lasers. This makes them useful for communications. Intelephone systems, pulses of laser light transmit conversationsthrough long glass fibers called optical fibers.

Lasers in Medicine Lasers are routinely used to removecataracts, reshape the cornea, and repair the retina. In the eyeand other parts of the body, surgeons can use lasers in place ofscalpels to cut through body tissues. The energy from the laserseals off blood vessels in the incision and reduces bleeding.Because most lasers do not penetrate deeply through the skin,they can be used to remove small tumors or birthmarks on thesurface without damaging deeper tissues. By sending laser lightinto the body through an optical fiber, physicians can also treatconditions such as blocked arteries.

Figure 19 Light waves can beeither coherent or incoherent.

These waves are coherentbecause they have the same wave-length and travel with their crestsand troughs aligned.

Incoherent waves such as thesecan contain more than one wave-length, and do not travel with theircrests and troughs aligned.

SECTION 3 Producing Light 399

Self Check1. Explain how light is produced in an ordinary incandes-

cent bulb.

2. Discuss the advantages of using a fluorescent bulbinstead of an incandescent bulb.

3. Describe the difference between coherent and incoher-ent light.

4. Think Critically Which type of lighting device wouldyou use for each of the following needs: an economicallight source in a manufacturing plant, an eye-catchingsign that will be visible at night, and a baseball sta-dium? Explain.

SummaryIncandescent and Fluorescent Lights

• In an incandescent bulb, an electric currentheats a tungsten filament so that it glows.

• The phosphorescent coating on the inside of afluorescent bulb absorbs ultraviolet light andemits visible light.

Other Light Sources

• In a neon tube, red light is produced whenelectrons collide with atoms of neon gas.

• In a sodium-vapor light, sodium metal isvaporized and emits a yellow-orange glow.

• A tungsten-halogen bulb is brighter and hot-ter than an ordinary incandescent bulb.

Lasers

• Laser light is produced when identical atomsare stimulated to emit coherent light.

• A laser beam does not spread, so energy car-ried by the beam can be concentrated in asmall area.

5. Calculate Efficiency A 25-W fluorescent light emits5.0 J of thermal energy each second. What is the effi-ciency of the fluorescent light?

6. Use Percentages If 90 percent of the energy emittedby an incandescent bulb is thermal energy, how muchthermal energy is emitted by a 60-W bulb each second?


Spinning CD

Laser

Lightsensor

Compact Discs Compact discs are plastic discs with reflec-tive surfaces used to store sound, images, and text in digitalform. When a CD is produced, the information is burned intothe surface of the disc with a laser. The laser creates millions oftiny pits in a spiral pattern that starts at the center of the discand moves out to the edge. A CD player, shown in Figure 20,also uses a laser to read the disc. As the laser beam strikes a pitor flat spot, different amounts of light are reflected to a lightsensor. The reflected light is converted to an electric signal thatthe speakers use to create sound.

Figure 20 The blowup showsthe pits (blue) on the bottom sur-face of a CD. A CD player uses alaser to convert the informationon the CD to an electric signal.

Andrew Syred/Science Photo Library/Photo Researchers



Using LightReading Guide

■ Distinguish polarized light fromunpolarized light.

■ Explain how a hologram is made.■ Determine when total internal

reflection occurs.■ Describe the uses of optical

fibers.

Light waves were used to transmit aTV program you watched today, orto send a telephone call to a friend.

Review Vocabularyinterference: occurs when two ormore waves overlap and form a newwave

New Vocabulary

• polarized light

• holography

• total internal reflection

Polarized Light You may have a pair of sunglasses with a sticker on them that

says “polarized.” Do you know what makes them different fromother sunglasses? The difference has to do with the vibrationof light waves that pass through the lenses. You can maketransverse waves in a rope vibrate in any direction—horizontal,vertical, or anywhere in between. Light also is a transverse waveand can vibrate in any direction. In polarized light, however,the waves vibrate in only one direction.

Polarizing Filters If the light passes through a special polar-izing filter, the light becomes polarized. A polarizing filteracts like a group of parallel slits. Only light waves vibrating inthe same direction as the slits can pass through. If a secondpolarizing filter is lined up with its slits at right angles to those

of the first filter, no light can pass through, asFigure 21 shows.

