1. Dispersion, Rainbows, Mirages, Polarization
Optics and Refraction
Dispersion, Rainbows, Mirages, Polarization

2. Dispersion
Different frequencies actually have different indices of refraction, moving through the medium at different speeds
Red light bends least; violet most
White light refracting through a prism will split into its component colors

3. Rainbows
The rainbow is caused by a whole set of circular prisms (raindrops) illuminated from behind
It is a characteristic phenomenon of total internal reflection occurring in many raindrops at once

4. Total Internal Reflection
Light that passes through the raindrop continues on, invisible to our eyes
Light that undergoes T.I.R. is reflected back to us
Dispersion—the difference in speed between colors of light—and Snell’s Law cause the red light to emerge from the sphere at a 42° angle from the original light
Similarly, violet emerges at 40 °angle

5. The Result of T.I.R.…
The observer sees red light from the upper drops (42°) and violet light from the lower drops (40°)
Between 42° and 40°, the other colors appear
At angles less than 40°, where T.I.R. is not visible, the colors mix about equally

6. Causing a Lovely Rainbow…
…illuminated within by all the light that did not undergo one round of total internal reflection. See how the rainbow’s interior is always brighter than the surrounding sky?
What is causing the secondary bow, do you think?

7. Another Round of T.I.R.!

8. Did you Know that rainbows are actually circular?
…so why do they look like bows?

9. And the same effect can be caused with ice crystals?
It’s called “pilot’s glory” or “Buddha’s light,” and is seen by pilots in clouds.

10. Mirages: Another effect of refraction
From your standpoint, you can see puddles of “water” on the ground
When you arrive at the location, no water is present!
Why not?

11. Light Appears to Emanate from the Ground…
…causing an image to appear at ground level where no image truly exists.

12. A tree on the ground??? Can't be!
…it must be a puddle of water reflecting the tree’s image, right? Right?

13. Polarization

14. Glare-reducing sunglasses
Uses of Polarization
Glare-reducing sunglasses
LCD