Light rays travel at different speeds through different substances. When light moves from one material to another, the change in speed as it slows down or speeds up causes the light rays to bend. This bending is called refraction. Some substances, such as water or certain shapes of glass, can bend light rays so that the white light we normally see is separated into the colours of the rainbow. You can demonstrate and explore the refraction of light with simple activities.
The way objects look when in water or viewed through water is an illustration of light refraction. Use plain drinking glasses or round jars with smooth sides for best results. Stand a pencil in a glass container and look through the side of the container at it, noting that the pencil looks straight. Then fill the container half-full with water. When you look through the side, you will see a displacement at the water line, making it look as though the pencil bends or is even broken into two pieces.
Place parallel lines several inches long on a flat surface. Use at least three different colours. Marker on paper will work, but coloured tape on a board or other smooth surface will stand up best to accidental spills. Place a glass or jar on the lines. Look through the glass at the lines on the other side, observing where they emerge from under the glass. Fill the glass with water and observe again. You will see that the lines behind the water-filled glass appear to bend to one side or the other. Depending on the size of your jar and lines, you may also see that the lines are apparently split or displaced to one side or the other when viewed through the water.
Rainbows are the colours produced by refracted light. To create a rainbow outdoors, use a sprinkler. Set the sprinkler to produce a fine spray. Walk around the mist, looking through it to find where you see a rainbow. Also look at objects around the sprinkler to find other rainbows.
Make a rainbow indoors with a glass of water. Set the glass on a sunny windowsill or a table in front of a sunny window. Look at the floor in front of the windowsill or table to find where a rainbow appears. Place a white sheet of paper on the floor where the rainbow is to see it in more detail. Use a flashlight in a darkened room instead of sunlight for a variation on this activity.
Prisms are multi-sided pieces of glass that refract light. Place a three-sided prism in a beam of sunlight and move it around to see the colours produced on the surfaces where the light through the prism falls.
Place a prism on a newspaper or other printed page. Try reading through different surfaces of the prism to see how the type looks from different angles. Use a prism in the same way on pictures or photographs.