(a) The angle between incident ray, produced forward and emergent ray, produced backward is called angle of deviation D. (b) The splitting up of white light into its constituent colours on passing through a refracting medium like a glass prism is called dispersion of light. The dispersion of white light occurs because different colours of light bend through different angles with respect to the incident ray, as they travel with different speeds in a prism. The red light bends the least while the violet light the most as shown below(c) The given diagram shows the formation of rainbow in the sky.