Lesson #6: Colors
Light
Lesson #6: Colors
Time frame: 60 minutes
Please write the vocabulary on the board before each lesson
Vocabulary
Prism- A prism is a wedge-shaped transparent body which causes incident light to be separated by color upon exiting
Objectives
Students will be able to
1. Understand that white light is composed of a combination of colors
2. Understand that when white light is split apart, rainbows can form
Introduction
Explain to class that color and light are related. The color of an object is derived from the type of light that the object is reflecting. Color is in light and light is in color.
Ask students why they think the sky and the ocean are blue?
After they give their answers, ask then to keep thinking about it as they do the experiments for this lesson and see if they change their minds at the end.
Focus Activity #1:Putting Colors Together to Make White Light
Give students red, blue and green folders to cover three different flashlights. Let them play with reflecting these lights on a piece of paper until they can make white light. To make a white light, they need all of these three colors overlapping in equal amounts.
They can do it by either covering each flash light with a different color folder and then shinning the light on a white paper or by covering the flashlight with all the folders at the same time.
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Activity #2: Separating the Colors out of Light
If it is nice day:
Make a rainbow – with light and water droplets. Use a garden hose outside in bright sunlight. Spray a fine mist into the air. Where should you stand to see a rainbow? Ask the students what they are seeing when they see a rainbow? (Answer: they are separating the colors that comprise the white light – the exact opposite of what they did in Activity #1)
If it is not a nice day:
1. Hold a prism between sunlight and a wall. (An overhead light bulb can be used in place of the sun.) Turn it until you see a “rainbow” on the wall.
2. Put a box in front of a prism or a clear rectangular plastic container filled with water. Shine a flashlight through the slit of the provided box. The narrow beam of light should hit the prism or water at a small angle. A rainbow will appear beyond the prism or container. Which color is bent the most? Which color bends the least? Try this out with different prisms!
(Refer to drawing on Page 27 in Dazzling Science Projects with Light and Color)
Concepts
To see a rainbow, the sun must be behind you. To find out why, you need to know how a rainbow is made. Raindrops are like tiny lenses – like tiny glasses. Sunlight entering a raindrop is bent – like we learned last class. Violet light bends more than red light. Some of the bent light is reflected inside the raindrops. The reflected light bends again as it leaves the raindrop. Your eyes receive red light from higher drops and violet light from lower drops. This is why you see red at the top of a rainbow and violet at the bottom.
Water, glass and plastic all bend violet light more than red light. In between are blue, green, yellow, and orange. These colors all have different properties and can be organized into a spectrum – a rainbow of colors.
Raindrops bend light twice. You bent light two times in each experiment that you did. Refracting light twice makes a better spectrum because the colors spread out more each time the light is bent.
A spectrum can be made by bending – refracting – any white light. It does not have to be sunlight. An ordinary bulb will do.
Conclusion
Why is the ocean and sky blue?
The ocean looks blue because red, orange and yellow (long wavelength light) are absorbed more strongly by water than is blue (short wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. This is the same reason for why the sky is blue.
The color of the ocean and the color of the sky are related but occur independently of each other: in both cases preferential absorption of long-wavelength (reddish) light gives rise to the blue color. Note that this effect only works if the water is pure; if the water is full of mud, algae or other impurities, the light scatters off of these impurities, which will overwhelm the water’s natural blueness.
*For all light lessons, if there is extra time at the end, have the students use the “Bobo explores light” application on the iPad