Rainbow Challenge - What cause prism to form a rainbow? ✏ Solution: The refractive index of many materials (such as glass) varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow! Watch full video: https://www.youtube.com/watch?v=9KcU6NfR8Og