Rainbows and color mixing are lovely messy science and art blended together. Most of the work here is color mixing and this one can get nice and messy. You can use water color paints or bath tub tints to make different colors.
Color Mixing - using color bath tablets, make containers with three primary colors: red, blue and yellow. Primary colors cannot be made by mixing. Watch the tables. What happens when you put them in water? Pour some of the yellow into another container. What will happen if we add a few drops of red? (orange) Pour some of the red into another container. What will happen if we put in a few drops of blue? (purple) Pour some of the blue into another container. What will happen if we add a few drops of yellow? (green - tho this might be easier the other way around - add the drops of blue to yellow)
You can see how we did color last year here.
To take the lesson up to older students, we worked on tertiary colors - colors that blend one primary and one secondary color. While most color wheels have rather flat names for these like yellow orange and blue violet, you can make up lovely names for them like stormy ocean, or Arizona sunset.
Spectrometer - a spectrometer measures the changes in the spectrum and can be used to identify different materials. It is pretty simple to make one. Here are directions to making your own. You can use it to look at different types of light like flashlights and candles or try putting a bit of table salt in to a flame and see how the spectrum changes.
Why are rainbows curved? This is a great question to ask older students. On a sunny day, put a glass of water in a window and move it until you have a rainbow. You can also use a CD. Both of these will produce a straight spectrum -no curve. Why is a rainbow curved?
Light travels in a straight line. As it enters the raindrop (or any drop of water) it splits up into its color components (colors of a rainbow). Most of the light travels right thru the water drop. Some reflects or bounces back thru the drop. The sides of a water drop are curved so the resulting reflection is also curved. The CD and water glass are straight, so the resulting spectrum is also straight. (The light is reflected of the glass vertically so it isn't curved to the light. Knew you'd ask!!)
What have you been doing with color science? Post your thoughts and comments.