1. Refraction

2. Refraction
Refraction – the change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds
Wave Fronts – lines that represent the position of different crests
At each point along a wave front, the wave is moving perpendicular to the wave front
The direction of motion is best represented by a ray

3. Refraction

4. Refraction of Sound
Sound waves are refracted when parts of a wave front travel at different speeds
This happens in uneven winds or temperatures
Sound waves tend to bend away from warm ground, since it travels faster in warmer air
On a cold night, the speed of sound is slower near the ground than above, so we can hear over larger distances

5. Refraction of Sound

6. Refraction of Light
A pond or swimming pool may appear shallower than it actually is.

7. Refraction of Light
A pencil in a glass of water will appear bent

8. Refraction of Light
An object can appear in a completely different place when perceived through two different media.

9. Refraction of Light
The air above a hot road seems to be moving due to the difference in densities of hotter and cooler air.

10. Refraction of Light
All of these effects are caused by changes in the speed of light as it passes from one medium to another, or through varying temperatures and densities of the same medium – which changes the directions of light rays

11. Refraction of Light

12. Atmospheric Refraction
On hot days there may be a layer of very hot air in contact with the ground, the light will travel faster through this air and will bend, creating a mirage
When you watch the sun set, you can still see the sun for several minutes after it has sunk below the horizon, because light is refracted by Earth’s atmosphere

13. Dispersion in a Prism
Light of frequencies closer to the natural frequency of the electron oscillators in a medium travels more slowly in the medium
Since different frequencies of light travel at different speeds in transparent materials, they will refract differently and bend at different angles
When light is bent twice at nonparallel boundaries, as in a prism, the seperation of the different colors is apparent
Dispersion – the separation of light into colors arranged according to their frequency

14. Dispersion in a Prism

15. Dispersion in a Prism

16. The Rainbow
The rainbow takes the concept of dispersion and multiples it through the atmosphere
The sun shines on water droplets in a cloud or when it is raining
The light is dispersed
by the raindrop into
its spectral colors

17. The Rainbow

18. Total Internal Reflection
Critical Angle – the minimum angle of incidence for which a light ray is totally reflected within a medium
Total Internal Reflection – the 100% reflection of light that strikes the boundary between two media at an angle greater than the critical angle
Optical fibers utilize the concept of total internal reflection to feed light from one location to another, these cables are very useful for communications

19. Total Internal Reflection

20. Index of Refraction (n)

21. Snell’s Law Snell’s Law: n1 sin θ1 = n2 sin θ2
(where n1 and n2 are the indices of refraction of the media on either side of the boundary, and θ1 and θ2 are the respective angles of incidence and refraction)

22. Practice Problem 1
Light travels from air (n=1.00) into water (n=1.33). If the angle of refraction is 30.0o, what is the angle of incidence?

23. Practice Problem 2
A ray of light in air (n=1.00) strikes a block of quartz at an angle of incidence of 30o. The angle of refraction of refraction is 20o. What is the index of refraction of the quartz?