lesson where does color come from? - carolina … · where does color come from? ... investigate...

82 STC/MS™ LI G H T

INTRODUCTIONIn the fall, hundreds of thousands of touristsfrom all over the world go to New England toenjoy the changing colors of the leaves. Color isvery important to them, but then it is importantto everyone. Whether you are shopping for newclothes or a car, following a marked trail in thewoods, or waiting for a red light to turn green,color matters. Color provides you with a greatdeal of useful information about your environ-ment. The universe would certainly be a dullplace without it. So, what is color? Why dothings appear to be colored? Where does colorcome from? When you see color, what exactlyare you seeing? In this lesson and the four thatfollow, you will try to answer some of thesequestions as you investigate color.

8Where Does Color Come From?

LESSON

OBJECTIVES FOR THIS LESSON

Investigate where color comes from.

Discuss the appearance of the visiblespectrum.

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When people enjoy the fall colors,

what are their eyes detecting?

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Getting Started

1. Collect the plastic box of materials. Takeout the flashlight and triangular prism.Wait until you do Inquiry 8.1 to divide therest of the materials between the pairs inyour group.

2. Hold the triangular prism close to youreye and look around the room. Lookthrough the window and at the lights inthe classroom. Make sure your partnergets a turn. Discuss with your partnerwhere you have seen this effect before.

3. After your teacher has darkened the room,shine the flashlight through the prism ontothe ceiling. Try holding the prism at differ-ent distances from the flashlight and turn-ing the prism around in the beam of light.What do you observe?

4. Discuss your observations with your groupand with the class.

MATERIALS FORLESSON 8

For your group1 ray box 1 ray box lid1 60-W clear halogen

lightbulb1 extension cord1 bulb holder2 narrow-slit ray box

masks 2 no-slit ray box

masks

For you and your labpartner1 triangular prism1 flashlight2 D-cell batteries 1 white screen2 plastic stands1 box of colored

pencils


LESSON 8 WH E R E DO E S CO L O R CO M E FR O M?

Inquiry 8.1Using a TriangularPrism To ExamineWhite LightPROCEDURE

1. Record your responses for thisinquiry in your science notebook.There is no student sheet for thislesson.

2. Watch as your teacher demon-strates how to set up the raybox, prism, and white screen.Use Figure 8.1 as a guide as youfollow the instructions to con-struct your ray box set out inthe diagrams labeled a–d.

SAFETY TIP

The lamp in theray box gets hot.Allow it to coolfor at least 5 minutes beforehandling thelightbulb.

Figure 8.1 Assembling the ray box. Two pairs can use each box.

Open the box. Put it on the table. Place the lidon the box. The flaps fit inside. Attach theextension cord to the bulb holder.

Screw the lightbulb into the lid. Screw the bulbholder onto the lightbulb.

a

b



Block off two opposite windows in thebox with no-slit masks.

3. Place the triangular prism in the path ofthe light ray.

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Slot two narrow-slit masks in the remaining win-dows. The bottom of the slit should be as close tothe table as possible.

A. Draw what happens to the path of thelight ray as it enters and leaves the prism.



SAFETY TIP

Turn off the raybox immediatelyafter you finishusing it. Allowthe ray box tocool.

Figure 8.2 Can you get the colors you observed in “Getting Started” to form on

your screen?

4. Attach the plastic stands to the whitescreen. Place the screen in the path of thelight ray leaving the prism. Rotate theprism and, if necessary, move the screen(as shown in Figure 8.2) until you get thesame colors you observed in “GettingStarted.”

B. Use colored pencils to draw what yousee.

C. Write down the names of the colors inthe order in which you observe them.

D. Can you get the colors to appear onthe screen in a different sequence?

5. Where do you think the colors youobserved came from? Discuss your ideaswith your partner. Here are some ques-tions to consider:

What happened to the light rays whenthey first entered the prism?

Did all the colors leave the prism at thesame place?

What did the prism do to the white light?

E. Write a paragraph explaining whereyou think the colors came from.

REFLECTING ON WHAT YOU’VE DONE

1. Scientists once thought that glass addedcolors to white light. What do you thinkof this hypothesis? How could you test it?Discuss this idea with your group. Be pre-pared to engage in a class discussion.

2. Read “The Impurity of White” andrecord your responses to A and B inyour notebook.

A. What did Newton’s experiments prove?

B. Write a paragraph summarizing hisexperiment.

Light ray



For centuries the Western world hadthought of white as the color of purity.The color white was associated with allthat is pure and innocent. Along came ayoung English scientist, Isaac Newton(1642–1727), who changed people’sideas about the world of color forever. Itwas Newton who discovered in the 17thcentury that white light is not pure; it isa mixture of different colors.

Working in a darkened room, Newtonexperimented with a beam of light byallowing sunlight to shine into the roomthrough a small hole in the wall. He then

All color comes from light, whether it is the colored beak

of a spectacular bird like this penguin or the bright col-

ors of clothing. All things that are colored reflect some of

the colors that make up white light.

