Introduction, Workshop Outline, Materials List, and Bibliography

This unit divides color and color vision into four major topics:

• The eye and color vision; colors from mixing light or pigments

• The colors of surfaces and light sources; absorption and emission, refraction, scattering, and diffraction and interference

• Colors from interference involving diffraction and thin films

• Colors from interference involving polarization

The letters used in the list above are used throughout, but the unit is also divided into the sections listed below. To make it easier to draw on the materials in the different sections when dealing with a particular topic, the pages are numbered with “section”, “topic”, “page number.” For example, the modern physics application dealing with optically active materials and liquid crystals begins on page 9D-1, since it involves polarization. The letters are omitted for items which are general to the whole unit.

The sections are in the following order:

1. Introduction, Table of Contents, and Bibliography

2. Background Material for Teachers, and Transparency Masters

3. Laboratory Activities

4. Demonstrations and Displays

5. Assignments and Homework

6. Computer Applications

7. Use of Technology

8. Physics Olympics or Contest Events

9. Modern Physics Ideas or Contemporary Uses

10. Test questions or Other Assessment Techniques

We expect that teachers will present some or all of the laboratory activities in section 3, and will provide explanations interspersed between them. Section 2 has suitable explanations written out. While section 2 could be used for independent study by a few exceptional students, it is intended to be used by the teacher in preparation for teaching the unit. A ClarisWorks™ document, described on page 2D-9, provides a way to customize the graphs used in section 2D to a particular tape.

Cindy Miller contributed greatly to the sections on color vision and color mixing, and provided many of the supplementary materials. Judy Franklin contributed a song and some organizational strategies, as well as proofreading and assembly of the materials. The rest of the unit was written by Bill Franklin. Richard Bartels read many versions of the text, and eliminated many errors. Other helpful criticism was provided by Robert Beck Clark; Jim Nelson; Jane Bray Nelson; Jane Rich; the staff and participants of the Physics Teacher Enhancement Program at Texas A&M University, who piloted a trial version of topics C and D; and my students.

We would also like to thank the Polaroid Corporation for the generous donation of the Polaroid™ sheets needed for the PTRA-PLUS workshop at Notre Dame, Paul Chagnon and others at Notre Dame who provided facilities and other support, Robert Greenler and Jane Bray Nelson, who were most generous in providing materials about color mixing, and Robert Bauman and George Burman, who gave us permission to reproduce their articles in this unit.

We hope that you and your students will enjoy learning about color. We have found the beauty of color to be highly motivating to our own students.

Distribute and collect registration forms. During this time, describe the unit and its page numbering system. Refer participants to page 1-2 for particulars.

Have participants mix light if you have suitable sources; otherwise, demonstrate. Have a TV screen available for inspection. Offer “Waste not Thy Hour!” as a filler for those who finish early. A signal of completion, such as an overturned, brightly colored plate, is useful also.

Check to make sure that the participants can all identify the additive and subtractive primary colors, and that they know which additive primaries must be combined to produce each subtractive primary.

Demonstrate color shadows by blocking one or more of the primaries which are overlapping to make white. Ideally, set up three floodlights with red, green and blue filters, and let the participants make their own shadows.

Have participants overlap filters. Have color test patches and color separation overlays available. Also provide a copy of, Light and Vision, a Life Science Library book, or some other source of color vision test materials.

Check to make sure that the participants can identify the additive primary subtracted by each subtractive primary, and that they know how the additive primaries can be obtained by combining the subtractive primaries.

Demonstrate the absorption regions of color filters using a slit and diffraction grating on the overhead projector (See 4A-1). Include yellow or orange fluorescent plastic articles such as rulers or triangles. Also interesting is an anti-spectrum, obtained by using a dark “slit” on a clear background. See 4A-2 for a graphical demo.

Have participants view surfaces with various sources. Have at least one station with a ultra violet source and fluorescent materials.

Check for understanding of the colors seen.

Demonstrate that the slides are both black and white. Superimpose them carefully. A red filter over the “red” one apparently should still only give red, pink, white, and black. With some adjustment of intensity, you should be able to see other colors. Relate this to the color constancy that we are able to maintain under illumination by various sources. Make the point that the eye and the brain do a great deal of processing of visual information to obtain a view of the world.

