Why are danger signals red? In a light haze of very small particles, how many times more is green…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Why are danger signals red? In a light haze of very small particles, how many times more is green light () scattered than red light ()?
Need a reminder? The key ideaShow
Very small particles, such as air molecules, scatter light in proportion to : blue far more than red. Large particles, such as cloud drops, scatter all colours about equally, which looks white. The Tyndall effect is the path of a beam made visible by scattering.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Why red. Red has the longest wavelength we see, so fine particles scatter it least. A red light keeps its strength over a long distance, even in haze.
Step 2. Green against red. .
Answer: red is scattered least; green is scattered about times as much.
Check. A green light fades sooner in haze than a red one.
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