Polarized lenses are useful for reducingglare without interfering with your ability tosee clearly. When light is reflected from ahorizontal surface, such as a lake or a shinycar hood, it becomes partially horizontallypolarized. The lenses of polarizing sun-glasses have vertical polarizing filters thatblock out the reflected light that has beenpolarized horizontally.Wave motion transmitted

Wave motion blocked

If the slats arealigned atright angles toeach other, thewave can’tpass through.

If the slats arein the samedirection, thewave passesthrough.

Figure 21 Slats in a fencebehave like a polarizing filterfor a transverse wave on a rope.

SECTION 4 Using Light 401

Figure 22 Lasers can be used to make holograms like this one.

Topic: HologramsVisit gpscience.com for Web linksto information about holograms.

Activity Make an events-chainconcept map of how a hologram isproduced.

HolographyScience museums often have exhibits where a three-dimen-

sional image seems to float in space, like the one shown inFigure 22. You can see the image from different angles, just asyou would if you viewed the real object. Three-dimensionalimages on credit cards are produced by holography. Holographyis a technique that produces a hologram—a complete three-dimensional photographic image of an object.

Making Holograms Illuminating objects with laser lightproduces holograms. Laser light reflects from the object ontophotographic film. At the same time, a second beam split fromthe laser also is directed at the film. The light from the twobeams creates an interference pattern on the film. The patternlooks nothing like the original object, but when laser light shineson the pattern on the film, a holographic image is produced.

Information in Light An ordinary photographic image cap-tures only the brightness or intensity of light reflected from anobject’s surface, but a hologram records the intensity as well asthe direction. As a result, it conveys more information to youreye than a conventional two-dimensional photograph does, butit also is more difficult to copy. Holographic images are used oncredit cards, identification cards, and on the labels of someproducts to help prevent counterfeiting. Using X-ray lasers,scientists can produce holographic images of microscopicobjects. It may be possible to create three-dimensional views ofbiological cells.

How are holographic images produced?

Larry Mulvehill/Photo Researchers



Optical Fibers When laser light must travel long distances or be sent into

hard-to-reach places, optical fibers often are used. These trans-parent glass fibers can transmit light from one place to another.A process called total internal reflection makes this possible.

Total Internal Reflection Remember what happens whenlight speeds up as it travels from one medium to another. Forexample, when light travels from water to air the direction of thelight ray is bent away from the normal, as shown in Figure 23. Ifthe underwater light ray makes a larger angle with the normal,the light ray in the air bends closer the surface of the water. At acertain angle, called the critical angle, the refracted ray has beenbent so that it is traveling along the surface of the water, asshown in Figure 23. For a light ray traveling from water into air,the critical angle is about 49°.

Figure 23 shows what happens if the underwater light raystrikes the boundary between the air and water at an angle largerthan the critical angle. There is no longer any refraction, and thelight ray does not travel in the air. Instead, the light ray isreflected at the boundary, just as if a mirror were there. Thisbehavior of light is called total internal reflection. Total internalreflection occurs when light traveling from one medium toanother is completely reflected at the boundary between the twomaterials. Then the light ray obeys the law of reflection. For totalinternal reflection to occur, light must travel slower in the firstmedium, and must strike the boundary at an angle greater thanthe critical angle.

How does total internal reflection occur?

Figure 23 A light wave is bentaway from the normal as it passesfrom water to air. At the criticalangle, the refracted wave is travel-ing along the water surface. Atangles greater than the criticalangle, total internal reflectionoccurs.

Air

Normal Normal

Total internalreflection

Critical angleWater

SECTION 4 Using Light 403

Light Pipes Total internal reflection makes light transmissionin optical fibers possible. As shown in Figure 24, light enteringone end of the fiber is reflected continuously from the sides ofthe fiber until it emerges from the other end. Like water movesthrough a pipe, almost no light is lost or absorbed in opticalfibers.

Using Optical Fibers Optical fibers are most often used incommunications. Telephone conversations, television pro-grams, and computer data can be coded in light beams. Signalscan’t leak from one fiber to another and interfere with othermessages, so the signal is transmitted clearly. To send telephoneconversations through an optical fiber, sound is converted intodigital signals consisting of pulses of light by a light-emittingdiode or a laser. Some systems use multiple lasers, each with itsown wavelength, to fit multiple signals into the same fiber.You could send a million copies of the play Romeo and Juliet inone second on a single fiber. Figure 24 shows the size of typicaloptical fibers.

