1. The Polarization of Light
SPH4U

2. Unpolarized Light
The direction of the variation of the electric field of an electromagnetic wave may be in any direction perpendicular to the propagation.

3. Polarized Light
However, the variation may be in a single direction. In this case, light is said to be linearly polarized.

4. Polarized Light
However, the variation may be in a single direction. In this case, light is said to be linearly polarized.
Only the vertical components of the variation pass through.

5. Polarization and Intensity
Unpolarized light passed through a polarizing filter has ½ its original intensity:

6. Filtering
However, already polarized light passed through a polarizing filter may be unaffected (if the filter is in the same direction) or reduced to zero (if the filter is at 90o).

7. Two Filters
So the intensity of light passed through two polarizing filters is angle-dependent:
(Malus’ Law)

8. 3D Movies
Movies can be made to look 3D by projecting what is to be seen by the left eye at a different polarization to what is to be seen by the right eye. The viewer wears a filter to block the other eye’s polarization over each eye.

9. Polarization by Double Refraction
Light may be polarized by refraction in certain materials (e.g., calcite crystal). This is called double refraction because the index of refraction depends on the polarization and the light will travel two paths.

10. Polarization by Reflection
Light may also be polarized by reflection from non-metallic surfaces. The polarization will be parallel to the surface.

11. Polarization by Reflection
Photographs of a window with a camera polarizer filter rotated to two different angles (at 90o from each other):

12. Brewster’s Angle
The amount of polarization will depend on the angle of incidence and will be 100% if the reflected and refracted rays are at 90o to each other.
This angle is called Brewster’s Angle

13. Example
What is Brewster’s angle for water (n = 1.33)?

14. Example
What is Brewster’s angle for water (n = 1.33)?

15. Example
What is Brewster’s angle for water (n = 1.33)?

16. Example
What is Brewster’s angle for water (n = 1.33)?

17. Example
What is Brewster’s angle for water (n = 1.33)?

18. Example
What is Brewster’s angle for water (n = 1.33)?

19. Example
What is Brewster’s angle for water (n = 1.33)?

20. Example
What is Brewster’s angle for water (n = 1.33)?

21. Example
What is Brewster’s angle for water (n = 1.33)?

22. Polarizing Sunglasses
Many sunglasses have vertical polarizing filters to remove glare reflected from horizontal surfaces.

24. Why is the sky so much a deeper blue?

25. Polarization by Scattering
Light can also be polarized by scattering in the atmosphere, so polarizing lenses can also reduce scattered light and improve contrasts in the sky in photographs.

26. More Practice
“Polarization Activity”