1. Refraction

2. Refraction is the bending of waves as they go from one medium into another
If the new medium is more dense, the wave will bend toward the normal in the 2nd material
If the new medium is less dense, the wave will bend away from the normal in the 2nd material

4. Refraction: Snell’s Law
Light changes direction when crossing a boundary from one medium to another. This is called refraction, and the angle the outgoing ray makes with the normal is called the angle of refraction.

5. Light waves slow down when they enter more dense materials
If a wave is not coming straight into the material, a part of the wave slows down first, while the rest continues at a fast pace
This changes the direction of the wave, causing the refraction

6. As the speed of the waves decreases, so does the wavelength
We saw this in the ripple tank
The following diagram shows the bending of the wave as it enters the 2nd, more dense, material and the waves are closer together

8. The refraction of light as it passes out of water is what causes us to think an object in the water is not where it really is . . .

9. Light reflects off the quarter and travels through the water until it reaches the surface
As it crosses the surface into the less dense air, it bends . . .

10. . . . Towards the normal in more dense materials, away from the normal in less dense materials

11. Therefore, we think the quarter is in a different location than it truly is

12. Refraction: Snell’s Law
Refraction is what makes objects half-submerged in water look odd.

13. When you see heat ripples above a hot grill or pavement on a very sunny day, this is also refraction
The material itself is not different, standard air in both cases
The difference in material this time is the density due to change in temperature
Hot air is less dense, so it causes the light to refract
This rippling effect is what causes a mirage image in the desert

14. Sound Refraction
Sound waves can also be bent by different temperatures of air
The sound waves get bent towards the colder air and away from the warmer air
This is why there are time when you can very clearly hear voices across a lake on one still day, and not on another still day
If the colder air is along the surface of the lake, the sound will be louder and carry farther