(a) Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.

(b) A star appears slightly higher (above) than its actual position in the sky. Illustrate it with the help of a labelled diagram.

(a) When a beam of white light is allowed to pass through a prism, due to phenomenon of dispersion, it gets splits into seven colors. This is known as spectrum of white light. Since the angle of refraction is different for different components of white light due to which the colors of the light are refracted at different angles and thus results in formation of the spectrum.

The ray diagram to illustrate the dispersion of white light when it passes through a glass prism is as follows:

(b) The light rays coming from the star travels through different layers of atmosphere and due to varying optical density, there is bending of light continuously. Due to phenomenon of atmospheric rarefaction, this bending of light results in curved path of light rays. It seems to the observer that the light is coming straight from source and that’s why the stars appears higher than the actual position of them.