Question

Fill in the blanks:
Rainbows are caused by the dispersion of white light in ______
(A) raindrops
(B) prism
(C) glass slab
(D) air

Answer 1

Hint
Rainbows are caused by the reflection, refraction or the diffraction of white light on the water droplets. This causes the white light to break up into a spectrum of light that appears in the sky as the rainbow.

Complete step by step answer
A rainbow is a meteorological phenomenon. The white light consists of lights of various wavelengths and they together appear as white light as the speed of lights of all wavelengths is the same in air. When it is raining, the white light may move through these water droplets from the rain. Some of the white light gets reflected from the outer surface of the drop but the rest of the light enters the water drop.
Now since the refractive index of water is different from air, so the speed of lights of various wavelengths is different in water. So the white light gets split up into its constituent colours. These split up wavelengths consist of the colours that we see in a rainbow.
So the rainbow is caused due to the dispersion of white light in the raindrops.
So option A is correct.

Note
When the white light passes through the water drop, it gets split up into the constituent colours. This is because the speed of different wavelengths of lights is different in any medium other than air. As a result, the amount of deviation is different for lights of different wavelengths. Sometimes a double rainbow is seen outside the primary arc. This happens when the light gets reflected twice before leaving the water droplet.