Optical fibers also are used to explore the inside of thehuman body. One bundle of fibers transmits light, whileanother carries the reflected light back to the doctor.

Light

Plastic covering

Glass core

Glass layer

Light rays

Figure 24 Optical fibers make use of total internal reflection.

An optical fiberreflects light so thatit is piped through thefiber without leavingit, except at the ends.

Just one of these optical fiberscan carry thousands of phoneconversations at the same time.

Wire CommunicationAt one time telegraphand telephone communi-cations were transmittedonly through wire lines.Today, optical fiberssometimes are usedinstead of wires to trans-mit communications.Research the history ofwire communication.Create a time line ofwhat you learn.

Paul Silverman/Fundamental Photographs


Self Check1. Explain why polarized sunglasses can reduce the glare

from light reflected from lakes and ponds.

2. Describe why a holographic image is considered to bethree-dimensional.

3. List all the conditions that are necessary for total inter-nal reflection to occur.

4. Discuss how optical fibers are used to transmit tele-phone conversations.

5. Think Critically On a sunny day you are looking at thesurface of a lake through polarized sunglasses. Howcould you use your sunglasses to tell if the lightreflected from the lake is polarized?

SummaryPolarized Light

• Polarized light has light waves that vibrate inonly one direction.

• Polarizing filters block light waves that vibrateat right angles to the direction of the filter.

Holography

• A hologram is produced by interferencebetween laser light reflected from an objectand a second laser beam.

Optical Fibers

• Total internal reflection occurs when light iscompletely reflected at the boundarybetween two materials.

• Total internal reflection will occur when theangle between the light beam and the normalis equal to, or greater than, the critical angle.

• Optical fibers use total internal reflection totransmit light waves over long distances.

Optical ScannersIn supermarkets and many other kinds of stores, a

cashier passes your purchases over a glass window in thecheckout counter or holds a handheld device up to eachitem, like the one in Figure 25. In an instant, the opticalscanner beeps and the price of the item appears on ascreen. An optical scanner is a device that reads intensi-ties of reflected light and converts the information todigital signals. You may have noticed that somewhere oneach item the cashier scans is a pattern of thick and thinstripes called a bar code. An optical scanner detects thepattern and translates it into a digital signal, which goesto a computer. The computer searches its database for a

matching item, finds its price, and sends the information to thecash register.

You may have used another type of optical scanner to con-vert pictures or text into forms you can use in computer pro-grams. With a flatbed scanner, for example, you lay a documentor picture facedown on a sheet of glass and close the cover. Anoptical scanner passes underneath the glass and reads the pat-tern of colors. The scanner converts the pattern to an electronicfile that can be stored on a computer.


Figure 25 Optical scanners likethis one use lasers to find the priceof various products.

6. Calculate Number of Fibers An optical fiber has adiameter of 0.3 mm. How many fibers would beneeded to form a cable with a square cross section, if the cross section was 1.5 cm on a side?

David Young-Wolff/PhotoEdit, Inc.


From a hilltop you can see the reflection of pinetrees and a cabin in the calm surface of a lake.This is possible because some of the light thatreflects off these objects strikes the water’s sur-face and reflects into your eyes. However, youdon’t see a clear, colorful image because muchof the light enters the water rather than beingreflected.

Real-World QuestionHow does water affect the viewer’s image of anobject that is above the water’s surface?

Goals■ Identify reflection of an image in water.■ Identify refraction of an image in water.

Materialslight sourceunsharpened pencilclear rectangular containerwaterclay

Safety Precautions

Procedure1. Fill the container with water.

2. Place the container so that a light source—window or overhead light—reaches it.

3. Stand the pencil on end in the clay and placeit by the container as shown in the figureabove. The pencil must be taller than the levelof the water. Also, place the pencil on thesame side of the container as the light source.

4. Looking down through the surface of thewater from the side opposite the pencil,observe the reflection and refraction of theimage of the pencil.

5. Draw a diagram of the image and labelReflection and Refraction.

6. Repeat steps 4 and 5 two more times, butposition the pencil at two different angles.

Conclude and Apply1. Discuss how the image you see would

change or be different if the surface of thewater were a mirror.

