Materials

2x polarizers

Introduction

Light consists of oscillating electric and magnetic fields. The light from a source such as an incandescent lamp consists of different electromagnetic waves in which the electric field is randomly oriented in all directions. If for some reason we affect the light such that the electric field to some degree is oriented in a particular direction, then we say that the light is polarized. Studying the polarization of light can tell us if the source of the light interacts with the light to produce a polarization. This can in turn tells us about properties of the object such as shape or orientation.

In this brief activity we will study some properties of polarizers and how they can be used to learn about the polarization of light. A polarizer is a material that takes unpolarized light and gives it a preferred orientation, i.e. it polarizes the light. As we will see below, not only does a polaizer polarize light, but it can also be used to measure if light is already polarized

Procedure

Take a single sheet of the polarizer and look through it at the fluorescent lamps.

Q1. Does the lamp appear as bright when viewed through the polarizer?

Q2. Rotate the polarizer at least a half turn while looking at the fluorescent light. Does the light appear to change in brightness as you rotate the polarizer?

The fluorescent lamp is an example of an unpolarized light source. When viewed through a polarizing filter, only half the light will get through. When the filter is rotated you don't see any variation in intensity which means that the light had no initial orientation.

Q3. Now look through the fluorescent lamp with the first polarizer and take a second polarizer and rotate it at least a half turn between your eye and the first polarizer. Do you observe any effect this time?

You should observe that the lamp viewed through the second polarizer varies in intensity from the same to dark. That is because the light passing through the first polarizer is now polarized, i.e. it has a preferred orientation. When viewed through the second sheet oriented in the same way it appears the same.

Q4. How does the light appear when the second sheet is rotated 90° to the first?

Q5. Describe how you could look at light with a polarizer and determine if it is polarized.

D6. Your instructor will have you look at several light sources. Using a single polarizer, determine if the light source is polarized or not. Note, light can be only partially polarized so that you might see a change in intensity, but it may not disappear completely. Complete the table below.

Source	Was the source polarized?	Evidence