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  • Color Filters and Light

    delta science modules Color and Light 37


    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


    About 60 minutes




    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


    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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  • 38 activity 4 Color Filters and Light


    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 puretheyallow 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.



    Predictionswill vary.



    Predictionswill vary.

    Activity Sheet 4, Part A

    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

    Predictionswill vary.


    There areover 20possibilities.

    blue-greendark violetgreengreenredgreen

    Activity Sheet 4, Part B

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  • delta science modules Color and Light 39

    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 backorfilters outlarger 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

    Additional Information

    After about 15 minutes, turn on the classroomlights and begin a discussion of the studentsresults. 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



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

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  • delta science modules Color and Light 41

    Additional Information

    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 doesnt 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 combiningr


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