Vernier Software and Technology
Vernier Software & Technology

Polarization of Light

Figure from experiment 28A from Physics with Vernier


Perhaps you have seen a display of polarized sunglasses in a store. You can quickly test to see if the glasses are really polarized by looking through the lenses of two glasses and rotating one pair by 90°. If both pairs of glasses are polarized, the lenses will appear to go black. Why is that?

To explain the darkened lenses, we need to think of the light as an electromagnetic wave. An electromagnetic wave has varying electric and magnetic fields perpendicular to the direction the wave is traveling. This experiment focuses only on the electric field variation, represented by a vector. Light emitted from a typical source such as a flashlight is randomly polarized, meaning that the electric vector points in varying directions.

An ideal polarizing filter will remove all but the electric fields that are parallel to the axis of the filter. The light remaining is then said to be polarized. A second filter can be used to detect the polarization; in this case, the second filter is called an analyzer. The transmission through the second filter depends on the angle between its axis and the axis of the first filter. In this experiment you will study the relationship between the light intensity transmitted through two polarizing filters and the angle between the filter axes.

In the 1800’s Malus proposed a law to predict light transmission through two polarizing filters. The relationship is

I = I0cos2θ

where I0 is the intensity when the angle θ between the polarizer axes is zero. In this experiment, you will see if this law is useful in describing your polarizing filters.


  • Observe the change in light intensity of light passing through crossed polarizing filters.
  • Measure the transmission of light through two polarizing filters as a function of the angle between their axes and compare it to Malus’s law.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Standards Correlations

See all standards correlations for Physics with Vernier »

Experiment 28A from Physics with Vernier Lab Book

<i>Physics with Vernier</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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