Lesson 3: 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.

As you know, the primary colors of light are red, blue, and green; 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: Be sure to save the rest of the food coloring, which will be used in the next science unit.
Student Activity Page
NOTE: Be sure to save the rest of the food coloring, which will be used in the next science unit.

Here your child will investigate what happens when colors of paint are mixed compared to when colors of light are mixed. When he finishes, discuss how when the colors of water were mixed, the water got darker. But, when colors of light are mixed, they get lighter.

Show your child the following graphic. Tell him that light travels in waves and that each color is actually a different sized wave. Explain that we are able to see colors in clothing and other products because they absorb and reflect parts of white light. The things that determine what color we see are called pigments. So why does red paint look red? Well, the pigments in red paint absorb all wavelengths of light except for red. The red wavelength is reflected off of the paint onto our eyes so we see the paint as red. As you mix paint colors together, there will be more and more wavelengths of light absorbed by the mix of pigments in the paint. This also means there are fewer wavelengths of light (or colors) to get reflected to our eyes. Eventually, if every wavelength was absorbed after mixing pigments together, you would see black because there is no light left to be reflected off of the object to our eyes. This type of color mixing is called "subtractive color mixing" because colors of light are being subtracted as more wavelengths are absorbed by the different colored pigments.

What about light? Why did it get lighter when the colored flashlights mixed? Since we are talking about the SOURCE of the light, instead of the object reflecting the light (like paint), mixing colors of light looks different. This type of color mixing is called "additive color mixing." In this case, as you add more wavelengths of light together, it will get lighter and lighter. So it makes sense why, in Activity 3, mixing the three different colors made white light.

Refer to the following image at the following web link to see the difference between additive and subtractive color mixing.
Web Link

Activity 5: Color Wheels

Materials: alligator clips (kit), battery (kit), color wheel (kit), colored pencils, motor (kit), pencil, rubber bands (kit), scissors, tape
For this activity you will design a color wheel, attach it to a motor, and spin it. What color do you think you will see? Why?

Follow these steps:
  1. Cut out one of the color wheels found in your science kit.
  2. Use colored pencils to color the sections in this order: red, orange, yellow, green, blue, purple.
  3. Next, set up the motor. Put a rubber band around the battery so that it is centered over the ends. Attach an alligator clip to the rubber band so that one side of the clip is touching the center of one end of the battery. Attach the other alligator clip to the other end of the battery.
  4. Connect the other end of both clips to the wires of the motor. (See diagram.) The motor should begin to run, and the shaft (the piece of metal sticking out from the motor) should begin to spin. Turn off the motor by unhooking the wires.
  5. Put a piece of tape over the dot in the center of the wheel. Flip the wheel over and put a piece of tape on the back side too.
  6. Poke a small hole through the dot on the wheel with something sharp, like a pencil, needle, or nail.
  7. Now poke the shaft through the center of the wheel, with the colored side of the wheel facing up. The fit should be tight so that the wheel does not spin freely around the shaft. If the wheel is loose, tape the wheel to the shaft more securely. You may want to do this on the back side of the wheel.
  8. Hook the motor back up and watch the color wheel spin.
What did you see?

What do you think would happen if you used different colors (e.g. yellow, purple, and orange)? Try different combinations of colors on the remaining color wheels. You can use as many or as few colors as you want on each wheel.

Discuss your results with your parent.

NOTE: Be sure to keep one color wheel as well as the motor, alligator clips, and battery. You will use them again in Lesson 4.
Your child will set up a simple motor to spin a color wheel. Assist as needed. As the color wheel with all the colors of the rainbow spins, your child should see a white-ish blur. When he finishes investigating his color wheels, explain that when the color wheel spins, his eyes are averaging all of the colors, and white is made up of all the colors.

His eyes do the same thing when he watches TV or uses any sort of phone or computer screen. Screens work by projecting light, which our eyes translate into the colors and images we see on the screen. The pixels on a screen are made of the primary colors of light: red, blue, and green. By changing the percentage and intensity of pixels, a screen can show almost any color. You can show your child the following video, which shows an extremely magnified view of pixels. If your child looks closely, he will see the red, green, and blue sections of each pixel.
Web Link

Activity 6: Light Travels

Materials: clay (kit), flashlights (kit), note cards (kit), piece of cardboard (kit), ruler, scissors
What path do you think light takes as it travels from one place to another? Does it move back and forth? Spread out like a fan? Is it crooked? Follow the directions for this experiment on the "Light Travels" activity page.
Student Activity Page
Review the fact that light travels in a straight line from a light source. When it hits a surface it is blocked, because it is either being reflected or absorbed. Your child will explore reflection and absorption in the next activity.