Question

Pick the wrong answer in the context with rainbow.
A. when the light rays undergo two internal reflections in a water drop, a secondary rainbow is formed
B. the order of colours is reversed in the secondary rainbow.
C. an observer can see a rainbow when his front is towards the sun.
D. rainbow is a combined effect of dispersion refraction and reflection of sunlight.

Answer 1

Hint: Rainbow is a phenomenon caused by refraction, reflection and dispersion of light in water droplets which gives a wide bandwidth of light that appears in the sky. It appears to be a multicoloured arc.

Complete step by step answer:
To view a rainbow, a person’s back must be towards the sun and look into the atmosphere region about 40 degree above the ground with droplets of water or even a light mist. Every droplet of water acts as a prism which disperses and reflects the light back into the eyes. The rainbow is viewed with red colour being perceived at the top of the bow because red light is refracted out of a droplet at steeper angles towards the ground when compared to blue light. A rainbow forms a spectrum of lights consisting Violet, Indigo, Blue, Green, Yellow, Orange and Red. A rainbow actually forms a full circle but the observer from the ground can view only a half circle because the bottom half of the arc is prevented by ground which means the suspended water droplets are not present below the ground region. Bright sunlight, suspended water droplets and proper sighting angle are the three important features for viewing a rainbow.
Therefore, the correct option for the given question is option (C).

Note: An observer cannot view a rainbow when his front is towards the sun because light is refracted in many ways from droplets between the sun and observer. This can only happen when the sun is behind the observer and refracted back or else the sun’s brightness makes it too hard to see.