Question 371
MediumOriginal questionSunlight looks white, but it is really a mixture of all the colours of the rainbow, as anyone who has seen light pass through a knows. Light travels in waves, and the colours differ in the length of their waves: red light travels in long, lazy waves, while blue light travels in short, ones.
Light goes in a straight line unless something gets in its way. It may be , as by a mirror; bent, as by a prism; or , sent off in all directions. When sunlight enters the Earth's atmosphere, it meets the tiny of the gases that make up the air, and these scatter it. Blue light, with its shorter waves, is scattered far more than the other colours. So when you look at any part of the sky away from the Sun, what reaches your eyes is mostly this scattered blue light.
Near the , the sky looks paler, almost white. Light arriving from low in the sky has passed through much more air, and has been scattered again and again until the colours are mixed together once more.
The same idea explains a red sunset. When the Sun is low, its light has to cross a great thickness of air to reach you. By then, most of the blue has been scattered away, and the reds and yellows are left to come straight through.
What is the passage mainly about?
Show the answer and explanation
Correct answer: D
Explanation
The passage explains that blue light is scattered most, and then uses the same idea to explain the blue sky, the paler horizon and the red sunset.
Scattering is the one idea that ties every paragraph together.
Worth noting
The prism and the mirror are examples used on the way; they are not what the passage is about.
- Concept
- Finding the idea that connects every paragraph
- Typical timeTypical
- 50 s
- Your timeYours
- —
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