2. Predict how the angles of reflection orrefraction would change if the surface of thecontainer were curved. Explain.

Make a Light Bender

Make a poster of your diagrams and use itto explain reflection and refraction of lightwaves to your class. For more help, refer toyour Science Skill Handbook.

LAB 405Doug Martin

Design Your OwnDesign Your Own


Real-World QuestionPolarizing filters cause light waves to vibrate only in one direction.Wearing polarized sunglasses can help reduce glare while allowingyou to see clearly. If you have two polarizing filters on top of oneanother, when will light shine through and when will it not? Whatmight happen if you added a third filter in between the first two?

Form a HypothesisForm a hypothesis about how two polarizing filters that are placed ontop of one another must be oriented for light to shine through and forno light to shine through.

Test Your HypothesisMake a Plan1. Using a pair of polarizing filters, choose at least three orientations

of the filters to test your hypothesis.

2. When the two filters are oriented to allow the maximum amountof light to shine through, predict how a third filter placed betweenthe two must be oriented for the same results.

Goals■ Demonstrate when

light does and does notshine through a pair ofpolarizing filters.

■ Predict what will hap-pen when you add athird polarizing filter.

Possible Materialspolarizing filters (3)lamp or flashlight

Safety Precautions

WARNING: Never lookdirectly at the Sun, evenwith a polarizing filter.

Polarizing Filters

Dominic Oldershaw

LAB 407

The next time you see a family member orfriend wearing sunglasses, explain to themhow polarizing lenses can reduce problemsof glare.

3. Repeat step 2 but allow no light to shine through.

4. Make sure that your teacher approves your plan beforeyou start.

Follow Your Plan1. Using an appropriate light source, test when light does and

does not shine through a pair of polarizing filters. Test eachof the orientations you planned in step 1. Record the results.

2. Test three orientations of the third filter for allowing the maximum amount oflight to pass through. Record the results.

3. Repeat step 2 but allow no light to shine through. Record the results.

Analyze Your Data1. Describe how the pair of polarizing filters were oriented when light did and did

not shine through. In cases where light did shine through, was it always the sameamount of light? Or did the amount of light change in different orientations?

2. In each case, describe what happened when you added a third filter betweenthe first two. How did the three orientations of the third filter change theamount of light that passed through? Explain.

Conclude and Apply1. Explain why light did or did not shine through two polarizing filters in the vari-

ous orientations.

2. Evaluate why or why not your hypothesis was supported.

3. Infer why light did or did not shine through various orientations of three polar-izing filters.

4. Analyze whether or not your predictions were correct.

5. Discuss what you can conclude about the polarization of reflected light if a polar-izing filter reduces the brightness of light reflected from the surface of a lake.

Dominic Oldershaw

A Haiku Garden:The Four Seasons in Poems and Prints

by Stephen Addiss with Fumiko and Akira Yamamoto

Respond to the Reading1. How do the illustrations help the reader

better understand the poems?2. What do you think is meant by the

word lingering in the Haiku about springsunlight?

3. Linking Science and Writing Writeone haiku about summer and anotherabout fall. In one poem, use color tohelp you describe the season. In theother, use light or some property oflight to help describe the season.

Research has deter-mined that there is a

connection between color and mood. Warmcolors have longer wavelengths, and can bemore stimulating. Cool colors, which haveshorter wavelengths, tend to have a calmingor soothing effect on people. Light and colorhave long been used as literary symbols. Doesthe use of color change what you imaginewhen you read the haiku?

UnderstandingLiteratureJapanese Haiku A haiku is a verse thatconsists of three lines and 17 syllables inthe Japanese language. The first and thirdlines have five syllables each, and themiddle line has seven syllables. Why isimagination important in reading Haiku?


Lingering

in every pool of water—

spring sunlightIssa

Withered by winter

the sound of the wind—

one-color worldBasho

(t)Archivo Iconografico, S.A./CORBIS, (b)Ashmolean Museum, Oxford, UK/Bridgeman Art Library, London/New York

The Behavior of Light

1. When light interacts with matter, somelight can be absorbed, some can be trans-mitted, and some can be reflected.

2. When light waves are reflected, they obeythe law of reflection—the angle of inci-dence equals the angle of reflection.

