Question

A rainbow has circular shape because:
A. The earth is spherical
B. Raindrops are spherical
C. The sun is spherical
D. None of these

Answer 1

Hint-
Rainbow is formed due to refraction of rays in water droplets
A ray of light entering a spherical water droplet will undergo refraction twice and the ray which is coming out of the droplet will be dispersed into the seven component colors of white light.

Complete step-by-step answer:
Rainbow is formed due to refraction of rays in water droplets. A ray of light entering a spherical water droplet will undergo refraction twice and the ray which is coming out of the droplet will be dispersed into the seven component colors of white light. The water droplets act like a prism.
The rainbow that is formed is actually a full circle but we are able to see only an arc because the horizon cuts off the lower half so we are not able to see the full circle. if we are high enough then we would be able to see the complete circle of rainbow.
The reason why rainbows appear to be curved is because of the angle at which the raindrops reflect the light. Usually the angle at which the sunlight is reflected from a droplet is about 42 degrees.

So, we can say that it is actually due to the spherical shape of the raindrops that the rainbows have a circular shape.

Note: The rainbow that is formed is actually a full circle but we are able to see only an arc because the horizon cuts off the lower half. The reason for the circular shape is the spherical shape of the droplets which reflect light at an angle making a cone of light.