Newton turned a second prism upside down and got white light back…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Newton turned a second prism upside down and got white light back. What happens instead if the second prism is placed the same way up as the first, so that both turn the light the same way?
Need a reminder? The key ideaShow
White light is a mixture of colours. Glass has a slightly larger refractive index for violet than for red, so violet is slowest and bent most: a prism spreads white light into a spectrum, red to violet.
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. The first prism spreads white light into a spectrum.
Step 2. The second prism, the same way up, bends every colour further in the same direction, violet again more than red.
Step 3. The result. The deviation is about doubled, and the spectrum is spread wider. No white light comes back.
Answer: a wider spectrum, turned through about twice the angle.
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