PHY385H1F – “Introductory Optics” Practicals Day 7 – Intro to Polarization November 15, 2010 Please work in a team of 3 or 4 students. All members should find a way to contribute. Two members have a particular role, and these roles should change every week! Facilitator is the main person responsible for keeping the team on track with the activities. Recorder is the main person responsible for recording work in the notebook. At the top of each page of your notebook, please list the date and a page number. As the beginning of each day, list the names of all the partners in the team that were present, and note who is the facilitator and who is the recorder. (If anyone is late or must leave early, please make a note of this in the lab notebook when it happens.) Equipment Needed for Activities 7.1 and 7.2 Optical Bench Light Source Polarizers (2) Components Holders (3) Ray Table and Base Ray Table Component Holder Cylindrical Lens Viewing Screen Slit Plate Slit Mask Activity 7.1 – Linear Polarizers Figure 1. Set up the equipment as shown in Figure 1. Turn the Light Source on and view the Viewing Screen with the Polarizer removed. Replace the Polarizer on the Component Holder. Rotate the Polarizer while viewing the target. Note that the Polarizer is oriented so that its polarization axis is parallel to the line between 0° and 180°. [These polarizers from PASCO are absorptive filters, also called “Polaroid”. According to http://en.wikipedia.org/wiki/Polarizer , Polaroid of this kind… “…is made from polyvinyl alcohol (PVA) plastic with an iodine doping. Stretching of the sheet during manufacture ensures that the PVA chains are aligned in one particular direction. Electrons from the iodine dopant are able to travel along the chains, ensuring that light polarized parallel to the chains is absorbed by the sheet; light polarized perpendicularly to the chains is transmitted.” A. Does the viewing screen seem as bright when looking through the Polarizer as when looking directly at the target? Why? B. Is the light from the Light Source linear polarized? How can you tell? 10-11-21 7:13 PM PHY385H1F Optics Practicals Session 7 - Page 2 of 3 Figure 2. Now set up the equipment as shown in Figure 2. Note that both polarizers in the box are identical. Align Polarizer A so it transmits only vertically polarized light. Replace Polarizer B on the other Component Holder. Looking through both polarizers, rotate Polarizer B. C. For what angles of Polarizer B is a minimum of light transmitted? D. For what angles is a maximum of light transmitted? When you achieve this maximum, does the target seem as bright when looking through both polarizers as when you remove Polarizer B and look through Polarizer A only? Activity 7.2 – Linear Polarization by Reflection: Brewster’s Angle Figure 3. Set up the equipment as shown in Figure 3. Adjust the Slit Plate, Slit Mask and Ray Table and Base so that a single ray of light passes through the center of the Ray Table. Notice the rays that are produced as the incident ray is reflected and refracted at the flat surface of the Cylindrical Lens. (The room must be reasonably dark to see the reflected ray.) A. Rotate the Ray Table until the angle between the reflected and refracted rays is 90°. At what angle of incidence θi does this occur? Compare with an equation for Brewster’s angle from your Hecht text., and estimate the index of refraction of the glass, if you can. Arrange the Ray Table Component Holder so it is in line with the reflected ray. Look through the Polarizer at the filament of the light source (as seen reflected from the Cylindrical Lens), and rotate the Polarizer slowly through all angles. PHY385H1F Optics Practicals Session 7 - Page 3 of 3 B. Is the reflected light linear polarized? If so, at what angle from the vertical is the plane of polarization? Observe the reflected image for other angles of reflection. C. Is the light linear polarized when the reflected ray is not at an angle of 90° with respect to the refracted ray? Activity 7.3 – Some Polarization Definitions A. Define the following terms in your notebook: Linearly Polarized Light Unpolarized Light Dichroism Birefringence B. Do the polarizers used in activities 7.1 and 7.2 use dichroism or birefringence in order to work? Activity 7.4 – Malus’s Law - Theory A. Unpolarized light is transmitted through a linear polarizer, whose polarization axis is vertical. The initial irradiance before passing through the polarizer is 1 W/m2. What is the irradiance exiting the linear polarizer? B. Linearly polarized light with polarization vector vertical passes through a linear polarizer with an angle of 30° relative to the vertical. The initial irradiance before passing through the polarizer is 0.5 W/m2. What is the irradiance exiting the linear polarizer? C. Linearly polarized light with polarization vector 30° relative to the vertical passes through a linear polarizer with an angle of 60° relative to the vertical. The initial irradiance before passing through the polarizer is 0.375 W/m2. What is the irradiance exiting the linear polarizer? Activity 7.5 – [If you have time] Polarizing Sunglasses [worth 2 possible bonus points if all other problems are complete] Fishermen sometimes wear polarizing sunglasses, which they claim allow them to see the fish under the water easier. Do you believe this? Describe how such sunglasses might work.
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