Another good activity at this point would be a color reversal obtained by viewing an image projected by the overhead projector, then quickly removing the transparency and staring at the white screen. See 4A-4 for a graphical demonstration.

Sing “Sweet Colors by Mixing” (page 2A-6).

Distribute mounted diffraction gratings for viewing the spectra of the various sources. It may be more practical to provide one source at each station and let the groups rotate, or even to set the sources up at the front for viewing by all.

Demonstrate the way a low pressure sodium source reduces colors to pretty much black and white (or pale yellow).

Check for understanding of the mechanisms by which light is emitted.

Have the participants trace rays and check the location of the red and blue ends of the spectra. If facilities permit, you might have them view rainbows in a fine spray of water. A dark background will be helpful.

Check to see that participants understand how their diagrams are related to that at the end of the activity. Emphasize that every droplet is producing the whole spectrum, but that your eye sees one color from any one droplet.

Demonstrate (or have participants do it) the blueness of the scattered light and the orangeness of the transmitted light. Some participants may recall that the the shadow of wood smoke is orangish, while the smoke itself appears bluish.

Using diagrams, explain how a diffraction grating works, and derive the formula for it. (See section 2 B.)

Have the participants measure the specified colors and compare the results obtained in each group. Begin describing colors in terms of wavelengths in nanometers.

Explain how a CD can act like a diffraction grating. (See section 2C.)

Have participants perform both activities. If you have enough lasers, let each group do C1, but a single setup for C2 may be adequate. Groups can use the single setup as they finish C1.

Compare the results. The row spacing of the CD is about 1.6 microns (0.0016 mm).

Explain thin film interference. (See section 2C.)

Distribute the materials and check to be sure that the participants are seeing what is intended.

Provide other examples of thin film phenomena such as sea shells or oil films for participants to view as they finish the activity.

Using the diagrams in section 2C, explain why the colors are pale near the bottom when the film is first formed, and why there are white and non-reflective bands at the top.

Explain how thin films can be used to enhance transmission or reflection.

Provide examples of lens and mirror coatings for the activity.

Demonstrate a dichroic filter.

Show participants how to assemble their own dichroic filters, and allow them to do so. Make sure that everyone checks to see that the transmission and reflection colors are complementary.

Demonstrate polarization with a mechanical model, if necessary.

Allow participants to perform the activity. If conditions are favorable, allow them to view blue sky.

Check to see that all found the correct orientation of the permitted direction.

Have participants perform the activity.

Demonstrate how a component can get through using a mechanical model. (See 4D.)

Check to see that the participants understand how the effect can be understood in terms of vector components.

After the participants have viewed mica, help them get one layer of tape on the slide and viewed properly through the polarizers.

When they have filled out the chart and graph for one layer, use the 3-D model of waves in tape to explain why the colors show up.

Have participants continue adding layers and filling out the charts and graphs.

Use the graphs in section 2D to help participants understand the particular colors they obtained. It is helpful to use a slit and diffraction grating on the overhead projector to show the absorption bands in the spectrum of transmitted light.

While the participants are exploring overlapping slides, distribute slide mounts. Show how the polarizers are placed in and in front of the projector, and how the colors change in a sample slide.

Encourage every participant to make at least one slide and label it with his or her name. Place slides in tray and tell each person what number to look for.

Add music and stir.

Have participants fill out the evaluation form. As participants leave, collect evaluations and discuss “Fair Use Policy’’ as stated inside front cover.

Items you might store especially for this unit are marked with □.

Other items are marked with ◯.

• ◯

  Three light sources There are commercial light boxes designed to facilitate color mixing, but you can also use overhead or slide projectors, floodlamps, or even flashlights. One source can be used if the beams are overlapped with three mirrors.

• ◯

  A TV, laser disk player, and a test pattern such as that on the AAPT Cinema Classics disk or a color computer monitor

• □

  Filters to convert them to red, green, and blue sources (Dick Bartels recommends Roscolene #819 (red), #866 (blue) and #874 (green). Dick Heckathorn recommends Lee #106 red, #119 (blue), and #139 (green).)

