Question

Why is it that rainbows always show up with red on the outside of the arc and blue on the inside? Can you have a rainbow with its colors reversed?

Answer 1

Ans.

• Oftenly, a rainbow seems like a circular arc in the sky.
• From the ground only a half circle of color is oberved with red being the color visible at the outer side and blue is the color of inner side.
• Formtion of circle (or half-circle) occurs because of the presence of a collection of suspened droplets in the environment .
• These droplets can concentrate the dispersed light at an angles of deviation of approx. 40-42 degrees with respect to the original light path from the sun.
• In general, a circular arc is formed by these droplets and every droplets inside the arc disperse light and reflect it back to the observer.
• Within the arc, each droplet refrect and disperse the entire spectrum of visible lights.
• Refraction of red light out of a droplet happens at a steeper angles then the blue light relative to ground.
• Thus, upon observation at a steeper angle with respect to ground, red light is refrected to the eyes of observer by these water droplets within this line of sight.
• Refrection of blue light happens at a less steeper angle and is moved along a trajectory passing over the head of observer.
• Thus, red light is visible at the top upon looking at a steeper angle while looking at a less steep angle showes blue light on the bottom.
• This is why, in a rainbow, at the top and on the outer side of rainbow red color is seen where as blue color is observed on the bottom and the inner side of rainbow.
• Occurance of secondary rainbow is a rare instance where colors appear in the reverse order.
• Secondary rainbow is formed when reflection of light occurs twice inside the raindrop.
• Since, second reflection is seen upside down, so that is why colors are reversed in the secondary rainbow.