Between the primary and secondary rainbows, there is a dark band known as Alexander's dark band. This is because

Options

A. light scattered into this region interfers destructively.
B. there is no light scattered into this region.
C. light is absorbed in this region.
D. angle made at the eye by the scattered rays with respect to the incident light of the sun lies between approximately `42^(@) and 50^(@)`.

Answer

A, D

Explanation

This dark band is present because light scattered into this region has interfered destructively. The reflected rays in this region do not reach the observer.
As discussed in Q. 9.4, the primary rainbow is formed when we looked in the direction opposite to the Sun at an angle of `42^(@)`. The secondary rainbow is observed at `50^(@)`. Between the axis of primary and secondary rainbows, there is no reflection back of light rays to the eyes of the observer. So, a dark band is present between them. The correct options are (a) and (d).