BioEd Online

Teacher Background

Light that we can see is just part of the entire spectrum of radiation produced by the sun (electromagnetic radiation). The sun bombards Earth with radiation of many different wavelengths at the same time. Some radiation emitted by the sun can be classified as infrared (which we feel as heat) or visible (which we see as light and color). However, the sun also produces higher energy radiation, such as ultraviolet (UV) radiation, x-rays, and gamma rays.

Radiation from the sun, including light, behaves as if it travels in waves. The distance between wave crests (wavelength) and the speed with which they pass a fixed point (frequency) are related to the amount of energy contained in photons (basic units of light) that make up the wave. Radiation of shorter wavelengths (which travel at higher frequencies) has more energy than radiation of longer wavelengths. Visible light falls between the longer wavelengths of infrared radiation and shorter, higher-energy wavelengths of UV radiation.

Visible light consists of a mix of wavelengths that we detect as different colors. We can see these colors when white light (light as we usually see it) passes through a prism—or drops of water—and forms a rainbow.

The colors of the rainbow always appear in the same order because they correspond to different wavelengths of light. You may have learned the acronym “ROY G. BIV” to help you remember the colors of the rainbow from longest to shortest wavelengths: red, orange, yellow, green, blue, indigo, and violet.

Objectives and Standards

Concepts

• Visible light is composed of many different wavelengths of radiation.

• We can see different wavelengths of light as the colors of the spectrum.

Science, Health, and Math Skills

• Observing

• Predicting

• Identifying patterns

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

• two 9-oz clear plastic cups (or clear glass jars or glasses)

• clear beaker, 1,000-mL size (or qt-sized glass jar or other clear container)

• overhead projector

Materials per Student

• crayons or colored markers

• sheet of white paper

Setup

1. This activity requires no prior preparation. However, for dramatic effect, you may want to set it up while students are out of the classroom for lunch or another activity.

2. Have students work in groups to share materials as they create their own rainbow designs.

Procedure and Extensions

1. Fill a clear, liter-sized glass or plastic container with water and place it on the lighted “stage” of an overhead projector.

2. Darken the classroom as much as possible. You and your students will be able to observe a circular rainbow projected around the classroom.

3. Allow a few moments for students to observe the rainbow. Ask, Have you ever seen anything like this before? Students will provide a variety of responses. Follow by asking, Do you think the colors are the same in every rainbow?

4. After students have shared or written their predictions, place another, smaller cup or glass filled with water on the overhead. Have students observe and compare the sequence of colors in the rainbow produced by the second cup.

5. Repeat with a second cup or glass of water. Repeat the question, Do you think think the colors are the same in every rainbow? Make sure students are able to observe that the sequence of colors always follows the same pattern. With older students, explain that the colors of light represent energy of different wavelengths.

6. Have students identify the source of light for the rainbow (white light from the overhead projector). Then, help them understand that the light is being separated into its constituent colors as it passes through the water in the container.

7. Let each student make his or her own rainbow drawing that incorporates the sequence of colors observed in the classroom rainbow. Display the rainbow drawings.

Extensions

• Conduct further explorations of the spectrum by using prisms outside with sunlight and/or indoors with light from incandescent or fluorescent bulbs.

• Help students understand waves by modeling wave motion with a spring toy (“slinky”). Lay the spring on a table top and wave one end from side to side. Students will be able to see waves move along the length of the spring.

• Explore the vast differences among wavelengths in the electromagnetic spectrum by measuring out the lengths of some of the following kinds of waves in the classroom and/or on the playground:
  
  100 m: AM radio waves
  10 m: FM radio waves
  1 m: television waves
  1 cm: microwaves, such as those used to cook food
  Less than 1 mm: infrared waves, felt as heat

• Printers use cyan, magenta, yellow, and black inks to create all the colors in a printed document. Have students examine color photographs, comics, or advertisements printed in the newspaper, using a hand lens or magnifier. Have them identify the combinations of colored dots used to create colors such as orange, green, and purple.

Handouts and Downloads