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

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

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

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

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

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?

Another Round of T.I.R.!

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

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.

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?

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

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

Polarization

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