3. Light waves are refracted, or bent, when alight wave changes speed as it travels fromone material to another.

Light and Color

1. You see color when light is reflected offobjects and into your eyes.

2. Specialized cells in your eyes called conesallow you to distinguish colors and shapesof objects. Other cells, called rods, allowyou to see in dim light.

3. Red, blue, and green are the three primarycolors of light and can be mixed to form allother colors.

4. The color of a pigment is due to the wave-lengths of the light reflected from the pig-ment. The primary pigment colors aremagenta, cyan, and yellow.

Producing Light

1. Incandescent bulbs produce light by heat-ing a tungsten filament until it glowsbrightly.

2. Fluorescent bulbs give off light when ultra-violet radiation produced inside the bulbcauses the phosphor coating inside the bulbto glow.

3. Neon lights contain a gas that glows whenelectric current passes through it.

4. A laser produces coherent light by emitting abeam of light waves that have only one wave-length, have their crests and troughs aligned,and are moving in a single direction.

Using Light

1. Polarized light con-sists of transversewaves that vibratealong only oneplane.

2. Total internal reflec-tion occurs when alight wave strikes theboundary betweentwo materials at anangle greater thanthe critical angle.

3. Optical scannerssense reflected lightand convert theinformation to digital signals.

CHAPTER STUDY GUIDE 409gpscience.com/interactive_tutor

Use the Foldable that you made at the begin-ning of this chapter to help you review light transmission.

(tl)Dick Poe/Visuals Unlimited, (br)Timothy Fuller


Answer the following questions using completesentences.

1. What type of light does heating a filamentuntil it glows produce?

2. What process would you use to produce acomplete three-dimensional image of anobject?

3. How would you describe an object that youcan see through?

4. What process makes it possible for opticalfibers to transmit telephone conversationsover long distances?

5. What is a false image of a distant object?

6. What type of light has light waves thatvibrate in only one direction?

Choose the word or phrase that best answers thequestion.

7. Which word describes materials that absorbor reflect all light?A) translucent C) ultravioletB) opaque D) diffuse

8. What is the term for the property of amaterial that indicates how much lightslows down when traveling in the material? A) pigment C) index of refractionB) filter D) mirage

9. Which of the following explains why aprism separates white light into the colorsof the rainbow?A) interference C) diffractionB) fluorescence D) refraction

10. What do you see when noting the color ofan object?A) the light it reflectsB) the light it absorbsC) polarizationD) diffuse reflection

11. What do the phosphors inside fluorescentbulbs absorb to create a glow?A) incandescent lightB) ultraviolet radiationC) halogensD) argon

12. What term describes objects that allowsome light, but not all light to passthrough them?A) translucent C) transparentB) reflective D) opaque

13. Which light waves are bent most whenpassing through a prism?A) red waves C) blue wavesB) yellow waves D) violet waves

14. Which type of cells in your eyes allows youto see the color violet?A) red cones C) blue conesB) green cones D) rods

15. What color of light is produced when thethree primary colors of light are combinedin equal amounts?A) black C) whiteB) yellow D) cyan

16. Which of the following terms bestdescribes laser light?A) incoherent C) incandescentB) coherent D) fluorescent

410 CHAPTER REVIEW

coherent light p. 398fluorescent light p. 395holography p. 401incandescent light p. 394incoherent light p. 398index of refraction p. 386mirage p. 388

opaque p. 384pigment p. 392polarized light p. 400total internal reflection

p. 402translucent p. 384transparent p. 384

gpscience.com/vocabulary_puzzlemaker


CHAPTER REVIEW 411gpscience.com/chapter_review

17. Concept Map Copy and complete this concept map to show the steps in the production of fluorescent light.

18. Concept Map Copy and complete the follow-ing concept map about producing light.

19. Explain how light is produced by an incan-descent bulb. What is a disadvantage ofthese bulbs?

20. Compare and contrast the reflection of lightfrom a white wall with a rough surfacewith the reflection of light from a mirror.

21. Predict what color a white shirt wouldappear to be if the light reflected from theshirt passed through a red filter and thenthrough a green filter.

22. Identify the color of light that changesspeed the most as it passes through aprism. Explain your reasoning.

23. Infer Most mammals, including dogs andcats, can’t see colors. Infer how the retinaof a cat’s eye might be different from theretina of a human eye.

