Linearly polarizedlight

In transparent tape, long polymer molecules are stretched parallel to the length of the tape. Light polarized parallel to the stretch of the molecules travels through the tape more slowly than light polarized perpendicular to the stretch.

Polarization oflightnotes PDF

A note about the tape used in this Snack: Before you buy large quantities of transparent tape, test the brand you're buying by placing a strip of the tape between two pieces of polarizing material. For convenience, you can actually stick the tape to one of the polarizers, and then rotate the other polarizer against it. If the tape changes from dark to light, or vice versa, you can use it in this Snack. If the tape remains the same shade of darkness when you rotate the polarizer, it won't work here.

The liquid crystal displays (LCDs) on most computer monitors and laptop screens polarize the light that comes from them. You can verify this by looking at a LCD screen through one of your polarizers. You can try this Snack by putting tape directly on a LCD screen. The tape will look clear, but you can reveal the mosaic any time by looking at the screen through a polarizer.

Circularly polarizedlight

When polarized light enters the tape, its direction of polarization will probably not line up with the length of tape. If the light is polarized in a direction that does not line up, its direction of polarization will be resolved into two perpendicular components. One of these components will be parallel to the length of the tape, and one will be perpendicular.

The thicker the tape is, the more out of step the components will become, and the greater the change in the polarization will be. If, for example, the two waves recombine after one has been delayed by one-half a wavelength, the direction of polarization of the light will be rotated by 90 degrees.

What is plane polarizedlightin Chemistry

Using transparent tape and polarizing material, you can make and project beautifully colored patterns reminiscent of abstract or geometric stained-glass windows. Rotating the polarizer as you view the patterns makes the colors change. With a little creativity, you can also create colorful renditions of objects or scenes.

Every material has an index of refraction, which is the ratio of the speed of light in a vacuum to the speed of light in the material. Light travels through the tape you used in this demonstration at two different speeds. (Materials with this property are called birefringent, which is derived from the Greek words for “doubly refracting.”)

Plane polarizedlight

White light is made up of light of all different colors, or wavelengths. Since the index of refraction of the tape is different for each color of light, each color has its own unique pair of speeds as it passes through the tape. The result is that the polarization of each color is changed by a different amount for a given thickness of tape.

The waves that compose these two components are initially in step with each other. But as they travel at different speeds through the tape, they go out of step—that is, the crest of one wave no longer lines up with the crest of the other. When these out-of-step light waves emerge from the tape on the other side, they recombine, making light with a polarization different from that of the original light.

Polarized and unpolarizedlight

When a second piece of polarizer is placed over the tape and rotated, it transmits different colors at different angles. This accounts for the color combinations you see at a given angle, and for the changes in color as the polarizer is rotated (click to enlarge diagram below).

The colors you see here result from differences in the speed of polarized light as it travels through the transparent tape.