The skeptical, inquiring mind feels that the explanations aren't complete. Does this explain anything? After entering the water drop, the light rays reflect once, then refract out of the drop. But, considering that a given color strikes the water surface the second time at the same angle of incidence that it did the first time, why does the diagram show only reflection the first time and only refraction the second time? If this is total internal reflection, why doesn't the light keep reflecting every time it reaches the drop's surface, endlessly, without ever emerging?
If this is not total internal reflection at the first surface, then shouldn't some light emerge there, and wouldn't that cause a rainbow seen when looking toward the sun?
Inquiring minds want to know. A perfect rainbow. Dorset, UK. Southern Scenic Photography. The rainbows we see are not formed by light from a single drop of water, but by light from a whole cloud of water drops, emerging in many directions.
We see only that light that happens to be directed toward our eyes. The droplets that direct a rainbow's red light to our eyes are not the same ones directing blue light to our eyes. Total internal reflection plays no role in this, and the reason is interesting. If light impinges into the drop at such an angle that some of it refracts into the drop, then, if reversed, light must also pass out of the drop along the same path.
Due to the spherical shape of the water drop, any ray passing internally along a chord makes the same angle to the normal at each surface. So any ray entering the drop cannot subsequently ever impinge on the surface at an angle where there's total internal reflection. The light inside a water drop does continue to reflect internally several times and each time some of it also refracts out of the drop. Some light does refract out of the drop at the point of first internal reflection.
So why doesn't it also produce a rainbow seen when looking toward the sun into a cloud of water droplets—as a large arc centered on the sun? Such colorful arcs, called parhelia, are often seen, but these are due to ice crystals in the atmosphere, not to water droplets. Some people call them "rainbows".
Sometimes you see a double rainbow -- a sharp rainbow with a fainter rainbow on top of it. The fainter rainbow is produced in the same way as the sharper rainbow, but instead of the light reflecting once inside the raindrop, it's reflected twice.
As a result of this double reflection, the light exits the raindrop at a different angle, so we see it higher up. If you look carefully, you'll see that the colors in the second rainbow are in the reverse order of the primary rainbow.
And that's really all there is to rainbows. Light and water happen to combine in just the right way to paint a beautiful natural picture. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Prev NEXT. Even though rain drops are different from glass prisms, they have a similar effect on travelling sunlight.
For light to break out into its different colors that forms it, a change in medium has to occur; therefore when it rains, light travels through air to travelling through water droplets. This forces the different colors in the light to react differently, each refracting and dispersing at a different speed and angle, forming the seven colors in rainbows: red, orange, yellow, green, blue, indigo and violet.
The light once refracted within the water droplet, is then reflected at the other surface of the droplet, and then dispersed. To witness a rainbow, the Sun has to be behind you, and the light has to travel through raindrops in order to form the famous colorful arch. However, if it were not for the ground a rainbow would actually form as a circle.
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