1. Refraction of Light Refraction and Lenses 2011-2012

2. Refraction The bending of a path of light. It occurs when one part of each wave is made to travel faster (or slower) than another part. Refraction occurs at the boundary between two media.

3. Wave Fronts Lines that are drawn to represent the positions of different crests. wavefronts

4. Index of Refraction The index of refraction of a material is a number that indicates how many times slower that a light wave will be in a medium than in a vacuum.

5. Index of Refraction, n MaterialIndex of Refraction Vacuum1.0000 Air1.0003 Ice1.31 Water1.333 Ethyl Alcohol1.36 Plexiglas1.51 Crown Glass1.52 Light Flint Glass1.58 Dense Flint Glass1.66 Zircon1.923 Diamond2.417 lowest optical density highest optical density

6. How Do We Use This? As the lawnmower hits the grass, it will slow down (more dense), causing it to bend towards the normal, then will speed up (less dense) as it leaves the grass, causing it to bend away from the normal. fast slow fast

7. Mnemonics FST = Fast to Slow, Towards the normal SFA = Slow to Fast, Away from the normal

8. Snell’s Law medium 1 medium 2 θ1θ1 θ2θ2

9. Atmospheric Refraction Mirage – the refraction of light in air. It is caused by a layer of hot air near the ground. The light travels faster through the hot air and produces a gradual bending of light rays. A similar situation occurs when a driver perceives the roadway to be wet when it is not.

10. Dispersion Dispersion – the separation of light into its individual wavelengths Prism Raindrop

11. Total Internal Reflection Total internal reflection – the light ray is completely reflected. When the light ray emitted no longer passes between the two boundaries, it is totally reflected. Critical angle – the angle beyond which light no longer refracts

12. Total Internal Reflection

13. Conditions for Total Internal Reflection 1.The light is in the more dense medium and approaching the less dense medium. 2.The angle of incidence is greater than the critical angle.

14. Optical Fibers The light is incident at an angle greater than the critical angle so that no energy is lost. All light is reflected within the medium.

15. Assignment Page 487, Problems 1-5 Light Refraction Worksheet