The Penn State Electro-Optics Center - Science Demonstrations

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The Pennsylvania State University
Electro-Optics Center
© 2010

222 Northpointe Blvd
Freeport, PA 16229
Phone: 724-295-7000
Fax: 724-295-7001

Science Demonstrations

Silver Egg Demo
Permanent Thin Film Colors
Construct a Kaleidoscope
Exploring Color
The Color Mixing Turbine - Overlapping Color In Time
"Seeing" Beyond the Visible
The Bogus Barrier
Infinite Images
Camera Physics

Two students perform a science experiment

The following demonstrations are provided by:

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Silver Egg Demo

Silver Egg Demo Photo 01

Use tongs to hold a normal egg in a candle flame until it is covered with soot. Drop the soot-covered egg into a glass of water. A considerable amount of the light traveling through the water is totally internally Silver Egg Demo Photo 02

reflected when it encounters an air layer that adheres to the soot. Since most of the light is reflected, the egg appears to have a silvery, shiny surface. The egg will appear silvery until the air dissolves into the water, which only takes a couple of minutes.

Look closely to observe what happens to the small fraction of light that passes through the air layer.

Permanent Thin Film Colors

Light incident on a thin film, such as a thin layer of gasoline on water, will be reflected from the top and bottom surfaces of the film. When the reflected light waves exit the film, they interfere. This interference gives rise to the iridescent colors often associated with soap bubbles and oil slicks. These colors are as short-lived as the films that produce them. However, there is a way to capture the beauty of a thin film for posterity. Using a drop of inexpensive clear finger nail polish and a sheet of black construction paper, a thin film and its attendant colors may be made permanent.

Permanent Thin Film Colors

Obtain a pan or glass dish large enough to accept a 4" X 4" sheet of black construction paper. After filling the container with water, put the construction paper in the water making certain that it is completely submerged. Use the nail polish applicator brush to apply one drop of nail polish to the center of the water. The nail polish should quickly spread out over the surface of the water. After the nail polish has stopped spreading, slowly lift the construction paper out of the water. The nail polish should adhere to the surface of the paper. Allow the paper to dry. What do you observe on the surface of the dried paper? Remembering that the nail polish was colorless, can you explain the origin of these colors? Did you note that the colors change as you tilted the paper? Why does this happen?

Construct a Kaleidoscope

This activity is a hands-down favorite of our students! This "Lab in a Bag" includes three 1"X 6" mirrors and an instruction sheet. The sheet describes kaleidoscope construction and offers suggestions for creating a variety of objects to be viewed through the scope. The sheet also provides a brief explanation of image formation by the kaleidoscope and a history of the device. The resulting kaleidoscopes are absolutely stunning! Students often give their finished kaleidoscopes to family members and friends as gifts. Kaleidoscope Image 01

The mirrors used are cut from standard mirror tile available at any hardware or home supply store. You may cut the mirrors at home using a glass cutting tool; however, many hardware stores will cut the glass for free when they learn of your mission.

The simplest kaleidoscope is constructed by simply taping the three mirrors together with masking or electrical tape. The mirrors are placed face down and the tape is applied over small gaps left between the mirrors. These spaces allow the mirror assembly to be folded into a triangular shape. Without the gaps, the mirrors will bind. Kaleidoscope Image 02

When no object is permanently attached to the far end of the three-mirror system, the device is called a teleidoscope. View your world through the teleidoscope and be amazed! Everything seen through the teleidoscope is transformed into a beautiful, multi-faceted pattern. Attaching an object such as a decorated ping pong ball or test tube containing water and colored beads to the end of mirror system formally turns your teleidoscope into a kaleidoscope.

Exploring Color

Exploring Color 01

This "lab in a bag" allows students to explore principles of additive and subtractive color mixing. Along the way, they are made aware of examples of color mixing going on all around them. Each student is given six color filters (red, green, blue, cyan, yellow and magenta) and a pair of inexpensive diffraction glasses. The color filters need not be large. 2" X 2" squares will suffice. A small piece of diffraction grating taped over a hole punched in a file card may be used in lieu of diffraction glasses (see figure).

Students examine the makeup of white light by looking at an incandescent bulb through a diffraction grating. They record what they observe with crayons or colored pencils. They then place each color filter over the diffraction grating and see that each filter removes a different portion of the spectrum. If students use diffraction glasses, they should close the eye not covered by a filter. After making each observation, students should record their observations with colored markers. Color Spread and Goggles

To observe the effect of overlapping filters (subtractive color mixing), students view white light directly through various combinations of filters. (Note: a diffraction grating is not used in this portion of the experiment). The hope is that students will "discover" the rules of subtractive color mixing.

Placing a drop of water on a television screen or computer monitor reveals the wonders of additive color mixing. The drop, acting as a magnifying glass, reveals dots or rectangles of red, green and blue. Students realize that the myriad of colors seen on the screen result from the additive mixing of these three primary colors.

