One Arc, Four Theories of Light: teacher key

Rainbows, grade 12 edition, written for 12th grade and up. The rainbow is a bright fold in the paths of light rays. Follow its geometry, the Persian and German globes, Newton's prisms, Young's waves and the exact theory of Mie and Airy.

Read the book. Print this page for the key.

Questions and answers

1. Why is the sky between the two bows of a double rainbow dark?
   • A cloud blocks the sun there
   • Almost no sunlight is scattered toward your eyes from that part of the sky (answer)
   • Violet light fills that part of the sky
2. Who worked out the exact solution for light scattered by a sphere in 1908?
   • Gustav Mie (answer)
   • Thomas Young
   • David Brewster
3. Why do physicists still use Airy theory when Mie's exact solution exists?
   • Airy theory is newer
   • Mie's solution ignores spheres
   • Mie's solution is an infinite series that converges slowly (answer)
4. Under what condition do extra pastel bands show best?
   • When raindrops are large and uneven
   • When raindrops are small and nearly the same size (answer)
   • When the sun is very high
5. In this passage, what does 'polarized' tell you about rainbow light?
   • It has no color
   • It travels slowly
   • Its waves are strongly aligned in one way (answer)

Words

• antisolar: opposite the sun
• dispersion: spreading by wavelength
• interference: waves adding together
• polarized: light waves aligned