1. 4.6 Refraction

2. Penny Demo

3. Magic?

5. Refraction Bending of light as it passes from one medium into another
Why?
The speed of light is:
3.00 x 108 m/s in a vacuum
2.26 x 108 m/s in water
1.76 x 108 m/s in acrylic

6. Rules Light bends TOWARDS to normal when the speed decreases
Light bends AWAY from normal when the speed increases (up up and away!)

7. incident ray
MEDIUM #1
MEDIUM #2

8. incident ray
MEDIUM #1
MEDIUM #2

9. incident ray
MEDIUM #1
MEDIUM #2

10. Sample Question
If I had a beam of light passing from a water medium to an acrylic medium, would the light bend towards or away from the normal?

11. Sample Question
If I had a beam of light passing from a water medium to an acrylic medium, would the light bend towards or away from the normal?

12. Angle of Refraction The angle between the refracted ray and the normal
(Add this to your diagram)

13. Partial Reflection and Refraction
Some light that hits a surface refracts into the new medium
Some of the light is reflected back into the same medium
Ex. two way mirrors and mirrored sunglasses

15. Total Internal Reflection

16. Critical Angle
Angle of incidence increases causing angle of refraction to reach up to 90º.
critical angle: the angle of incidence that produces a refracted angle of 90º

17. Total Internal Reflection
total internal reflection: angles greater than the critical angle causing incident ray to be reflected back into same medium
DEMO

18. Summary: Two conditions for total internal reflection:
Light must be travelling slower in the first medium compared to the second
The angle of incidence must be large enough that no refraction occurs in the second medium

19. Applications:
Diamonds: very high n, therefore very small critical angle, therefore lots of total internal reflection = sparkle
Fiber Optics: light travels along glass cable

20. Triangular prisms: used in optical devices such as cameras and binoculars since they do not deteriorate like the reflective film in mirrors.

21. Retro reflectors: cut off from corner of cube- used to send light back parallel to incident light. Use on moon, bike reflectors and road signs.