Demonstrate the index of refraction by making glass rods disappear when placed in a liquid. Fill two glass containers halfway with water and vegetable oil, respectively. Place two glass rods in each container and ask students to observe them through the side of the container. The rods in the oil should disappear because the index of refraction of the rod is similar to that of the oil.
When a pair of jeans gets wet, the fabric looks darker. This results from the water changing the index of refraction of the jeans. Because the index of refraction of water is close to that of air, wet jeans reflect less light and look darker. Before demonstrating, ask students to predict what will happen when the pair of jeans gets wet. Try the activity with other types of materials, such as paper, sand and non-absorbent material like plastic.
Every liquid has a different index of refraction. Fill three opaque glass bowls with one of three liquids -- rubbing alcohol, water or vegetable oil. Add a few drops of food coloring to the water, using a different color for each group of students. Place a penny in the bottom of each bowl. Ask the students to walk away from the bowls and observe at which point the penny disappears from view. This is determined by the index of refraction of the liquid.
White light is a mixture of colors that move at different speeds. As white light passes through a prism, each color is bent at different angles, and the colors become visible. Demonstrate this to students by placing a glass prism on an overhead projector. The light from the projector should show up on the ceiling as a rainbow of colors. Students can also build their own prism by placing a mirror on the bottom of a tray filled with water and setting it in the sunlight.