• □

  A magnifying glass

• ◯

  An overhead projector

• □

  Cyan, magenta, and yellow gelatin filters (Dick Bartels recommends Roscolene #806 (yellow), #828 (magenta), and #877 (cyan). Dick Heckathorn recommends Lee #104 (yellow), #116 (cyan), and #128 (magenta).)

• □

  Color test patches along the edges of pages with color printing in the newspapers.

• □

  Color transparency sets that newspapers have used, until very recently, to separate the colors for the color printing plates.

• □

  Light and Vision, a Life Science Library book, published by Time Incorporated.

• □

  Slit and diffraction grating to show absorption. An anti-slit (a dark bar across the empty overhead stage) is also interesting. It produces an anti-spectrum.

• □

  Orange and/or yellow fluorescent transparent plastic articles (rulers or triangles)

• ◯

  A white light source, small ones for students or an overhead for the class

• ◯

  A ultra violet light source

• □

  Filters of the additive and subtractive primary colors.

• □

  Small squares of paper in additive and subtractive primary colors, black, others. Include fluorescent articles.

• ◯

  Two slide projectors

• □

  Two B&W slides of a scene taken through red and green (or cyan) filters

• □

  The original scene or a color picture of it

• □

  Neutral density filters or an iris to adjust the intensities of the projectors

• ◯

  An incandescent unfrosted light bulb and variable power source (12 V or 120 V)

• ◯

  Gas discharge tubes: neon, mercury, argon, (others if available) and a power source. If these are unavailable, you can use a neon night light or test light.

• ◯

  A single standard fluorescent lamp tube and fixture

• ◯

  A low pressure sodium lamp, if available

• □

  “Compact fluorescent” lamps and fixtures

• □

  Light emitting diodes of various colors and a suitable low-voltage power source

• □

  Luminescent panels (night light and/or wrist watch). Limelite™ night lights are available in my area at Home Depot for less than $6. The manufacturer is Austin Innovations, Inc., P.O. Box 202530, Austin, TX 78720.

• □

  Diffraction gratings mounted on a card (Project Star Holographic Diffraction Grating (6 ft x 6 in for $36.00), Item #PS-08B, or 2 x 2 slides (10 for $30.00), Item# PS-09, Learning Technologies, Inc., 50 Walden Street, Cambridge, MA 02140, (617) 547-7721)

• ◯

  Ray boxes capable of producing a narrow beam (ray) of white light

• □

  Transparent objects, rectangular or triangular, and circular. The rectangular or triangular objects can be made of solid glass or plastic, or they can be thin walled tanks filled with water. The circular object should be a hollow cylinder filled with water. A transparent 35 mm film canister works well. Small glass jars or beakers will work also, but, if the bottom edge is too rounded, you may have to raise the beam level above the bottom. A plywood panel with a hole the size of the beaker can accomplish this.

• ◯

  A slide or overhead projector is ideal, but a flashlight will do.

• □

  A large beaker or small aquarium filled with water

• □

  Powdered milk (Robert Greenler recommends Sanalac™ non-fat.)

• □

  A mask to cover the overhead stage except for a circular hole the size of the beaker

• □

  A straight filament display lamp and socket

• □

  Two meter sticks

• □

  Diffraction gratings, marked with the number of lines per cm.

• ◯

  A laser

• □

  A compact disc that you don’t care about

• □

  A blob of clay to hold it

• □

  Make a white screen by paper-clipping a sheet of paper to a vertical sheet of cardboard. Folds at each end of the cardboard keep it perpendicular to the table top.

• □

  A compact disc

• □

  A bare-filament incandescent light bulb at ceiling level

• □

  A plate which is half white and half black. For small quantities, you can mask one half of the plate and spray paint the other half black. For larger quantities, you may find it faster to fill a narrow container (I used an ice cube bin.) with black paint, dip the plates halfway, and hang them on a line to dry.

• □

  A square rim about 6 cm on an edge (One 1 cm slice of 6 cm x 6 cm PVC downspout)

• □

  Soda straws

• □

  Soap solution. To make soap solution, mix 100 ml (1/3 cup) Dawn™ dishwashing detergent and 10 ml (2 teaspoons) glycerine in 2 liters of distilled or deionized water. Stir and allow to stand overnight before use. Two liters of soap solution will supply about 75 lab groups.

