Light Matters

Learning Objectives

The object of this activity is for students to investigate the ways in which light interacts with every day objects, and to acquaint themselves with the necessary vocabulary for describing these interactions.

Materials

• A book
• 1 clear glass filled with water
• 1 clear empty glass
• Sheets of wax paper
• Aluminum foil (try to minimize creases)
• Magnifying glass
• Pencil (to be placed in the glass with water in it)

Motivation

Light is one of the most fundamental elements of our everyday experiences, largely because it is the mechanism by which we see. Light is very interesting because it interacts with matter in a relatively limited number of ways. The first is reflection. This is when all incoming rays of light are bounced back the way they came in. An example of this is a mirror, or a sheet of aluminum foil. Refraction is when the paths of the light rays get bent. One example is the shimmering that occurs above a barbeque, and another example is the way that a magnifying glass increases the size of objects underneath it

Translucent materials are ones through which some light gets through, but some of it does not. Translucent materials are excellent places to discuss the ideas of transmission and absorption, because of this property of theirs. Transmitted light is the light which can get from one side of the object to the other, and absorbed light is that which does not. As an example, consider wax paper. When you hold wax paper up to a light, you can see that some of it gets through to your eyes. This is the transmitted light. You can also see that, that the image of the light behind is not as clear as if you were looking directly at it. That is because the light that would complete the picture is being absorbed.

Transparent materials are ones that do not bend or change the light going through them at all. The most immediate example of a transparent material is air. Another would be plate glass. Though the glass does cause some bending of the light rays that pass through it, because it is flat (and as long as it’s not too dirty) still perceive it as being transparent.

Opaque objects absorb all the light that is incident on them. Opaque objects are probably the most familiar. Objects made of cloth, wood, and cardboard are all opaque. You cannot see through opaque objects at all.

Procedure

Part 1

This activity is an exercise in some of the definitions associated with the way that light interacts with matter. Words that the students will become familiar with are: Transparent, translucent, opaque, reflection, and refraction, transmission and absorption. Part 1 of this activity is simply to introduce these concepts before the students sit down with the worksheet.

Part 2

Put the pencil into the glass of water. Make sure students have a look at the pencil through the glass from straight on, and from an angle as well. With the materials in front of them, have the students try and produce examples of systems that reflect, refract and absorb (opaqueness) light, and also find examples of systems that are transparent.

Topics for Discussion

• What is transmission? What is absorption?
• What is reflection? What is refraction?
• What kinds of materials are transparent? Reflective? Opaque?
• What sort of technologies take advantage of the way light interacts with matter? (Magnifying glasses, telescopes, cameras, kaleidoscopes, laser tag