1. EFFECTS OF REFRACTION

2. Dispersion of White Light
White light separates into its color spectrum through a triangular glass prism-> called dispersion
Each color of white light is slowed down by glass differently with:
Violet light slowed down the most and bends most away from the normal
Red light slowed down the least and bends most towards the normal compared to the rest of the colors
Note: all colors bend away from normal as light speeds up; it’s just that red light bends more towards the normal with respect to violet

3. Rainbow and formation of rainbow
white light
This droplet is perfectly positioned to reflect only RED into the eye
In between these droplets are thousands more, each droplet reflects just one colour into the eye, resulting in the rainbow swath seen by the observer.
42º
TIR
white light
TIR
40º
TIR
observer
TIR
This droplet is perfectly positioned to reflect only VIOLET into the eye

4. Formation of Rainbows Invisible
Since all the droplets at a certain angle form the observer are responsible for a certain colour being seen (e.g., 42º for red and 40º for violet), the rainbow is seen as an arc.
if the ground were not in the way, it would be a perfect circle.
Invisible

5. But you might find these
One can never “catch up” to a rainbow because:
Moving towards a rainbow means that the droplets responsible for the rainbow are now at the wrong angles to the observer to produce the rainbow, BUT a new set of droplets just behind the original set are at the right angles.
Plus, there is NO pot of gold at either end of the rainbow.
But you might find these

6. Apparent Depth
The fish appears closer to the surface than it really is when viewed from top

7. APPARENT DEPTH Apparent depth
eye
air
water
real meter stick
eye
air
water
real meter stick
apparent meter stick
Apparent depth
= the depth an object appears to be at due to refraction of light

8. APPARENT DEPTH
eye
air
water
real meter stick
apparent meter stick
Objects in water appear to be closer to the surface than they really are
Because light refracts away from the normal at it enters air from water
eye
air
water
real meter stick
apparent meter stick

9. Flattened Sun observer
Refracted rays bend towards the normal as light slows down
Earth
observer
atmosphere
real sun
apparent sun
light refracts at the vacuum-atmosphere boundary
(denser near Earth’s surface)
Sun appears flattened at sunset due to 2 reasons:
1. Light from bottom of the sun bends the most as it’s closer to Earth’s surface where the atmosphere is denser
2. Light from bottom of the sun enter the atmosphere with greater angle of incidence therefore has larger refracted angle
Correction for Figure 5 p 536 of textbook: Light travels through the atmosphere should be CURVED because the atm is gradually more dense near Earth’s surface causing an infinite number of very small refractions occurs (which make the light ray curved rather than straight)

10. MIRAGE
- Air of different temperatures has different refractive indexes, just like many different mediums.
- The closer the air is to the ground, the hotter it will be, and the smaller its refractive index (i.e. light speeds up going towards the hotter air layer)
Light speeds up, away from normal
Light slows down, towards normal
(highest n)
(lowest n)
Our brain interprets a inverted virtual image coming from the ground
TIR occurs as i> Ɵc

11. MIRAGE
- Light speeds up as it travels through successive layers of warmer air each with a lower n; it thus bends away from normal. The incidence angles also get larger
Eventually, this incidence angle will be greater than Ɵc. TIR occurs and light is reflected upwards towards the observer.
- As light slows down as it moves from hot (low n) to cool air (high n); it thus curves towards the normal and reach the eye of the observer eventually
- Our brain conditions us to think there is an inverted virtual image coming from the ground and gives us the illusion of a “puddle of water” on the road that we cannot seem to reach ever.