To explore light and color, including how colors are mixed to produce new colors, how light is filtered, and how light is reflected off of surfaces.
Many middle-school students do not think of light as something that travels from one place to another, and most tend to identify light with its source (e.g., light is in the bulb) or its effects (e.g., a patch of light). As a result, students have difficulty explaining the direction and formation of shadows, as well as reflection of light by objects.
Middle-school students usually understand that mirrors reflect light, but have a hard time believing that of objects which do not reflect their image. Many students do not believe that their eyes actually receive light when looking at an object. Students' ideas of vision vary from the notion that light fills space and the eye sees without anything linking it to the object, to the idea that light illuminates surfaces that we can see by the action of our eyes upon them. The notion that the eye can see without a link to the object is a notion that can even persist after basic instruction in optics. (Benchmarks for Science Literacy, pp. 338-339.)
There are three Science NetLinks lessons in this series on light:
Light 1: This lesson is an introduction to light, preparing students to address issues like those discussed above. This lesson introduces students to the electromagnetic spectrum (focusing on visible light) and the wave nature of light.
Light 2: This lesson focuses on the idea that we can see objects because they either emit or reflect light. It discusses the way light is reflected, absorbed, and scattered to allow certain wavelengths to reach the eye, leading to a perception of different colors. It is an introductory exploration and would be best if complemented with hands-on activities.
Light 3: This lesson includes an Internet exploration that focuses on the roles of the eye and brain in the perception of color. It includes an introduction to the anatomy of the eye, including the functions of rods and cones.
It is recommended that you complete the first Science NetLinks lesson in this series, Light 1: Making Light of Science, before this one. Ask these questions to review basic concepts necessary for this lesson:
- What is the electromagnetic spectrum? (It is the entire range of all kinds of light, including light the human eye cannot see.)
- What is the region of light we can see called? (Visible light.)
- Give examples of light we cannot see. (Examples include X rays and radio signals.)
- How is a rainbow formed in nature? By a prism? (In nature, raindrops break sunlight into the visible spectrum. A prism does the same thing, breaking white light into the visible spectrum.)
In this section, students will read information online and answer questions on the student sheet, The Lighter Side of Color. Depending on the number of available computers, students could work alone or in small groups. It would be best if you could complement the Internet exploration with hands-on activities with light and filters.
Distribute the student sheet and have students complete Part I. As outlined on the student sheet, students will view a slideshow, The Lighter Side of Color, from the Tech Museum, and answer questions. After students finish, discuss the questions listed on the student sheet in class:
- What happens when you mix colors? (Mixing two colors will produce a third color. For example, green and blue make cyan; red and green make yellow; and red and blue make magenta.)
- What do dyes (pigments) do in terms of letting light through? (They let certain colors pass through and absorb others.)
- How do filters work? (Filters work by trapping some wavelengths of light while letting others pass through. For example, a red filter will trap blue and green light, but allow red light to pass through.)
- Now think of light other than white light. What happens if you pass magenta light through a red filter? (The blue light is trapped, and the red light passes through.)
- Give an example from the reading where a colored filter blocked light completely. (When green light is shone in a red filter, all the green light is grabbed and there is nothing left.)
- How do fluorescent dyes work? (They can absorb light, change it into a longer wavelength, and send it out in all directions.)
- What are some "sources" of light? (Examples include the sun, fluorescent lights, and incandescent bulbs.)
- What happens when you look at an object in different light? (Its color may change.)
- In what ways can light be reflected when it hits a surface? Include diagrams of light reflecting off of a smooth, rough, and in-between surface. (If the surface is smooth, the light is reflected at the same angle it came in. If the surface is rough, the light is scattered in all directions. When the surface is somewhere in-between, it reflects light close to the same angle it came in.)
- Explain why you sometimes get a glare when reading a magazine. (Magazines often use smooth paper that acts like a mirror. You get a glare if the light comes from the wrong angle.)
- Would it be possible for dyes to absorb all of the light hitting a piece of paper? If so, what color would that paper be? (Yes, the paper would be black.)
Use the student sheets and class discussion to assess student understanding. In addition, have students complete the following activity:
Give each student (or group of students) a mirror, a piece of shiny metal (aluminum foil works well), a piece of colored paper (red, green, or blue), and a piece of black paper. Have them examine each object, and then answer the questions on Part II of their student sheet:
- When you look at each item, what do you see? (Answers will vary, but should include the fact that they see their own reflection in the mirror.)
- Which ones reflect light? (Most likely they will say that the mirror and the shiny metal reflect light and the papers do not.)
- Do they reflect light the same way? Explain. (No, the mirror reflects more light.)
- How did each object reflect the light? (The mirror reflects the light at the same angle, not scattering it at all. The metal and the paper both scatter the light a little.)
- Which objects absorb light? (Paper.)
- Which colors were reflected from the piece of colored paper? Which were absorbed? (The color of the paper was reflected, while other colors were absorbed.)
- Do any of the objects produce light? (No.)
- If they do not produce light, how can we see them? (Light from the room is reflected off of the surface to our eyes.)
- The light that is hitting the surface of the colored paper is white; why does the paper look the color that it is? (The dyes in the paper are absorbing some wavelengths of light. The color that we see is the color reflected.)
Complete the third Science NetLinks lesson in this series:
To explore the way humans look at light, shadow, and images, have students visit Bob Miller's Light Walk from the Exploratorium.