# Week 14

Read: Crystal symmetry and light rotation (Chap. 23), Light scattering (Chap. 24)
Quiz: None.

Homework:
1. Birefringence, quarter wave plates, and circular polarization (Ex. 23.1),

Lab: This week we will do four labs, each of them short, and each of them illustrating some aspect of light polarization.
1. Brewster's angle (Ex. 22.2). Place a glass plate on a surface under an unpolarized light source. Inspect the light reflected from the surface. Now place a polarizing filter between the glass plate and your eye. Determine the incidence angle such that the reflected light is completely polarized. From this (Brewster's) angle, determine the refractive index of the glass plate. Is it consistent with your previous measurements using snell's law?
2. Light rotation (Ex. 23.2): Qualitatively observe various materials when place between crossed polarizing filters. Materials include a third polarizing filter, thin flakes of mica, cellophane tape, stressed plexiglass, and ice crystals. You should take photographs of each with appropriate lighting and describe as clearly as possible how you carried out your experiments and what you observed.
3. Tyndall scattering (Ex. 24.2): Place clear water with a drop or two of skim milk added into a square cuvette on the lab bench. Illuminate the water with a HeNe laser beam. The water should still be clear; the milk merely increases the scattering to make the laser beam passing through clearly visible. Now observethe laser light that is scattered from the milk/water solution using a polarizing filter. You should do this from several vantage points. Is the scattered light polarized? If so, in which direction. To be unambiguous, make a sketch of the laser, the cuvette, and the (several) observation locations. Include a coordinate system and clearly indicate the orientation of the polarization from each observation point. Note: "horizontal" and "vertical" polarization are ambiguous terms when viewing the cuvette from above.
4. Rayleigh scattering (Ex. 24.3): On a clear bright day, identify the location of the sun. Choose a clear blue section of the sky and observe it through a polarizing filter; do not look directly at the sun. Is the blue light scattered from the sky that is reaching your eye polarized? If so, in which direction? Be as clear as possible; draw a diagram indicating the location of you, the sun, the observed portion of the sky, and the direction of polarization (if any).

Chapter 23 (3 videos):

Chapter 24 (1 video):

Physics 2