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The Impurity of White



passed this beam of light through a glassprism. The result was a line of different col-ors, which he projected onto a white screen.But this part of his experiment was not new.

Many people had already observed thatwhite light can produce a line of colors that iscalled a spectrum. For thousands of years,people observed how colors were producedwhen sunlight shone through crystals ordroplets of water.

Everyone recognized these colors were thesame as those found in rainbows. Most peoplebelieved that pure white light from the Sunwas changed or contaminated in some waywhen it passed through the crystals or water.But on that day in 1666, Newton took hisexperiment one step further. And what he dis-covered turned people’s ideas about the worldof color upside down.

Recombining the Spectrum“What would happen,” Newton wondered, “if Iused another prism but turned it upside downwith respect to the first? Then the colors pro-

Newton used prisms and a lens to recombine the colors in white light. Sunlight came in from the left, was split into its

spectrum, and then was recombined using a lens and a second, identical, upside-down prism.

White lightfrom the Sun

White lightrecombined

LensColors of thespectrum

duced by the first prism would shine into thesecond one.” He tried out his idea. He usedtwo prisms and a lens, as shown here.

The first prism produced a colored spec-trum. The lens then focused the spectrumonto a second, identical, upside-down prism.The spectrum left the second prism as a ray ofwhite light. Newton could think of only onelogical explanation. Instead of contaminatingwhite light, the first prism split it into the dif-ferent colors that make up white light. Thesecond prism recombined those colors backinto white light. White was not pure, butinstead a mixture of color.

At the time many people found Newton’sdiscovery very disturbing. It took quite a fewyears before they could accept that white wasnot a pure color. In fact, it was the least pureof all colors. At first, there was much opposi-tion to his discovery. However, Newton’sexperiment was easily repeated. By the end ofthe 17th century, it was widely accepted thatNewton’s explanation of the spectrum pro-duced by white light was the correct one. �



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Newton used a glass prism and a beam of sunlight to produce a spectrum. Where did the colors in this spectrum

come from?



A rainbow is not made from a single prismlike the one you used, but a summer showerdoes contain billions of raindrops. As sunlightenters each drop, it bends, bounces off the backof the raindrop, and bends again when it leaves.As you can see from the illustration, bendingthe sunlight makes the white light split—justlike a prism bends and splits white light. Theraindrops that produce a rainbow behave a bitlike billions of tiny prisms.

White light is made up of the many colors of vis-ible light—light we can see. A prism splits whitelight into these colors. It does this by bendingthe various colors of light at slightly differentangles as they enter the prism. This causes thecolors to spread out, splitting them apart.

You have seen these colors before. They arethe same ones that make up a rainbow. But arainbow does not contain a prism, so how arethe colors of a rainbow made?

Explaining a

Rainbow

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But why does a rainbow look likebig bands of color? Inside each rain-drop, each color of white light isbent a different amount. Because theraindrops are in different positionsin the sky, they bend different colorsto your eye. The appearance of therainbow depends on the raindropsthat make it up. Larger droplets sep-arate the colors well, making thecolors of the rainbow appear moredistinct. When the droplets are verysmall, the colors can overlap andthe rainbow becomes almost whiteand more difficult to see.

Although a rainbow appears to bean arc stretching across the sky, itactually forms a full circle. To anobserver standing on Earth’s surface,the rest of the circle is hidden belowthe horizon. There is no end to arainbow!

Colored bows can be seen wher-ever sunlight strikes water dropletsat certain angles. Many waterfallsproduce rainbows in their spray.Sometimes bows of color (“dewbows”) can be seen on early morn-ing dew. �

A rainbow has many colors. How manyexactly? Some people suggest there areonly seven: red, orange, yellow, green,blue, indigo, and violet. They even have anonsense phrase to help them rememberthem—ROY G BIV. How many colors did youdetect using your prism? Were there onlyseven? Could you see a greenish blue or ayellowish green? In fact, there are millionsof colors in a rainbow. It’s just that wehave names for only a few of them!

Can you see in a rainbow or through aprism all the colors our eyes can perceive?Try looking for magenta or brown.

You don’t need rain to make a rainbow. The spray from a

waterfall can produce its own rainbow.

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White light from Sun

Raindrops

White light from Sun

Your eye

Violet light

Red

light

Raindrops split white light into the colors that make it up. Raindrops

in different positions send different colors to the eye of someone

looking at the rainbow. Red light is seen from raindrops at an angle

of 42 ° to the horizon, violet light from raindrops at an angle of 40 °.

The other colors of the rainbow are seen at angles between 40 ° and

42 °. This is why rainbows are only visible to the observer as a nar-

row curved band in the sky. Using this diagram, think about what

direction—up or down—you would have to look to see red light or

violet light.

Which Colors Are in a Rainbow?

lesson where does color come from? - carolina … · where does color come from? ... investigate...

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