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Home Minds On Light Waves and Colors Mission LC2 Polarization Help Help 8

Mission LC2 Polarization

The Question

A fisherman wishes to purchase some Polaroid sunglasses that are capable of blocking the glare resulting from reflection of sunlight off lake water. Consider the choices shown below. The lines represent the transmission axes of the filters. Which pair(s) should he/she purchase? List all that apply in alphabetical order with no commas or spaces between letters.

Physics Rules

Polarization by Reflection off a Nonmetallic Surface:
Unpolarized light often becomes partially polarized when it reflects off a nonmetallic surface such as the calm waters of a lake or an asphalt roadway. A portion of the reflected light becomes polarized in a plane that is parallel to the reflecting surface.

Minds On Time

Light reflecting off a lake is often partially polarized (see Know the Law section above). The polarization occurs in a plane parallel to the reflecting surface. That is, most of the reflected light is vibrating horizontally (since the water surface is aligned horizontally). This polarized light can produce an annoying glare to a fisherman. A common way to reduce the glare is to wear sunglasses equipped with Polaroid filters. It is important that the filters be oriented in such a manner as to block the horizontal vibrations. The Know the Law section describe the relationship between the transmission axis and the plane of vibrations that are blocked.

Physics Rules

Polaroid Filter and the Transmission Axis:
A Polaroid filter is said to have a transmission axis. The filter can be thought of as having long-chain molecules that are aligned within the filter in the same direction. Unpolarized light can be thought of as consisting of waves with electric and magnetic components of vibration that are directed in a multitude of planes. The electric and magnetic components that are aligned in the direction of the molecules become absorbed by the molecules. Those components that are perpendicular to the molecules emerge from the filter. Thus, the transmission axis is aligned perpendicular to the molecules of the filter. One-half of the original vibrations emerge from the filter. The emerging vibrations are aligned in a direction perpendicular to the molecules and parallel to the transmission axis.

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