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Physics 30: eLab Activity

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Polarization

Background:

When light travels, it vibrates in all planes perpendicular to the direction of the movement of the light. The concept of polarization is rather simple - a polarization filter allows only the light that is vibrating in a particular plane to pass through it. Light that has passed through a such a filter is said to be "polarized" because it is vibrating only in a single plane.

In this lab, you will experiment with a light sensor to determine the effect polarizing filters have on unpolarized light.

The Question:

How does polarized light differ from unpolarized light?

Variables:

This experiment involves these variables: number of polarization filters, position of polarizing filters, light intensity. Identify and state the manipulated, responding, and controlled variables in this investigation.

Materials:

  • light sensor
  • light source
  • USB link
  • 2 polarizing filters
  • lab stands and clamps

Procedure:

Step 1:

Plug the light sensor into the USB link (which is connected to the computer).

Step 2:

Using lab stands and clamps, arrange the light sensor and light source so that the light source is shining directly into the light sensor with a small amount of space in between.

Alternatively, this experiment can be done on an optics bench system, with the light source and light sensor facing each other. If this approach is taken, it may be also useful to use a polarizer accessory that mounts in between the light sensor and the light source:

Step 3:

Configure the DataStudio software with a light intensity graph.

Step 4:

Turn on the light source and note the light intensity reading. Place a single polarizing filter directly in front of the light sensor. Slowly rotate the filter and note any changes in your light intensity graph. Place a second polarizing filter right behind the first. Now slowly rotate the second filter, noting any changes in your light intensity graph.

Analyzing and Interpreting:

1. What was the effect of a single polarizing filter on the intensity of the light? Explain why this occurs.
2. What was the effect of rotating the single polarizing filter? Explain the result.
3. What was the effect of adding a second polarizing filter? If the intensity of the light changed with rotation of the second filter, explain why.

Forming Conclusions:

4. Write an answer to the following question:
  • How does polarized light differ from unpolarized light?

Extending:

5. Polarizing filters are often used in sunglasses. Design an experiment to determine whether particular sunglasses are equipped with polarizing lenses.
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