1. Refraction Chapter 12 (p. 511-545)

2. Refraction Refraction: The bending or change in direction of light when it travels at an angle from one medium into another medium. Occurs at the boundary of the 2 materials Light travels at different speeds through different mediums –Ex. Speed of light in a vacuum is 3.00 x 10 8 m/s Speed of light in water is 2.26 x 10 8 m/s Speed of light in acrylic is 1.76 x 10 8 m/s Its speed depends on the density of the medium As light travels from one medium to the next it’s speed and direction change.

3. normal R i r

4. Fermat’s Principle When light travels from one point to another it follows the path that will take the least time. In a single medium this is a straight line Light bends when changing mediums so that it travels for a greater distance in the faster medium. air water

5. Three Laws of Refraction: 1. Light that travels at an angle from a less dense medium (where its speed is faster) into a more dense medium (where its speed is slower) will have a refracted ray that bends towards the normal

6. Faster into slower medium = bends towards normal

7. Three Laws of Refraction: 2. Light that travels from a more dense medium (where its speed is slower) into a less dense medium (where its speed is faster) will have a refracted ray that bends away from the normal

8. Slower into faster medium = bends away from normal

9. Three Laws of Refraction: 3. Light that moves straight on from one medium to another medium does not bend. It is not refracted.

10. Index of Refraction n = c /v Refractive Index: Ratio of the speed of light in a vacuum to the speed of light in a given medium n is the index of refraction c is the speed of light in a vacuum (3.00 X 10 8 m/s) v is the speed of light in a medium (m/s) Can also be written: n = sin of angle of incidence sin of angle of Refraction ** See p.524 for chart of n for various substances**

11. Index of Refraction E.g. Index of refraction of water: n water = c v speed of light in a vacuum speed of light in water = 3.00 X 108 m/s 2.26 X 108 m/s = 1.33

12. Practice Problems! To Do: Complete Refraction wksht Pg 519 #1-3, p.525 #1-3, 6 c vn Hints! n = c/v c = nv v = c/n Check: v is always less than c