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Home Minds On Light Waves and Colors Mission LC2 Polarization Help Help 6

Mission LC2 Polarization

The Question

Unpolarized light passes through a first Polaroid filter and then through a second Polaroid filter whose transmission axes are aligned as shown. The light emerging from the second filter will have ____ the original intensity and be vibrating in a ____ plane of vibration.

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.

Minds On Time

The diagram shows unpolarized light entering two consecutive filters. The transmission axes of the filters are aligned perpendicular to each other - one vertical and one horizontal. Unpolarized light will enter the first filter and exit as polarized light. The plane of polarization for the light exiting the first filter will be perpendicular to the transmission axis of the second filter. Thus, any light exiting the first filter will be blocked by the second filter. The combined effect of both filters is to block all the light.

Think About It

Polarization by Transmission Through a Filter:
A Polaroid filter is a device that polarizes light. The filter serves to filter out one-half of the vibrations of unpolarized light as the light passes through the filter. Unpolarized light enters the Polaroid filter and polarized light exits the filter with one-half the original intensity and with vibrations in a single plane. The unpolarized light becomes polarized.

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