1. Or I’m Bending Over Backwards for You
Refraction
Or I’m Bending Over Backwards for You

2. An Experiment

3. When a wave hits a boundary…
If it is at the natural frequency of the surface it is absorbed and becomes heat (if solid) or is scattered (if liquid or gas).
If it is NOT at the natural frequency
If incident angle is = to or less than the critical angle a refraction and reflection will occur
If incident angle is greater than critical angle only reflection will occur.
Critical angle produces refraction along interface

4. Refraction in General
Dfn: Change in direction of wave due to a change in speed
Velocity and wavelength changes, frequency remains constant
Fast to Slow (bend towards normal)
Slow to fast (bend away from normal)
Define refraction. How do frequency, velocity and wavelength vary for the incident and refracted wave? Which direction will the wave be bent when moving from a fast to a slow medium? How about a slow to fast medium?
Show Physical Science laser disk Chp. 28 refraction and wheel analogy
Show transparency and use above anology to derive bending of wave traveling from fast to slow. Generalize result by saying when going from fast to slow the ray will bend towards the normal.
Do the same for slow to fast
Describe how frequency is same because peaks will arrive at interface at same time interval. However wavelength will change because different velocity means wave travels longer or shorter distance in same period of time.

5. Examples of Light Refraction
Spoon in glass
Light after sunset
Stars and sun appear higher in sky
Pumpkin sun
Moon appears red during lunar eclipse red
Pyrex and Veggie Oil

6. Desert or Inferior Mirage
Occur when cold air over hot air
Eye assumes straight line path for rays
See a piece of sky on ground
Brain interprets waving as water
Question: Draw the conditions and light path for a desert mirage. Indicate the temperature gradient. What do our eyes actually see on the road?
Activity:
1) Show video of

7. Ocean or Superior Mirage
Hot air over cold
Upward directed light is bent away from normal and eventually ends up moving downward.
Occurs on North Sea
Eric the Red and the discovery of Iceland or Greenland

8. Sound Mirage Warm air over cool air
Usually occurs at night during summer
Sound waves bent over lake

9. Snell’s Law vrSin q i = visin q r Ni Sin q i = Nr sin q r
N = index of refraction = c/v
= speed light in vacuum / speed of light in substance
N>1
Qr = 90 deg at critical angle

10. Speed of Waves Light Sound Inversely related to the density.
Direct relationship with temperature
Directly related to density
Direct relationship with temperature