What the Prism Proved: teacher key

Rainbows, grade 9 edition, written for 9th grade. For centuries people argued about where rainbow colors come from. Follow Newton's two-prism test, the single ray that makes the bright arc, and the dark band between two bows.

Read the book. Print this page for the key.

Questions and answers

1. What did Newton's second prism show?
   • It added new colors
   • It brought the colors back together into white light (answer)
   • It made the light dimmer
2. What makes the bright arc of a rainbow?
   • Rays bunching up near the smallest angle of deviation (answer)
   • A cloud reflecting sunlight
   • Seven kinds of raindrops
3. Why is Alexander's band dark?
   • Almost no sunlight is scattered toward your eyes from there (answer)
   • A cloud blocks the sun
   • Violet light fills it
4. Why did the two-prism experiment help show the colors were already in sunlight?
   • Glass makes color, so two prisms make more
   • If a prism made color, a second prism could not turn the colors back into white (answer)
   • It proved Aristotle right
5. What does 'supernumerary' suggest about the extra arcs?
   • They are additional bows (answer)
   • They are the same as fogbows
   • They are red

Words

• spectrum: band of colors
• refraction: light bending
• supernumerary: extra, additional
• indigo: deep blue-violet