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Why is the sky blue, and why does the same sky turn red at sunset? Why does a wet-looking patch appear on a hot road and retreat as you drive towards it? Why do stars twinkle when planets do not, and why is every danger signal in the world red?
These look like six unrelated facts to memorise. They are six consequences of two ideas.
Idea one: white light is not one thing. It is a bundle of wavelengths, and a glass prism separates them because each colour bends by a different amount.
Idea two: when light meets particles far smaller than its own wavelength, the short wavelengths are thrown sideways much more strongly than the long ones. Blue scatters; red carries on.
Every question in this topic is one of those two ideas dressed as a real-world observation. Once you can say which of the two is at work, you can reason the answer out even for an example you have never seen before.
1. The sky appears blue mainly because:
2. When white light passes through a glass prism, which colour is deviated the most?
3. The sun appears reddish at sunrise and sunset because:
4. To an astronaut in space, the sky appears:
5. A rainbow is formed in the sky by which combination of effects inside water droplets?
6. Red is used for danger signals and traffic stop lights because red light:
7. The Tyndall effect refers to the:
8. The mirage seen on a hot road on a summer afternoon is caused mainly by: