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Color Filters and Light

delta science modules Color and Light 37

activity

Color Filters and LightOBJECTIVES

Students add to their understanding ofsubtractive color mixing by investigating theeffect of filters on the color of light.

The students

� shine white light through color filters andobserve how the color of the light changes

� predict and then observe the effects ofpassing white light through differentcombinations of color filters

� compare this process with the process ofmixing pigments

SCHEDULE

About 60 minutes

VOCABULARY

filter

MATERIALS

For each student

1 Activity Sheet 4, Parts A and B

For each team of two

2 batteries, D-cell

1 flashlight

1 sht paper, white

For the class

3 shts acetate, blue

1 sht acetate, frosted

3 shts acetate, green

4 shts acetate, orange

3 shts acetate, red

4 shts acetate, violet

3 shts acetate, yellow

6 bags, plastic, reclosable

1 pair scissors*

1 roll tape, masking

*provided by the teacher

PREPARATION

Make a copy of Activity Sheet 4, Parts Aand B, for each student.

Install batteries into flashlights, and checkto see that all of the flashlights workproperly.

Cut the sheet of frosted acetate intosquares 5 cm × 5 cm (about 2 in. × 2 in.),one square per flashlight. Tape a frostedacetate square over the working end ofeach flashlight so that the lamp iscompletely covered by the square. Makesure that the tape does not obstruct any ofthe light.

Cut the sheets of blue, green, orange, red,violet, and yellow acetate into pieces 10cm × 12.5 cm (about 4 in. × 5 in.). Thesepieces of acetate will now be referred to ascolor filters. Note that you will probablynot use all of the pieces that you cut inthis activity. Return all extra pieces to thekit.

Each team of two will need a workingflashlight with a piece of frosted acetatetaped over one end, a sheet of whitepaper, and six color filters (one each ofblue, green, orange, red, violet, andyellow).

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© Delta Education LLC. All rights reserved.

38 activity 4 Color Filters and Light

BACKGROUND INFORMATION

A filter is a substance or device thatprevents certain things from passingthrough it while allowing certain otherthings to pass. Color filters allow onlycertain colors of light to pass through themby absorbing all the rest. When white lightshines on a red filter, for example, theorange, yellow, green, blue, and violetcomponents of the light are absorbed by thefilter, allowing only the red component ofthe light to pass through to the other side ofthe filter.

A pure filter allows only a single color oflight to pass through it. Like pigments,however, most filters are not pure—theyallow more than one color through. Forexample, most yellow filters also allowsome red, orange, and green light to passthrough them, but our eyes see a mixture ofyellow, red, and green light as simplyyellow. Likewise, a blue filter allows someviolet and green as well as blue light topass, but our eyes perceive the mixture asblue.

Overlapping different color filters (placingone on top or in front of another) is a lot likemixing different food colorings in that newcolors are formed by the process ofsubtractive color mixing. Each color filterthat is added subtracts certain colors fromthe colors of light that strike it. For example,if the blue and yellow filters mentionedabove were overlapped, the yellow filterwould absorb the blue and violet light thatpassed through the blue filter, allowing onlythe green through.

The frosted acetate is used in this activity todiffuse the light from the flashlight, makingthe light intensity more uniform.

Color Filters and Light1. Fold the sheet of white paper in half so that it stands up by itself in the shape

of an upside-down V. You will use this as a screen to shine light on.

2. Choose a color filter and predict what you will see when you shine lightthrough it. Record your prediction in the chart. Then place the filter in front ofthe flashlight and shine the light on the screen. Record your results. Repeat forthe remaining five filters.

3. Use two filters for this step. For each combination of filters, predict what colorlight you will see. Record your prediction. Then place both filters in front of theflashlight and shine the light on the screen. Record your results.

Filter Color Prediction Results

Filter Color Prediction Resultsred + yellowyellow + blue

blue + redgreen + redblue + greengreen + yellow

There are over 15possibilities.

red-orange

greenvioletgreenturquoisegreen

Predictionswill vary.

redorangeyellowgreenblueviolet

redorangeyellowgreenblueviolet


Activity Sheet 4, Part A

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Color Filters and Light4. Use three filters for this step. For each combination of filters, predict what

color light you will see. Record your prediction. Then place the three filters infront of the flashlight and shine the light on the screen. Record your results.

