Why are there rainbows? (continued)
  • The index of refraction is not completely independent of frequency 
  • Light of higher frequency is bent (or refracted) more than a lower frequency



    The raindrop and the light ray

    Finally, when light hits a surface with a different index of refraction, some light is reflected. 
    Dispersion in drop
  • 2 points of refraction, 1 point of reflection.
  • Light comes in from the left. 
  • At the first boundary, different colors head off in slightly different directions.
  • At the back surface (right), some light is reflected. 
  • Now when it comes out the front surface (left), the different colors are refracted again. (Since this surface is not parallel to the input surface, the two light rays shown come out at slightly different angles. This difference in angles gives rise to the rainbows we see.)
  • View of rainbow

    So here you are. You look up at one angle and see blue and another at angle and you see red. Now, if you've got some algebra background you can go to the next page