Jeffrey Lima

Polarization of LightMay 20, 2014

Partners: Walter Villatoro

Steven Meza

Conclusion

The Polarization of Light lab examined the transmission of light through two polarizing

filters as a function of the angle between their axes and compared it to Malus's law. The purpose

of the lab was to observe the change in light intensity of light passing through crossed polarizing

filters. The filters can be rotated so that the intensity of light increases or decreases depending on

the angle that the axis of one filter makes with the other. When the polarized lenses are

perpendicular to each other, theoretically, no light should pass, but there are no perfect polarizing

filters so some light is emitted. When the polarized axes are parallel to each other, the maximum

possible light passes through.

First, the light source, polarizing filters, and light sensor were placed so light

passed through the filters and then into the sensor. Only the rotatable filter will move to change

the transmission, the square filter in place, the light source, and the sensor must not move. There,

we then measured the intensity of light from a light bulb passing through a pair of filters using a light

sensor connected to a LabQuest and plotted an intensity vs. angle graph. One of the filters was rotated

from 0 to 360 degrees by 5 degrees each time to analyze the change in intensity of the light that passed

through the filters. At 0 degrees the axis of the filters were parallel and maximum intensity of light

passed through. As the filter was rotated, the intensity of the light decreased and increased a couple of

times as seen on the graph. The intensity decreased from 0 to 90 degrees where it reached its lowest

intensity and increased from 90 to 180 degrees where it reached its highest intensity. From 180 to 270

degrees it also decreased to its lowest and from 270 to 360 degrees it once again increased. These

increases and decreases made a graph of a cosine function which agrees with Malus’s proposition of

I=I 0cos2(θ). The graph shows that the lowest point at 90 degrees was not the same as the lowest

point at 270 degrees and the highest point at 0, 180, and 360 were also different although the lowest

and highest points should have all been the same. This was most likely due the sources of error involved

in this lab.

After finishing with the procedure with two filters, a third filter with its axis perpendicular to the

first was added and the same procedure was repeated except that in this procedure we did increments

of 15 degrees and started at the lowest intensity by mistake. Similar results were obtained from this

procedure. The intensity increased and decreased but for this part, it increased and decreased more

frequently. Instead of increasing or decreasing every 90 degrees, it increased or decreased every 45

degrees. The intensity vs. angle graph shows 4 increases and 4 decreases through 360 degrees.

Unfortunately the data from the first graph was erased due to a malfunction of LabQuest therefore we

were unable to make any comparisons between the data. But it can be seen that the second graph is

also a cosine function and is similar to the first which agrees with the formula I=I 0cos2(θ).

Sources of error:

LabQuest did not completely zero out degrees, it kept fluctuating around zero.

Accidentally moved light bulb from its "zero" position.

Different light entering the polarized filters from other lab group's experiment

Possible damage done to the polarized filters from previous use

Increments of degrees of rotation were estimated

Light source was possibly moved when rotating the polarized filter

Increments of 15 degrees does not give enough points to plot therefore graph is not a

smooth cosine squared graph

Parallax when labeling degrees on the analyzer filter