• □

  A transparent cake cover. These can be obtained from the bakery department of a cooperative grocery store, or you can eat a lot of cake.

• □

  A good lens with anti-reflection coatings on it

• □

  An uncoated lens for contrast

• □

  A projection bulb with a thin film interference reflector. Ask the A-V person at your school to save them for you.

• □

  A dichroic filter (available through Edmund Scientific for about $13 to $21 each).

• □

  Other examples of grating or thin film interference, such as seashells, bird feathers, insect wings, opal, iridescent wrapping paper, diffraction grating ribbon, Newton’s Rings demonstrator (Two clean sheets of plate glass will do), integrated circuit chips with a pattern spacing close enough to act as a diffraction grating

• □

  Iridescent gift wrap, available at department stores or party stores

• □

  A slide mount

• □

  A glue stick and scissors

• □

  Two rectangles of Polaroid™ filter approximately 6 × 7 cm. The material can be purchased in 20” × 50” sheets from Polaroid Corporation, Polarizer Division, 1 Upland Road, NOR-2 lK, Norwood, MA 02062, (800) 225-2770. ($120.00)

• □

  A third polarizer approximately 4 x 5 cm.

• □

  A crystal of Iceland Spar large enough to show double refraction. Available from science catalogs, but probably cheaper from a local rock shop.

• □

  A rubber cord or tubing several meters long, four support poles, two bars about 0.5 m long, three clamps to hold the bars and the end of the cord, one of which must be capable of holding a bar at arbitrary angles to the horizontal, and three sliders. The sliders are made from two pieces of metal or plastic tubing a few cm long glued or soldered at right angles at their centers. For details, see the article by Robert Bauman, which is reprinted in section 4 of this unit.

• ◯

  An overhead projector

• □

  A thin piece of mica. A transistor insulator can be purchased for a few cents at electronics parts stores or you can get Muscovite from rock shops.

• □

  A clear plastic article, such as a picnic fork

• □

  Highland™ 3710 package tape, currently $0.99 at Office Depot.

• □

  A microscope slide

• □

  3-D model of waves traveling through a birefringent material. A 15 to 20 cm length of 0.025” music wire stiffens the model, which is made of card stock.

• □

  A clothespin to clamp the microscope slide

• □

  A white surface (or a mirror reflecting a diffuse light source)

• □

  Scissors

• □

  Diffraction grating 7 × 7 cm, mounted for use on overhead projector

• ◯

  A slide projector

• ◯

  A boom box capable of playing music loudly.

• □

  A slide mount

• □

  Scissors

• □

  Some music with a strong beat

• □

  A motor that turns at about one revolution per second (I’ve been using an old 78 rpm turntable motor) If you can’t find a suitable motor, you could mount the polarizer on the shaft of a cheap motor or some other axle and turn it by hand. But keep it slow--only about one revolution per second.

• □

  One polarizer about 7 × 7 cm with its permitted directions at 45° to the vertical and horizontal

• □

  A second polarizer, a circle at least 15 cm in diameter

Fabulous rewards await you as you complete these tasks. Use your imagination and discover that reading physics assignments can be phun!

Imagine that you are floating in a blue lagoon in Tahiti with the companion of your choice. Decide where you will have dinner.

You have acquired a severe case of sunburn and must remain indoors for several days. To help pass the time, do the following:

YOUR REWARD: You have just won $10,000,000 in the Reader’s Digest Sweepstakes! Plan your life as a millionaire.

Ooops! You need to escape from your greedy relatives. Rent a room in an obscure motel and do the following:

YOUR REWARD: Your students have challenged you to walk on hot coals during the school talent show to demonstrate the Leidenfrost effect. Your confidence in the laws of physics leads you to accept the challenge without fear.

You were overconfident. While your burns are healing, do the following:

YOUR REWARD: As a gesture of appreciation for your excellent teaching, your school district has given you an all-expense-paid trip to Europe for a month beginning the day after Labor Day. Plan your itinerary.

An airline strike in Paris forces you to remain longer than planned. Use your extra time to do the following:

YOUR REWARD: Your school district has offered to completely fund your attendance at the winter meeting of the AAPT. Decide what workshops and sessions you will attend.

