Rainbow science fair projects are appropriate for younger children, especially those in early elementary school. Kids can experiment with light to make their own rainbow or use the science fair project to explain all of the properties of rainbows.
Make a Rainbow
For this science fair project, you can help your child make a rainbow and observe properties of it. Since a rainbow is simply refracted light, you can make a rainbow in a variety of ways. Have your child write down the purpose of this experiment, along with a hypothesis. With your child, create rainbows by holding the backs of CDs or DVDs up to a light source, filling up a water glass and placing it in direct sunlight, shining a flashlight through the glass of water or purchasing prisms and playing with the different reflections they make. Have your child right down her observations.
Rainbow in a Bottle
For this project, you'll need some special equipment. This experiment, however, is special because it is the same one Sir Isaac Newton did when discovering properties of light. With your child, fill up a fishbowl or glass three-fourths of the way. Submerge a small hand mirror in the water, and balance it on the side of the glass. With one hand, hold up a white piece of cardboard in front of the mirror, and with the other hand, shine a flashlight into the mirror. You've created a rainbow in a bottle that will reflect on the cardboard paper.
For this project, merely have your child research all about rainbows and their properties. He can purchase a tri-fold board and post small bits of information on the board, such as diagrams of rainbows, different types of rainbows and fun and interesting facts about rainbows in literature and in culture and folklore. He can also use his tri-fold poster and diagrams to explain, in detail, the process of refraction.