Which optical phenomenon is responsible for the early sunrise and delayed sunset?

Dispersion of white light occurs because every colour travels with a different speed in a transparent medium.

$A$ prism $ABC,$ with base $BC,$ is placed in four different orientations as shown. $A$ narrow beam of white light is incident on the prism as shown. In which of the following cases,after dispersion,the third colour from the top corresponds to the colour of the sky?

$(i)$ Write the range of distance for a person having normal vision.
$(ii)$ $A$ person needs to use glasses for reading a newspaper. Identify the defect in his vision and the type of lens he would need to correct it.
$(iii)$ Sometimes when we enter into a dark room from bright sunlight,we are unable to see objects clearly. Why?

In the dispersion of white light by a prism,which color of light has the maximum velocity?

$A$ man wearing glasses of focal length $+1\, m$ cannot see objects beyond $1\, m$. What is the defect in his eye?