The worst blizzard in history has grounded all planes. You are forced to spend the week in the school gymnasium which has been converted into a shelter for students and teachers who could not leave the school. While it’s still daylight, do the following:

YOUR REWARD: The parent of one of your students has offered to donate a classroom set of computers with interfacing boxes because of your exemplary work with his offspring. Design the room to accommodate the computers.

Unfortunately, daddy’s pride and joy flunked your course, and the offer was withdrawn. While you’re waiting to explain this to your principal, do the following:

Your enlightened superintendent has offered to exchange jobs and salaries with you in order to get in touch with students again. Plan how you would run the district.

After three days on your schedule and without explanation, the superintendent abruptly ended the experiment. You are placed back in your classroom at your former salary. After picking up the paper airplanes and repairing the broken furniture, do the following task:

YOUR REWARD: You can share what you learned here with others. We hope you’ll enjoy doing that.

• Central Science Co. (CENCO)

  11222 Melrose Avenue

  Franklin Park, IL 60131

• Delta Education, Inc.

  P.O. Box 950

  Hudson, NH 03051

  1-800-442-5444

• Edmund Scientific Company

  (Specialty Optics)

  101 E. Gloucester Pike Barrington, NJ 08007-1380

  1-609-573-6250 FAX (609)573-6295

• Frey Scientific Co.

  P.O. Box 8101, 905 Hickory Lane

  Mansfield, OH 44901-8101

  1-800-25-FREY

• Hubbard

  P.O. Box 104

  Northbrook, IL 60065

  1-800-323-8368

• LaPine Scientific Company

  6001 S. Knox Ave.

  Chicago, IL 60629

• NASCO

  901 Janesville Avenue

  Fort Atkinson, WI 53538

  1-800-558-9595

• PASCO Scientific

  10101 Foothills Blvd.

  Roseville, CA 9567-9850

  (800)772-8700

• Sargent-Welch Scientific Company

  7300 N. Linder Avenue

  Skokie, IL 60077

  1-800-323-4341

• Creative Publications

  5005 West 110th Street

  Oak Lawn, IL 60453

  1-800-624-0822

• Dick Blick Art Materials

  P.O. Box 1267

  Galesburg, IL 61401

  1-800-447-8792

• Flinn Scientific, Inc. (chemical catalog)

  P.O. Box 219

  131 Flinn Street

  Batavia, IL 60510-9906

  1-708-879-6900

• Friends of Fermilab

  P.O. Box 500, M.S. 777

  Batavia, IL 60510

• Kelvin Electronics

  10 Hub Drive

  Melville, NY 11747

  (800)535-8469 FAX (800)756-1025

• McKilligan Supply Corporation

  435 Main Street

  Johnson City, NY 13790

• Oriental Trading Company, Inc.

  P.O. Box 3407

  Omaha, NE 68103

• Polaroid Corp.

  Polarizer Division

  1 Upland Road, NOR-21k

  Norwood, MA 02062

  (800)225-2770 FAX (617)446-4600

• Schoolmasters Science

  745 State Circle, Box 1941

  Ann Arbor, Michigan 48106

  1-800-521-2832

• Science Kit and Boreal Labs

  777 E. Park Drive

  Tonawanda, NY 14150

• S&S Arts and Crafts

  Colchester, CT 06415

  1-800-243-9232

• Vernier Software

  2920 S.W. 89th Street

  Portland, OR 97225

  (503)297-5317 FAX (503) 297-1760

• Scienceware

  Grau-Hall Scientific

  6501 Elva Avenue

  Sacramento, CA 95819

  1-800-331-4728

• Teachers’ Laboratory Inc.

  P.O. Box 6480

  Brattleboro, Vermont 05302-8480

  1-800-254-3457

• U. S. Toy Co., Inc.

  1227 E. 119th Street

  Grandview, MO 64030

The following groups have publications divisions for teacher reference materials.

American Association of Physics Teachers

One Physics Ellipse

College Park, MD 20740-3845

(301) 209-3300 FAX 301-209-0845

National Science Teachers Association

1840 Wilson Blvd.

Arlington, VA 22201-3000

(703) 243-7100

Optical Society of America

2010 Massachusetts Avenue, NW

Washington DC 20036