Lesson 2: Light

Day 2

Activity 4: Colors

Materials: clear cups (kit), measuring spoons, red, blue, and yellow food coloring (kit)
Have you ever wondered why our eyes see things in different colors? When light travels from an object and enters our eye, we can see the object. The light that is reflected from the object determines the color we see. A blue object appears blue because when white light shines on it, the object absorbs all other colors except blue. It reflects the color blue.

What do you think happens if an object absorbs all the colors of the rainbow and reflects none of them? As you know, the primary colors of light are green, red, and blue; but the primary colors of pigments (solid or liquid forms of color, like paint) are red, blue, and yellow. Mixing colors with paint or food coloring produces a different outcome than when you mix different colors of light. Conduct the investigation described on the "Colors" activity page.

NOTE: When you are done, rinse out the cups and save them for use in Lesson 4. Also save the food coloring, which will be used in the next science unit.
Student Activity Page
Here your child will investigate what happens when colors are mixed compared to when colors of light are mixed. When she finishes, discuss that when the colors or water were mixed, the water got darker. This is the opposite of what happens when you mix the colors of light — you get white light.

Explain that we are able to see colors in clothing and other products because they absorb and reflect parts of white light. These colors, for example paint colors, act differently than colors of light. The primary colors of light are green, red, and blue. The primary colors of pigments, like paint, are red, yellow, and blue. When you mix a lot of colors together, you are actually reducing the colors of light that are reflected from the object, like a jar of paint. More colors added to the jar means more colors of light are absorbed, so fewer colors are reflected. Fewer colors reflected means there is an absence of color available for us to see. The absence of color is black.

NOTE: Ask your child to rinse out the cups used in this activity and save them for use in Lesson 4.

Activity 5: Reflection and Absorption

Materials: dark cloth (kit), flashlights (kit), mirror (kit), piece of cardboard (kit), piece of white paper (kit), piece of wood (kit), tape, white paper
Things that make light are called light sources. Things that are not light sources give off light by absorbing some light colors and reflecting others. A blue object appears blue because it absorbs all colors except blue. A yellow object absorbs blue light but reflects red and green light (red and green light make yellow).

Reflection occurs when light bounces off of objects. The amount of light reflected off of an object depends on whether the surface is rough or smooth. On a rough surface the light scatters, but if a surface is smooth and flat, the light will bounce off it at equal angles.
Gather the materials listed on the "Reflection and Absorption" page, and find a room that can be darkened (by closing curtains or turning off a light). Perform the following two tests.

Test 1:

  1. Place the cardboard, fabric, wood, and paper in a row on the floor or on a flat surface.
  2. Darken the room.
  3. Shine a flashlight onto each material, one at a time. Make sure you are about the same distance from each of them.
  4. Notice what color you see for each object, and record your results on the activity page.
  5. Decide whether the objects are reflecting or absorbing light, or both. If something absorbs all the colors of the rainbow and reflects none, you will see black. If something reflects all of the colors and absorbs none, you will see white. If you see a color other than black, you know your item absorbs some colors and reflects others. Record your results on the activity page.

Test 2:

  1. Line up the mirror, cardboard, fabric, wood, and paper in a row on the floor. Space the objects about 6 inches apart from each other, and 6-12 inches from an empty wall, as shown in the following illustration.
  1. Tape white paper to the wall behind each object, a few inches above the floor.
  2. Darken the room.
  3. Shine the flashlight at an angle on the mirror.
  4. On the activity page, draw the angles you observe for light coming from the flashlight toward the mirror and the angles of the light going away from the mirror toward the wall. The following illustration is an example of how you might draw the mirror's angle of light on the activity page.
  1. As you draw, notice how bright or dim the light on the wall is, and how spread out the light is. Use arrows of different sizes and weight to communicate these details as well as to capture the angles of the beams of light. For example, the mirror will have a bright, focused beam, so your may show that by drawing a single arrow that is thick and dark.
  2. Keep the angle of the flashlight the same and repeat for the other four objects. Unlike with the mirror, it will be hard to see exactly where the light is reflecting onto the wall. To get an idea of where the light is reflecting, you might want to change the angle of the flashlight and watch what happens to the light on the wall. Return to the original angle before drawing your pictures. In your drawings, remember to show these three things: how bright or dim the light on the wall is, how spread out the light on the wall is, and the angles of the beams of light.
  3. Answer the question at the bottom of the activity page and discuss your findings with a parent.
Student Activity Page
Discuss which surfaces reflected more light and which absorbed more light. Discuss whether some objects absorbed some light and reflected other colors of light. Analyze the angles your child observed, and discuss whether some of the light on the wall may have been reflected from the surface the objects were sitting on.

For Test 1, your child should note that the white paper reflected all light and the dark/black fabric absorbed all light. Because they look brown (and not white or black), the cardboard and wood both absorbed and reflected light.

For Test 2, results will vary. Your child should have noticed that the angle that the light travelled from the object to the wall changed depending on the angle from the flashlight to the object. The smoother the surface of the object, the more the light was all reflected at the same angle. The light hitting the wall from the mirror was much more highly focused than the light reflecting from the paper, cardboard, fabric, and wood. The wood and dark fabric may seem to reflect very little light toward the wall because their irregular surfaces scatter the light in many directions rather than staying focused in a beam. Your child may also notice that the darker colored objects reflected less light because they absorbed more light. In general, your child should notice that the amount of light reflected onto the wall, from most to least, will be similar to this: mirror, white paper, wood and cardboard, fabric.

Activity 6: Color Wheels

Materials: card stock*, color wheel card (kit), compass*, markers, pencil, protractor*, ruler*, scissors
For this activity you will design a color wheel according to the following directions:
  1. Cut out the color wheel found in your science kit. (If you do not have a color wheel card, using a ruler and compass, cut a four-inch diameter circle from card stock paper and then use a protractor to draw three equal pieces -- each measuring 120 degrees -- on the circle.)
  2. Color the pieces red, green, and blue.
  3. Put a sharpened pencil through the center of the circle and spin it. It may help to place the tip of the pencil against a desk or book with one hand, and then use your other hand to spin the circle.
  4. If you spin the card fast enough, you should see a white blur.
Did you see the white blur?

What do you think would happen if you used different colors (e.g. yellow, purple, and orange)? Why do you think it would look different? Ask your parent to explain why.
When your child finishes investigating her color wheels, explain that her eyes are averaging all of the colors and white light consists of all of the colors. Red, green, and blue are the primary colors of light. If you have a TV, you can use it in a couple of ways to demonstrate this. First, let your child use a magnifying glass to look at a TV that is playing. The areas of the screen that are white will have tiny pixels that are red, blue, or green. The mind averages these to get white. By changing the percentage and intensity of pixels of any given color, the TV can show almost any color on the screen.