24. Compare White light passes through atranslucent pane of glass, and shines on ashirt. Both the translucent glass and theshirt appear green. Compare the colors oflight that are absorbed and transmitted bythe glass and the shirt.

25. Explain The speed of light is greater in airthan in glass. Explain whether or notinternal reflection could occur when alight wave traveling in air strikes the glass.

Interpreting Graphics

26. Calculate Angle of Incidence A light ray isreflected from a mirror. If the anglebetween the incident ray and thereflected ray is 136 degrees, what is theangle of incidence?

27. Calculate Speed The index of refractionof a material equals the speed of lightin a vacuum, which is 300,000 km/s,divided by the speed of light in thematerial. What is the speed of light inwater if the index of refraction forwater is 1.33?

Initiating step

Final outcome

by heatedmetals

by glowinggases

used in

by coherentlight waves

used in

ProducingLight


Record your answer on the answer sheetprovided by your teacher or on a sheet of paper.

1. Which word describes materials that trans-mit almost all of the light that strikes them?A. translucent C. opaqueB. transparent D. diffuse

Use the diagram below to answer questions 2 and 3.

2. How are the light waves shown described?A. coherent C. opaqueB. incoherent D. translucent

3. What device produces these light waves?A. fluorescent lightB. sodium-vapor lightC. laserD. incandescent light

4. What happens when light traveling at anangle passes from one material into another?A. The light is reflected.B. The light is refracted.C. The light always speeds up.D. The light changes color.

5. Why does an apple look red?A. It reflects red light.B. It absorbs red light.C. It reflects all colors of light.D. It reflects all colors of light except red.

6. Which of the following processes is used inoptical fibers to transmit light?A. diffuse reflectionB. total internal reflectionC. polarizationD. incandescence

7. What part of the eye enables you see colorin bright light?A. rods C. conesB. retina D. lens

8. What do the phosphors inside a fluores-cent bulb absorb to make the bulb emitvisible light?A. infrared radiationB. ultraviolet radiationC. electronsD. sodium vapor

Use the illustration below to answer questions 9–11.

9. When the primary colors of light are addedtogether, what color appears in area H?A. magenta C. cyanB. yellow D. white

10. What color appears in area G?A. magenta C. cyanB. yellow D. white

11. Which of the following light sources pro-duces light by making a piece of metal hotenough to glow?A. fluorescent light C. neon lightB. incandescent light D. laser light

412 STANDARDIZED TEST PRACTICE

Red F

H

G K

Blue

Green

STANDARDIZED TEST PRACTICE 413

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the illustration below to answer questions 12 and 13.

12. Identify the object shown in the figure andexplain how it affects white light thatpasses through it.

13. Identify the colors that would be seen onthe right side of the object, in order ofdecreasing wavelength.

14. Why would a green leaf appear to be blackwhen you look at the leaf through a redfilter?

15. Describe the effect that diffuse reflectionwould have on a beam of parallel light rays.

16. Describe the difference between an objectthat appears black and an object thatappears white.

17. If green light shines on a black-and-whitestriped shirt, what colors will the stripesappear to be?

18. Why is an electric current needed to pro-duce light in fluorescent lights and inneon lights?

19. For a regular reflection to occur, how mustthe roughness of a surface compare to thewavelengths of light it reflects?

Record your answers on a sheet of paper.

20. Why can the human eye see colors betterin bright light than in dim light?

21. Explain why, compared to the light from alightbulb, a beam of laser light can delivera large amount of energy to a small area.

22. Explain whether or not a large bottlemade of green glass would be a suitablecontainer in which to grow small plants.

Use the illustration below to answer questions 23 and 24.

23. When a light wave traveling in water reachesthe water’s surface, under what circum-stances will total internal reflection occur?

24. If the flashlight were in air and the directionof the light beams shown in the figure werereversed. Under what circumstances wouldtotal internal reflection occur? Explain.

gpscience.com/standardized_test

Whitelight

Red

Air

Normal Normal

Water

Answer All Parts Make sure each part of a question isanswered when listing discussion points. For example, if thequestion asks you to compare and contrast, make sure you listsimilarities and differences

Question 17 Be sure to describe the change in color of boththe black and the white stripes.


Documents

13.1 The Behavior of Light 13.2 Light and Color 13.3 Producing Light 13.4 Using Light That Inner