1. Refraction Principles of Physics

2. Refraction • Change in direction of light as it moves into a new medium and speed changes • Only occurs if light enters medium such that 0˚< θi< 90˚ θr = angle of refraction θi θr

3. Refraction can only occur when: • there is a medium change • the light enters at an angle between 0˚ and 90˚ • When a toy car goes from tile to carpet such that both front wheels hit the carpet at the same time, the whole car slows down at the same time. A change in direction does not occur. • When a toy car goes from tile to carpet at an angle. Each wheel hits the carpet at a different time. The first wheel to hit the carpet, slows down before the others causing the car to turn toward it.

4. Measuring Angles To measure the angle place the protractor on the normal line facing the ray Measure the angle from the normal line to that ray θi 90˚

5. Measuring Angles To measure the angle place the protractor on the normal line facing the ray Measure the angle from the normal line to that ray 90˚ θr

6. Measuring Angles Determine the incident and refracted angles

7. Measuring Angles Determine the incident and refracted angles

8. Measuring Angles Determine the incident and refracted angles

9. Index of Refraction • Ratio of the speed of light in a vacuum to the speed of light in other materials n= index of refraction (unitless) c = speed of light in a vacuum v = speed of light in material Greater n →more the light slows down in the material

10. Example Determine the speed of light in water if the index of refraction for water is 1.33

11. Snell’s Law • Relates the index of refraction to the angle of refraction Don’t forget ˚ is a unit!!!

12. Indices of Refraction

13. Example Determine the angle of refraction. n1 = nair= 1.00 n2 = nglass= 1.52 θi= 30˚ θ2 ≈ 19˚ crown glass θr

14. Critical Angle θc = critical angle: incident angle that causes refracted angle to be 90˚ in air

15. Total Internal Reflection Transparent materials can reflect. Total Internal Reflection: nhighto nlow θi > θc i i i θi= θr

16. Dispersion • All wavelengths of light travel at 3x108 m/s in a vacuum • In other materials each wavelength travels at a different speed • In most materials red travels fastest and violet travels slowest • Red is refracted least and violet is refracted most therefore the colors separate