Below is an excerpt from a Communication and Literacy Skills practice test of the Massachusetts Tests for Educator Licensure.
Read the passage below; then answer the six questions that follow.
1. Does a rainbow point the way to a pot of buried gold, as claimed in popular folklore? Or is it the multicolored serpent some people in Asia, Australia, and Brazil see streaking across the sky? Others see a rainbow as a heavenly bridge connecting this world and the world beyond. Among Arabs and some Bantu in central Africa, it is the bow for God’s arrow; to early Christians, it was the throne of Christ; and among the Nandi, Masai, and California Yuki, it is the robe of God. To twenty-first-century scientists, it is something quite different. For them, the band of soft colors that arcs across the sky simply shows the spectrum of the colors in sunlight spread out by raindrops.
2. How does it happen? Perhaps the best place to begin is by understanding that sunlight is white light. Although white light contains colors, they are blended together; no color is visible until the light strikes an object. When that occurs, the object struck reflects one or more colors in the light while absorbing or refracting the others. The reflected light is the color the object appears to be when viewed with the human eye. Whereas solid objects send unabsorbed colors back to the eye, transparent objects such as glass or water bend the light as it passes through them. This bending is called refraction. A rainbow is caused by drops of water that both refract and reflect the light rays that enter them.
3. Of the two processes, refraction plays a particularly important role in the formation of rainbows. When light is refracted, each color is bent at a slightly different angle. As a result, the colors in the light separate, and it is then that the eye sees the spectrum of light we call a rainbow. In the spectrum, red light bends the least and violet light bends the most. Orange, yellow, green, and blue—always in that order—range between them. Hence, a rainbow is red along the top and violet on the inner side of the arc. In every rainbow, whether caused by sunlight striking raindrops high in the sky or water dripping from a garden hose in the backyard, the colors appear in the same order.
4. Rainbows appear only when the viewer is between the sun and the moist air. They are, therefore, most often seen early or late in the day, when the sun is low and there is rain in the area of the sky toward which the sun is shining. Each point on a rainbow is caused by the interaction of sunlight with a different drop of water. Sometimes only a short length of color is visible, which means that no drops of water are in adjacent areas of the sky.
5. As to the pot of gold, even if such a treasure were buried at the end of a rainbow, it could never be found. Any effort to discover this treasure is doomed to failure: whenever a viewer moves underneath the drops that form a rainbow, it disappears. Rainbows exist only when the positions of the light rays, the raindrops, and the observer align in the proper angles. When the angles change, the spectrum of visible colors vanishes.