Water Rainbow
How Do Water and Sunlight Create a Rainbow?
Materials
- clear plastic cup
- tap water
- sheet of white paper
You must have access to a sunny windowsill.
Try This
- Fill the plastic cup with tap water.
- Place the cup of water on a windowsill in bright sunshine so the cup extends over the ledge a little. Balance the cup so it will not tip over.
- Place the sheet of paper on the floor where the sunlight falls. What do you see on the paper?
- Write the name of each color next to the color on the paper.
What's Going On?
A rainbow appeared on the sheet of paper. Although sunlight seems to be white, it is actually made up of a combination of all colors. As light passed through the water in the cup, the light rays of each color bent in a slightly different direction. This is because different colors have different wavelengths, which means they interact with the medium they are traveling through in differing amounts. Imagine swimming across a river. If you swim straight across, coming up for air rarely, the current of the river doesn't push you downstream that far. If you swim across just as quickly, but bob up and down more often to come up for air, the current of the river has more of an opportunity to push on your body, and you end up reaching the other bank farther downstream.
When the white light from outside passes through the water, the different color wavelengths interact with the water in differing amounts, and so turn different degrees, causing them to spread across the paper.
Notice the order of the colors of the spectrum, or series of color bands; and, with the aid of your paper, try and remember the order.
