Optical Phenomena

Thin-Film Interference

Interference effects are also noted when there are very thin films, approaching the dimensions of a ______of light. Light traveling in one medium encounters a thin film with a different index of refraction. Some of the light is transmitted through the film while some of the light is reflected off of the top surface. The light that travels into the new medium encounters another boundary, and some is transmitted and some is reflected.

When the thickness of the film is a multiple of ______of the wavelength of the light, the waves interfere to reinforce that specific color. The colors change as the ______of the film changes, and the ¼  is met at different locations for different colors. This causes iridescence in bubbles, on sea shells, on oil slicks, compact disks, etc.

Polarization of Light Waves

Light is an electromagnetic wave, consisting of ______and ______fields propagating at right angles to each other. Ordinary light is ______meaning that all directions of the electric field are equally probable and lie in a plane perpendicular to the direction of propagation. ______light emits only one direction of the electric field.

Unpolarized Light Polarized Light

A ______is a material that polarizes light through selective absorption by oriented molecules. Molecules readily absorb light whose electric field vector is ______to their lengths and transmit light whose electric field vector is ______to their lengths (called the transmission axis).

The first polarizing filter is called the ______. This filter always absorbs ____ of the intensity of light. The second polarizing filter is called the ______. It will absorb a portion of the transmitted light, depending on the angle of the axis between the analyzer and the polarizer. If the axes are parallel, then the analyzer absorbs ______. If the axes are perpendicular, then the analyzer absorbs ______. At any other angle, in between 0º and 90º, the analyzer will transmit a fraction of the light that hits it.

035c59860886ea706c171b69a3f3e0fc.doc A good analogy for polarization is skipping stones across the water: if the stone’s flat side is parallel to the water surface, the stone will ______. Glare from a horizontal surface is ______polarized. Polarized sunglasses can help reduce glare by being ______polarized.

3D Viewing The glasses have two Polaroid filters. Each filter has a different polarization axis - one is horizontal and the other is vertical. In a 3D movie, there are two projectors also having two different polarizing filters. The result of this arrangement of projectors and filters is that the left eye sees the movie, which is projected from the right projector, while the right eye sees the movie, which is projected from the left projector. In a still photo, there are two superimposed images, one with a heavy emphasis on red colors and the other on blues. The glasses have one eye with a blue filter and the other a red filter. In either situation, the filters create slightly offset images, which create the perception of depth or illusion of a 3-Dimensional object.

Optical Illusions Our bodies, and for that matter most living things, have special cells called ______receptors. They can detect light, sound, temperature, pressure, odor, taste, pain, pressure, balance, etc. Most of these receptors are on or near the surface of the body such as our eyes, ears, tongue, etc., but some are internal.

Each sensory receptor detects its own special form of energy and transmits a signal to the brain. The reception of the signal in the brain represents sensation. How the brain interprets these signals and makes them meaningful is called ______. Illusions are ______that are perceived by most people, and are based on a specific stimulus received under certain conditions. Optical Illusions are fun to look at and come in many categories, including ambiguities, figure-ground, impossible, distorted, kanzia, typographical, color after-effects, and motion after-effects, to name a few. Optical illusions are only tricks on your brain and aren’t really physical issues at all.

Practice Questions 1. In what direction does the light end up polarized after passing through the following sequence of filters?

a. b. c. d. e. no direction

2. Is polarization characteristic of all types of waves?

3. Why would depth not be perceived if you viewed 2 identical ordinary slides in a stereo viewer, instead of a pair of slides taken with a stereo camera?

4. An ideal polarizing filter transmits 50% of the incident nonpolarized light. Why is this so?

5. How many legs does this elephant have?

6. Is it moving and shimmering?

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