1. Light wave is coming out of page
Polarization
EM waves (light) are transverse waves
Perpendicular, oscillating electric & magnetic fields:
Light has a polarization angle
Only transverse waves have a polarization angle
E (electric)
B (magnetic)
Light wave is coming out of page

2. Most light sources are a random mixture of all possible angles
A polarizing filter transmits only the light waves with a certain polarization angle
The light is said to be “polarized”
source
light
rays
all orientations
source
polarizing filter
a single orientation

3. Polarized glare is block
When light is reflected it is often polarized
Polarizing sunglasses use this effect to block glare reflecting off shiny surfaces
Sun
Non-polarized light
Polarized glare is block
Shiny surface

4. Refraction

5. Refraction of Light
Light bends, or refracts, when it travels from one medium into another
Refraction is caused by the difference in the speed of light in different materials

6. Light is not the only wave that refracts:
All two- and three-dimensional waves refract when they enter a new medium

7. Light bends (changes direction) when it leaves one material and enters another
Thus the angle of refraction does not equal the angle of incidence i r
i ≠ r
refracted light
reflected light
incident light
normal line

8. Which way will the light bend?
It depends on the optical density of the two media
The more optically dense a material is, the slower light travels in that material
Light travels the fastest in a vacuum (v = c = 3.00×108 m/s)
A vacuum is the least optically dense medium
Diamond is one of the most optically dense materials (v = 1.24×108 m/s)

9. Going from less to more optically dense material:
Light is refracted toward the normal i r
Less Dense
More Dense
i > r

10. Going from more to less optically dense material:
Light is refracted away from the normal i r
Less Dense
More Dense
i < r

11. Index of Refraction
We define the index of refraction, n, as a measure of optical density:
n = c/v
c = speed of light in vacuum
v = speed of light in medium
n is always greater than or equal to one
Index of refraction is a dimensionless quantity
Example: Light travels at 2.25×108 m/s in water. What is water’s index of refraction?

12. A vacuum is the least optically dense medium with an index of refraction of n = 1.000000
Glass has an index of refraction of about 1.5 (How fast is light in glass?)
Diamond: n = 2.419

13. Snell’s Law of Refractionni nr
Snell’s law:
ni sini = nr sinr
i is the angle of incidence
r is the angle of refraction
ni is the index of refraction of material 1
nr is the index of refraction of material 2

14. Examples
A light ray traveling through air strikes a piece of glass (n = 1.5) at an angle of 42 from the normal. Calculate the angle of refraction.
A light ray leaves a crystal and enters water with an angle of incidence of 32.0 and an angle of refraction of 41.0. Find the index of refraction of the crystal.

15. Total Internal Reflection

16. Total Internal Reflection
Consider when light moves along a path from a medium with a higher index of refraction to one with a lower index of refraction:
Light is bent away from the normal line n1 n2
n1>n2 c

17. At a critical angle (c) the refracted ray is parallel to the boundary
This means that r = 90
Snell’s Law says: nisinc = nrsin(90)
 sinc = nr/ni for ni>nr
Example: What is the critical angle for a water-air boundary?
sinc = nr/ni = 1.000/1.333 = 0.750
 c = 48.6

18. The boundary becomes like a mirror!
Total internal reflection is the complete reflection that occurs within a substance when the angle of incidence is greater than the critical angle
The boundary becomes like a mirror! c

19. Fiber optic cable uses total internal reflection to guide light—like a light pipe!