How Rainbows Form | Summary and Q&A

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December 27, 2014
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Physics Girl
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How Rainbows Form

TL;DR

Rainbows form due to refraction and dispersion of light, with different colors bending at different angles. The brightness of each color at its maximum angle creates the distinct appearance of a rainbow.

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Key Insights

  • 🙂 Rainbows form due to the bending of light through refraction and the separation of colors through dispersion.
  • 🌈 The brightness of each color at its maximum angle determines its appearance in the rainbow.
  • 🙂 The sky appears darker above a rainbow because none of the light can make it out above the red color.

Transcript

Surely you've seen a rainbow. Maybe you were chasing tornadoes and happened upon one. But did you ever notice that the sky is darker above a rainbow than below? I never did until someone pointed it out. We're going to find out why this is so with the help of refraction of light, dispersion, and the incomplete story you're usually told about why rai... Read More

Questions & Answers

Q: Why is the sky darker above a rainbow than below?

The sky is darker above a rainbow because none of the light can make it out above the red color, making the sky appear darker. Below the violet color, all colors mix again and form white, making the sky appear lighter.

Q: How does refraction and dispersion create the colors in a rainbow?

When white light enters a droplet of water, it refracts and separates into a spectrum of colors through dispersion. Different colors bend at different angles due to their varying speeds in water, creating the colors in a rainbow.

Q: How does the brightness of each color contribute to the appearance of a rainbow?

At the maximum angle of refraction, each color reaches its maximum brightness. This causes the colors to stand out against each other, with violet being the brightest due to its larger maximum angle. The mixture of colors below the maximum angles appears white.

Q: Why is there a second rainbow, and why are the colors flipped in order?

The second rainbow is caused by a double reflection of light inside the droplet, resulting in a different order of colors. The sky above the second rainbow appears lighter because the light had to enter the droplet from below the midpoint.

Summary & Key Takeaways

  • Rainbows are formed through refraction, which is the bending of light as it moves from one medium to another, such as from air to water.

  • When light enters water, it slows down and different colors bend at different angles due to different speeds.

  • This dispersion of white light creates a spectrum of colors. The brightness of each color at its maximum angle determines the appearance of a rainbow.

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