Filter Color Prediction Results


g+b+yr+v+bg+v+br+b+gr+b+yo+b+g

There areover 20possibilities.

blue-greendark violetgreengreenredgreen

Activity Sheet 4, Part B�



Additional Information

Write the word filter on the board. Ask thestudents, What do you think a filter is? Canyou give an example?

Tell the students that in this activity they willobserve what happens when white lightpasses through color filters.

Hold up several of the color filters. Ask, Whatdo you think these objects filter out or allowthrough?

What does the red filter block and whatdoes it let through?

Divide the class into teams of two. Distributea copy of Activity Sheet 4, Parts A and B, toeach student. Go over the instructions on theactivity sheets with the students.

Distribute a sheet of white paper, a flashlightwith a piece of frosted acetate taped to it, anda set of filters (blue, green, orange, red,violet, and yellow) to each team of students.

Demonstrate how to position the flashlightand filters and how to fold the sheet of whitepaper in half so that it can set up as a paperscreen (see Figure 4-1).

Tell students to predict what will happenwhen the white light from their flashlightsshines through each individual color filter.Have them record their predictions on theactivity sheets.

Darken the room. Allow about 15 minutes forthe students to experiment with each of thesix filters and to complete the chart at the topof their activity sheets.

A filter is something that lets certain thingsthrough but blocks others. An example is awire mesh sieve that allows sand andpebbles to fall through, but holds back—orfilters out—larger stones. Another example isa kitchen strainer used to drain the waterfrom spaghetti or vegetables.

Each one filters out certain colors of light andallows other colors to pass through.

It lets red light through but blocks (absorbs)other colors of light. Some students mayknow or guess that it actually lets throughsome other colors in addition to red (such asorange and violet).

Tell students that only single filters should beused at this point; combinations of filters willbe tested shortly.

Guiding the ActivityGuiding the Activity

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40 activity 4 Color Filters and Light


After about 15 minutes, turn on the classroomlights and begin a discussion of the students’results. Ask, What happened when youshined white light from the flashlightthrough a blue filter? Why? What happenedto the other colors that make up the whitelight?

Ask, What do you predict will happen whenyou shine your flashlight through twooverlapping color filters?

Remind students to record their predictions inthe second chart on their activity sheets.

Darken the room again. Allow about 15minutes for the students to experiment withcombinations of two overlapped filters. Tellthem to record their results on their activitysheets.

The light that passed through the blue filterwas blue because all the other colors werefiltered out, or absorbed, by the blue filter.

Answers may vary.

Guiding the Activity

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� Figure 4-1. Which colors of light will pass through the filters?




After about 15 minutes, turn on the classroomlights and ask, What happened to the lightwhen you overlapped two filters? Does thelight change color when you add filters?Does it get brighter or dimmer? Why?

Ask, What do you predict will happen if youshine light though three overlapping colorfilters?

Have students record their predictions in thethird chart on their activity sheets.

Darken the room once again so the studentscan test their three-filter combinations.Remind them to record their results.

When students have finished testing theirthree-filter combinations, instruct them tooverlap all six filters at one time and toobserve what happens to the light.

Ask, Why doesn’t any light get through tothe screen?

Turn on the classroom lights. Ask, Do theresults you obtained overlapping filtersremind you of anything else you haveexamined recently?

Ask, Did you notice any differences betweenthe results obtained using overlappingfilters and the results obtained by mixingcolored water? How would you explainthese differences?

One remarkable difference is that combiningred and yellow filters results in essentially redlight, not the expected orange. This isbecause a yellow filter can allow a largeamount of red and green light to pass throughit and still look yellow, whereas the red filteris much more effective at blocking out othercolors. Similarly, overlapping green andyellow filters yields a much darker green thanstudents might expect after their pigment-mixing experiments.

The light changes color because each addedfilter absorbs additional colors of light. Theintensity of the light decreases (the light getsdimmer) because each color removeddiminishes the total amount of light that getsthrough the filters and hits the paper screen.

No light is able to pass through all six filters.

