1. How Light Behaves at a Boundary
Chapter 17-1
How Light Behaves at a Boundary

2. The Law of Reflection The angle of incidence equals
the angle of reflection
The angles are measured to the “normal” line
which is perpendicular to the reflecting surface

3. Regular Reflection Angle of incidence equals the angle of reflection
a smooth surface like a mirror causes regular reflection
light is reflected back to the observer in parallel beams

4. Diffuse Reflection Angle of incidence equals angle of reflection
Reflection from a rough surface results in diffuse reflection
light is reflected into a wide variety of angles

5. Refraction of Light
Refraction occurs when light changes direction at a boundary between media with different optical densities.
Remember: wave speeds are different in different media.

6. Snell’s Law
How does the angle of refraction depend on the angle of incidence?
Dutch scientist: Willebrord Snell, 1621
Ratio of sines of angles of incidence and refraction are a constant
The constant is called the Index of Refraction, n
or, in the more general case, written as

7. Light when it reaches a boundary can be both refracted and reflected:

8. Refraction: which way will the light bend?
More dense to less dense:
Bend away from normal
Less dense to more dense:
Bend toward normal

9. Light In a less optically dense medium Travels faster
has a lower index of refraction
a greater angle of refraction
bends away from the normal

10. Light In a more optically dense medium Travels slower
has a higher index of refraction
a smaller angle of refraction
bends toward the normal

11. Index of Refraction: a measure of the amount that light will bend
n of glass is less than n of water
—light bends less in glass than in water

14. Index of Refraction and the Speed of Light in that material
Reviewing: Index of Refraction:
A measure of the opitical density of a material
How much light bends when it passes into the medium
How fast light travels in the medium

15. Index of refraction of water = 1.33

16. End 17-1