1. Adv Physics
Chapter 22
Sections 3 and 4

2. Refraction Review
If i = 0, no refraction since all parts of the wave change speed at the same time
If i > 0 and travels into a slower medium the wave bends toward the normal
If i < 0 and travels into a faster medium the wave bends away from the normal

3. Apparent Depth
Consider a quarter at the bottom of a cup filled with water
As light from quarter leaves the water it bends away from the normal
Person believes light came from a quarter much closer to the surface than it really is

4. Apparent Depth Depth an object appears to have due to refraction
Only time you will see the object in its true location is if you look straight down along the normal

5. Today’s Warm Up
Light travels from diamond (n=2.42) into air with an angle of incidence of 45˚.
What will happen to the speed of light?
Will the light bend toward the normal or away from the normal?
What is the angle of refraction?
What does this mean?!?!?!?!?

6. Total Internal Reflection

7. Total Internal Reflection

8. Total Internal Reflection
When reflection occurs at a boundary going from more to less dense
r Air water i
As i increases, r increases until eventually r = 90 degrees

9. Critical Angle
Angle of incidence that causes light to bend along the boundary with an angle of refraction of 90 degrees
Neither refracted or reflected

10. Example What is the critical angle for water? n1sinΘ1 = n2sinΘ2
1.333 sinΘ1 = 1 sin90
1.333 sinΘ1 = 1
sinΘ1 = 0.750
Θ1 = 48.6 degrees

11. Sample Problem
What is the critical angle for glass of index 1.5? For diamond with an index of 2.419?
41.8
24.4

12. Diamond
Diamond has a really high index of refraction and a really low critical angle
Light trying to leave the diamond gets internally reflected multiple times
This makes diamond sparkle

13. Practice
What is the critical angle for zircon whose index of refraction is 1.923?

14. Practice
A swimmer under the water shines a flashlight up at the surface. At what minimum angle, made with the normal to the interface, will the beam be completely reflected back into the water? The index of refraction for water is 1.33.

15. Practice
Using a block of a transparent, unknown material, it is found that a beam of light inside the material is totally internally reflected at the air-block interface at an angle of 48˚. What is the index of refraction?

16. Last Question
Is it possible for their to be total internal reflection when light travels from air to water?