In my garden, when I'm watering the plants I sometimes see a rainbow or two. How did two rainbows appear? Why can't I see three rainbows then, or how can I see three rainbows?
[Physics] Double rainbows
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In my garden, when I'm watering the plants I sometimes see a rainbow or two. How did two rainbows appear? Why can't I see three rainbows then, or how can I see three rainbows?
Best Answer
The two rainbows that are formed are the primary and secondary rainbows respectively, in order of their intensity or brightness, as you may call it. A primary rainbow is formed as a result of a three- step process: Refraction with dispersion, followed by total internal reflection and then refraction.
The secondary rainbow is formed due to a four- step process: Refraction with dispersion, followed by total internal reflection(twice in this case) and refraction again.
Check out the following:
It is found that in case of the primary rainbow, violet light emerges at an angle of 40 degrees relative to the incoming light and red light at an angle of 42 degrees; thus we see the primary rainbow with red at top and violet at bottom.
In case of the secondary rainbow, emergent angles are 50 degrees and 53 degrees with respect to the incoming light, for red and violet colors respectively. Thus, the violet color is at the top while red is at the bottom.
The intensity of the light is reduced at the second internal reflection, and hence the secondary rainbow is very faint in the sky.You may take a look at the following:
A third rainbow even if it is formed as a consequence of successive total internal reflections, will be too dim to be visible.