The Coloring Mixing Turbine - Overlapping Color In Time

Due to a phenomenon known as persistence of vision, our retina retains an image for a short time after the source of light has come and gone. Using persistence of vision, it is possible to combine colors by presenting them to the eye in rapid succession. If for example, a flash of red light impinges on the retina, the sensitive cones that are activated by the light continue sending signals to the brain for a fraction of a second. If a source of green light strikes the retina within this time, the brain will perceive yellow, the additive combination of red and green.

The color mixing turbine provides a simple yet elegant way of demonstrating the use of persistence of vision to achieve additive color mixing. Color Mixing Turbine Image 01

The following steps will guide you through the construction and use of the turbine.

1. Bend two corners of one of the black cardboard squares as shown in the figure to the right.

2. Attach a green sticker to one side of the card and a red sticker to the other. Make certain that the two stickers have overlapping areas. Experiment with the other stickers provided. Record your results. Color Mixing Turbine Image 02

Red sticker/Green sticker yields __________
Red sticker/Blue sticker yields __________
Blue sticker/Yellow sticker yields __________

Color Mixing Turbine Image 03

3. Gently hold the card by corners B and D using two fingers. By blowing on the concave blade, the cardboard can be made to spin. The alternating colors act as flashing red and green lights, the combination of which produces the sensation of yellow.

"Seeing" Beyond the Visible

While the eyes of some animals are sensitive to infrared (IR) or ultraviolet (UV) radiation, the human eye is, for the most part, not. Generally speaking, humans are privy to the very limited range of wavelengths lying between 400 and 700 nanometers. However, humans have learned to detect and even "see" beyond the visible spectrum with the use of a variety of devices.
UV-Sensitive Beads Before and After Sun Exposure

UV-Sensitive Beads Before and After Sun Exposure

Inexpensive UV-sensitive plastic beads provide one method of detecting sources of ultra violet light. The reusable, chemically treated beads under go a dramatic change in color when exposed to both UV-A and UV-B radiation. Students may be given several beads to take home to demonstrate the effect to their family and friends. By exposing the beads to radiation from as many sources as they can think of, students can lead an investigation that will inform and sometimes amaze parents. Potential sources include the sun, incandescent and fluorescent lamps, LEDs, television and computer screens, black lights, etc. After identifying strong UV sources (the sun and black light are usually determined to be by far the strongest), they can shield their beads from these sources with a variety of materials in an attempt to find the best absorber. Glass, plastic, water, suntan lotion are often used.

Television and DVD player remote control units emit IR. By directing the output from one of these remote control units at the lens of a digital camera it is possible to "see" IR. The normally invisible radiation will appear as a flashing dot when viewed on the active view screen found in both digital still and video cameras. The CCD (charge coupled device) in these cameras responds to IR, where the human eye does not.

The Bogus Barrier

Passing light waves through a polarizing filter results in light waves that vibrate in a single plane. Two polarizing filters with their polarizing axis crossed, that is, at right angles, will pass no light.

Setup Instructions: Cut a wide "window" in opposite sides of a shoebox. Cut a piece of polarizing film into four pieces, keeping track of the directions of polarization. Attach the film to the windows as shown, so that the two pieces in each window are polarized differently, but films directly across on the opposite window are polarized alike. Place a small ball in the box. Replace the lid. Provide another piece of polarizing film at the station for student investigation.

The Bogus Barrier 01

Have students examine the inside of the shoe box by looking through the tinted windows on either side. DO NOT OPEN THE BOX! Note that a wall divides the inside of the box into two regions. Tilt the box so that the ball rolls back and forth.

Does the ball pass through or bounce off the wall? Can you explain this mysterious behavior? If you are totally baffled, you may take the lid off the box. To discover why the "bogus barrier" exists, look through each of the windows with one of the square Polaroid filters provided at this station. You may find rotating the filter while looking through each window quite revealing!

Infinite Images

Use two 5" by 7" plastic mirrors. Drill a 3/8" hole in the center of one of them. Place the mirrors a few inches apart, facing each other. Place an object between the mirrors and look through the hole.

Observe the multiple reflections of the front and back of the object and how the reflections eventually fade away. Try an object that has different colors on the front and back. Try moving the mirrors closer together or farther apart, or angling them slightly.

Camera Phsics

Students learn about the workings of a camera by taking one apart. With the popularity of single-use cameras, it is possible to obtain a class set of used disposable cameras from virtually any camera store.

Students examine the camera's optics (these inexpensive cameras sometimes have up to three lenses!), flash electronics and film transport mechanism. They form images with the camera's principal lens and measure its focal length and f-number. Dissecting and analyzing a camera is one of our students' favorite take-home experiments.

Caution: Shock hazard! A charged capacitor in flash circuit may result in a severe shock. Discharge capacitor before student use. To avoid risk of shock completely, only use cameras without flash unit.

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