Lesson Plan #: AELP-PHS0207
Submitted by: Stacy Griffith
Email: smgriffi@indiana.edu
School/University/Affiliation: Indiana University School of Education
Endorsed by: Deborah Hanuscin
             Indiana University
Date: December 9, 2002

Grade Level: 3, 4

Subject(s):

• Science/Physics
• Arts/Process Skills

Duration: Two 30-45 minute sessions

Description: The purpose of this lesson is to introduce students to the additive and subtractive primary colors and to correct the misconception that red, yellow, and blue are the primary colors.

Goals: Indiana Academic Standards : (Science: Grade 3)
Standard 1: The Nature of Science and Technology

• The Scientific View of the World
  • 3.1.1 – Recognize and explain that when a scientific investigation is repeated, a similar result is expected.
• Scientific Inquiry
  • 3.1.2 Participate in different types of guided scientific investigations, such as observing objects and events and collecting specimens for analysis.
  • 3.1.3 Keep and report records of investigations and observations using tools such as journals, charts, graphs, and computers.
  • 3.1.4 Discuss the results of investigations and consider the explanations of others.
• The Scientific Enterprise
  • 3.1.5 Demonstrate the ability to work cooperatively while respecting the ideas of others and communicating one’s own conclusions about findings.

Objectives:

Materials:

• slide projector
• white screen
• prism
• 6 flashlights with batteries: (can be bought at Wal-Mart, Target, or other department stores)
• scissors
• pencils
• colored filters (red, blue, green, cyan, magenta, and yellow — can be ordered from Edmund Scientifics Company – Tel: 800-728-6999)
• Worksheet and Answer Key

Worksheet and Answer Key in .pdf format; requires free Adobe Acrobat Reader.

Click the icon to obtain the free Reader.

Vocabulary:

Procedure:

Teacher Preparation:
Each group of students should have 6 flashlights and 6 colored filters (red, green, blue, magenta, cyan, and yellow). Depending on the level of students, each group of students should cut out circles that will cover the flashlight’s light with each different colored filter. The flashlights can be taken apart, and the clear plastic cover traced. The filter should be placed on top of the clear plastic cover when then flashlight is put together. (Teachers may choose to do this ahead of time, especially if they do not have the financial capability to have enough supplies for several groups.) Each group will also need a space in the room with a large white piece of paper hung on which they can shine the flashlights.

Teacher Background:
Ask the students what they know about the primary colors. Students may believe that red, yellow, and blue are the primary colors because when they mix blue and yellow paint they get green. While we know that this process works and is used in art classes, it is not scientifically accurate. If these were truly primary colors, we would not be able to create them by mixing other colors; however, if we mix red and green light, the resulting color is yellow. Similarly, if we mix magenta and yellow light, the resulting color is red. Clearly there’s more to it than this! The additive primaries, or the primary colors of light, are red, blue and green. These combine to form white light. If we subtract each of these colors, one at a time, from the white light, we end up with the subtractive primary colors, or the primary pigments—cyan, magenta, and yellow:

• red light + green light + blue light = white light
• white light – red light = cyan light
• white light – green light = magenta light
• white light – blue light = yellow light

In this activity, students will explore the additive and subtractive primaries using colored lights. It is important that teachers do not simplify the names of the colors, calling cyan blue or magenta purple—scientifically, in terms of the spectrum of visible light, cyan and blue are two very different colors, as are magenta and purple. Teacher-guided Exploration:
Place a slide projector in front of a white screen. Turn on the projector. Position a prism in front of the light. Place the screen at a shallow angle intercepting the light, so that the rainbow is spread over a greater distance. This makes it easy to see the colors. When light travels through the triangular-shaped piece of glass, the light bends or changes direction when it enters the prism and when it leaves the prism. This is called refraction. Different frequencies or colors of light change directions by slightly different amounts, so the red frequencies change direction less than blue frequencies. As a result, the narrow ray of white light which strikes the prism is broadened out in space according to the different frequencies contained within the white light, and we see the familiar rainbow. This is essentially how a real rainbow is produced; water droplets replace the glass prism. Have students look closely at the rainbow so that they are familiar with the colors which constitute white light (red, orange, yellow, green, blue, indigo, and violet) and so that they see how the spread of colors is continuous. Now place a colored filter, one at a time, between the slide projector and the prism. The prism will display the frequencies of light which are able to pass through the filter; observe the gaps in the rainbow for those frequencies which were not able to pass through the filter. Now students should be able to see that red passes through a red filter, blue passes through a blue filter, and green passes through a green filter. (Make a chart if it helps.)

Student Exploration:
After all of the materials are ready, each group of students should first take the red covered flashlight and shine it on a large, white piece of paper that is taped to the wall. They will observe that the color that appears is red. They will do this for all of the colors/flashlights. Now the students should shine the red, blue, and green lights together to observe that the new color is white (Note: the color may appear slightly grayish depending on the quality of your filters and/or the spectrum of light emitted by the flashlight bulb). The teacher should next ask students to explore what color light they observe when they subtract each color one at a time from the white light they created. The teacher may take oral responses from the students, or depending on the age of the students, instruct student groups to make a data table to record their findings.

Tying it all Together:
Gather groups together to share and compare results and observations. Note any discrepancies in data, and re-check using flashlights again if needed. Students should have noted that red, green, and blue light combine to make white light. Now the teacher can explain why we call these ADDITIVE primary colors! The teacher can then explain that by subtracting a primary color from white light, you can obtain yellow, magenta, or cyan. This is why these colors are called SUBTRACTIVE primary colors.

Assessment: Give each student a worksheet (see Materials ). The worksheet has circles for red, blue, and green. Students will determine where two primary colors meet and identify in the smaller circles what color is apparent.

Useful Internet Resources:
* Primary Colors of Paint, Ink, and Dyes
http://home.att.net/~jpzenger/RYBORCMY.htm

* Indiana Academic Standards
http://ideanet.doe.state.in.us/standards/welcome2.html

* Edmund Scientifics
http://www.scientificsonline.com/

Special Comments: Perhaps you were taught that the primary colors are red, yellow, and blue. Maybe your own elementary teacher thought that cyan and magenta were too difficult for you to pronounce. This simplification, however, has resulted in scientific inaccuracy, and widespread misconceptions– complicated by the fact that artists use these as the primary colors of mixing paint. However, a simple check of the color printer cartridge will reveal that cyan, magenta, and yellow are indeed used as the primary inks for printing color!