Every color of light in the spectrum has beenabsorbed by one or more of the color filters.

The students should recognize thatoverlapping the filters formed new colors in amanner similar to what they observed whenmixing water colored with pigments.

Students may come up with a variety ofresponses.

Guiding the ActivityGuiding the Activity

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REINFORCEMENT

Prepare three glasses of water: To one, add10 drops of red food coloring; to a second,add 10 drops of blue food coloring; and to athird, add 10 drops of yellow food coloring.Show students that colored water acts like afilter, changing the color of the light thatpasses through it. Have students experimentto see whether overlapping colored liquidsyields the same results as overlapping filters.Then challenge them to find ways in whichthe two processes differ and to explain why.For example, overlapping glasses of red andyellow colored water results in very orangelight, while overlapping red and yellow filtersresults in very red light. This is because redfood coloring allows more orange light topass through than the red filters do.

Assessment Opportunity

This Reinforcement also may be used as an ongoing assessment of students’understanding of science concepts and skills.

SCIENCE JOURNALS

Have students place their completedactivity sheets in their science journals.

CLEANUP

Leave the squares of frosted acetate tapedto the flashlights for use in Activity 5. Placethe color filters into the plastic, reclosablebags, one color per bag. Return theflashlights, paper screens, color filters, androll of masking tape to the kit.

42 activity 4 Color Filters and Light© Delta Education LLC. All rights reserved.


Connections

Science ChallengeAsk students to find out what the wordstransparent, translucent, and opaque meanand to give examples of materials that can bedescribed in these terms. (Transparentmaterials allow light to pass directly throughthem; objects can be seen clearly throughtransparent materials. Translucent materialsallow light to pass through them but scatter itin all directions; objects cannot be seenclearly through translucent materials. Opaquematerials do not allow any light to passthrough them; objects cannot be seen at allthrough opaque materials.)

Science ExtensionPose the following question to the class: Ifsunlight is white light, and air has no color,why does the sky look blue during the dayand red, orange, or pink at sunrise andsunset? Give students some time to thinkabout and discuss the question, then havethem do the following activity in teams. Fill adrinking glass or other tall, clear containerwith water. Hold a sheet of white paperbehind the container, and shine a flashlightdirectly at the container from the other side.Students will see white light shining on thepaper. Next have students add about half ateaspoon of milk to the water, mix itthoroughly, and then shine the flashlight at itfrom the side again. This time, the cloudywater in the container and the light shining onthe paper will be reddish orange. Also havestudents shine the light down into thecontainer from above and note the bluish-greycolor of the cloudy water. Repeat your originalquestion, and ask students to use theirobservations to try to answer it, at leastpartly. (Air in the atmosphere contains billionsof tiny dust particles. When sunlight hitsthese particles, it bounces off them andscatters. Blue and violet light waves scatterthe most, orange and red waves the least.When the sun is higher in the sky during theday, less light is scattered and more blue light

reaches our eyes, making the sky appearblue. When the sun is low in the sky at sunriseor sunset, most of the blue light is scatteredand primarily red and orange light color thesky. This phenomenon also explains whyspectacular sunsets often occur after avolcanic eruption releases ash and dust intothe atmosphere.)

Science and the ArtsSuggest that students find out how stainedglass windows are made for churches, homes,and public buildings. Students might enjoymaking a model of a stained glass window bycutting out sections of a sheet of black oaktag, leaving areas between the cut-outsections to represent the leading that holds astained glass window together, then gluingpieces of tissue paper over the cut-outsections and coloring them with markingpens. Have students hang their completedwindows against the classroom window sothey can observe the amounts and colors oflight that pass through the sections.

Science, Technology, and SocietyAsk students whether they have ever seen astore window covered with a transparent,yellow window shade. Ask them why suchshades are used. (to keep materials in thedisplay from being faded and discolored bysunlight) Explain that the shades act as filtersto screen out some of the sun’s rays but stillallow people to view the display withoutdistorting its colors too much. Let studentstest the fading power of sunlight by hanging abrightly colored strip of fabric in a sunnyplace, putting an identical strip in a darkplace, and comparing the color of the stripsevery week for a month or two.


Download - Color Filters and Light Color Filters and Light

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