Question

A passenger in an aeroplane shall
A) Never see a rainbow
B) May see a primary and a secondary rainbow as concentric circles.
C) May see a primary and a secondary rainbow as concentric arcs.
D) Shall never see a secondary rainbow.

Answer 1

Hint: Recall that the total internal reflection is the phenomenon in which the light rays will travel from a more optically denser medium to a less optically denser medium. This phenomenon occurs when the light rays get refracted at the point where the two mediums having different refractive index are separated.

Complete solution:
The passenger in an aeroplane shall see the primary and the secondary rainbow in the form of concentric circles. This is because the rays of light will undergo the phenomenon of total internal reflection from the secondary droplets also. When the light rays will pass from water to air then it gets refracted. When the angle of incidence in water reaches a certain value such that it will no longer refract but gets reflected, this angle is known as critical angle.
Also since the passenger is in aeroplane and also there is no ground ahead of him, so the passenger will see the rainbow as concentric circles.

Option B is the right answer.

Note: It is important to remember that the value of the angle of incidence is greater than that of the critical angle. The critical angle is the smallest angle of incidence that is responsible for the phenomenon of total internal reflection. Also the phenomenon of total internal reflection can take place only if the angle of incidence is greater than the critical angle. In this phenomenon, the speed of light changes as it travels from rarer to denser medium and vice versa.