Science Bus Fall 2005

Week #3, Mike Preiner and Kai-Mei Fu

Quarter’s Theme: Light, color and the eye

Week’s lesson:

Colors

Grades: 2-3, 4-5

Goals:

2-3rd: To learn that white light is (usually) made up of the entire color spectrum.

4th-5th: Same as above. Also, to learn color addition.

Outline: 5 minute lecture. Each tutor will take 2-4 students around to different stations that explore how light works. Before starting the lessons, make sure each tutor knows which station they are responsible for setting up. Each tutor should work at the level of the students they are with. It is great to just let the students explore and ask questions and not get too technical. Feel free to stay as long as you like at each station. You do not need to complete them all. Move on to any station that is available.

NOTE: All of the lights will be off in the classroom for the entire lesson. Also, we will have a few spectrum posters around to illustrate how light is actually made up of different colors.

Each station has 2 copies of the experiment. Keep your group at ONE of the experiments so it is possible for two sets of kids to work at one station.

Lecture (5 minutes):

Remind the students that this quarter in Science Bus we are studying light. Today we will be studying color.

Ask the students to name some colors. Then hold up a white LED and ask them what color it is. They will probably say white. Then ask them what will color they will see if you hold up a red filter in front of it (and do it). They will see red. Then ask them what will happen if you hold up a blue filter in front of it (and do it). They will see blue. Then ask them what will happen if you hold BOTH filters in front of the LED. They will probably give a hundred different answers. Do it. They will see nothing. Tell them that today we will be learning about how colors add and subtract.

Reference: Activity 1:

Title: What colors are in white light? What colors are in red laser light?

Goal: Confirm that white light is made up of all different colors by shining white light though different color filters. Demonstrate that laser light is special. It is truly only ONE color.

Reference: none

Materials:

  • Filters
  • Red laser pointer
  • Flashlight (not LED!)

Procedure:

The tutor should be in charge of holding the filter stack since it is difficult to isolate the filters (at least for 2-3rd grades). When using the filters, fold filter in half (but do not crease). This provides a much better extinction ratio!

Tell the students that we are going to be working with special colored pieces of plastic called filters. Hold up a blue filter. Ask what color it is. (blue) Ask why it is blue. Don’t let the students struggle too much on this one. Explain to them using the visible spectrum sheet that the blue filter blocks all the other colors except blue. Ask them to name a color. Shine the flashlight through the corresponding filter. The light out is always the same color as the filter.

Ask them what colors are in white light, or the flashlight. (Answer, all colors because all colors make it through the filter).

Next bring out the red laser. Explain that lasers are very different from flashlights because they are only one color. Go through the same experiment as above except with the red laser! The student should discover that shining the red laser through red filters gives red light. Shining the red laser through blue filters makes NO light!

Optional: You can combine filters. Use the red and blue to completely block the light. Use the blue and yellow to make green.

Activity 2:

Title: Why is the sunset red (and the sky blue)?

Goal: To understand the following concept: Blue light scatters more than red light, or, white light turns red if it passes through a bunch of scatters.

Reference: none

Materials:

  • Clear plastic container
  • Powdered Milk
  • Measuring spoon
  • Stirring spoon
  • Flashlight

Procedure:

Turn on the flashlight and the ask the kids what color it is (white). Fill up the clear plastic container with water. Ask the kids what color they will see if they look at the flashlight through the water. It will look just like it did before. Ask the kids what color the sun is. They will probably say yellow. Then ask them what color the sky is (blue). Ask them if they have ever seen the sky another color. Hopefully they will have seen a red sunset. Tell them we are going to do an experiment to see why the sky is blue and sometimes red.

Have them look at the flashlight again through the water. Now tell them that the sky (atmosphere) is made up of air molecules and dust, and we are going to add something similar to the water. Have them put in a TINY bit (~1/8 to ¼ tsp) of powdered milk to the water. Have them stir it into the water. Now have them look at the flashlight from the side and from the far end of the tank. It will look pretty similar to before. Have them add some more powdered milk. Eventually the flashlight will look blue from the side and red from the far end of the tank. Keep adding milk, and no light will get through the tank. The light looks blue (blue-ish white) next close to the flashlight because blue light scatters more strongly than red light, so it scatters off to the side right away. Soon all that is left of the light is the red component, so the light looks red at the end of the box. The same process makes the sky blue (sunlight scatters down to your eye off of the atmosphere), and when the sun sets, all of the blue gets scattered away, and all that is left is red.

Activity 3:

Title: LEDS and diffraction gratings.

Goal: Demonstrate that a white LED is actually made up of several different colors, while blue and green LEDs are not.

Reference: none

Materials:

  • LEDS (white, blue and green)
  • Small diffraction gratings

Procedure:

Ask the kids what color the white LED is. Then ask them why it is that color. Don’t let the students struggle too much on this one. Explain to them (possibly using the visible spectrum sheet) that the LED is white because it is made up of several different colors. Explain to them that it is possible to split white light into its component colors. Give them the small diffraction grating and have them look at the white LED. Ask them what they see (a bunch of different colors). Ask them where all of the different colors (blue, green, red, etc) come from. Ask them if they see any white (other than the white LED). They shouldn’t. Ask them why. Have them look at the blue and green LEDs and try to figure out why the diffraction patterns show only blue and green, respectively (the LED’s aren’t pure, so they will still show a bit of other color).

Bonus: Show them the CD, and explain that it scatters light just like the little gratings. Have them shine a white LED at it (they will get many colors out). Have them shine the blue and green LEDs at it. They will get mostly blue and green.

Activity 4:

Title: Color lamps

Goal: Demonstrate that different color light can be added together to make new colors.

Reference: none

Materials:

  • Color lamps
  • White paper and notecards

Procedure:

Set up one of the color lamps so that it is projecting onto a white piece of paper ~3 feet away. It will have red, green and blue sections. Turn on one of the other color lamps, and ask the kids what will happen when you put one set of colors on top of the others. Go ahead and do it. Line up the red on top of the blue. Ask them about the color combinations that they see. Turn on the third lamp, and ask them what they will see when you line up red, blue, and green (it should look white). Now let them play with blocking various colors and trying to figure out how the colors add.

Activity 5:

Title: Color Wheels

Goal: Demonstrate that different color light can be added together to make new colors.

Reference: none

Materials:

  • Colored wheels
  • Pencils
  • Markers
  • Ruler
  • Index Cards

Procedure:

Have the kids look at the color wheels (they are either red/blue or yellow/green). Ask them what color they are. Ask them if they know what happens when you add the two colors (red/blue or yellow/green). Now spin the color wheel, and watch the colors merge together. Ask them why they think this happens.

They can now make their own! First, draw out a 3” diameter circle on a notecard (either white or colored). Then cut it out. Then, draw 8 equal sections in the circle. Have the students pick two colors (or 1 color +colored notecard), and fill the sections in with alternating colors. We should have enough pencils for them to take them home.

Activity 6:

Title: Adding Colors

Goal: Demonstrate that different color light can be added together to make new colors.

Reference: none

Materials:

  • 3 cups of food-colored water: red, blue and green
  • Cups for the students
  • Cups for waste
  • Water
  • Food coloring
  • Straws

Procedure:

Using the straw as a pipette, have the students put drops of colored water from the cups. Let them play with making different colors. See if they can make specific colors.