Optics Demonstrations with an Overhead Projector

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Optics demonstrations with an
overhead projector
Douglas S. Goodman
Douglas S. Goodman, "Optics demonstrations with an overhead projector,"
Proc. SPIE 2525, 1995 International Conference on Education in Optics, (13
October 1995); doi: 10.1117/12.224000
Event: SPIE's 1995 International Symposium on Optical Science,
Engineering, and Instrumentation, 1995, San Diego, CA, United States
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Invited Paper
Optics Demonstrations with an Overhead Projector
Douglas S. Goodman
Polaroid
Optical Engineering Department
38 Henry St.
Cambridge, MA 02139-4894
Magic Lantern, John Zahn, 1685
From Eugene Ostroff, Smithsonian
"Photographic Enlarging: A History,"
Photographica Journal, Vol 1, No 3 (1984)
The idea for these demonstrations occurred when, while preparing a demonstration for a course, I realized
that I was reinventing the overhead projector. Because the projector is so readily available, I undertook
to see how much could be done with it using additional inexpensive and readily available materials. No
fundamental novelty is claimed, since projectors have been around for at least 300 years, and people have
probably tried most everything. Moreover, most of these demonstrations are variations on classics that
can be done in many ways. The purposes of this work are to point out just how much can be done so
easily on the projector, to provide guidance in optimizing the demonstrations, and to provide information
on vendors and useful materials. Most important, I hope to encourage people to do demonstrations. The
projector is obviously ideal for many demonstrations of human vision, but I have not undertaken these,
leaving them to specialists in the field.
INTRODUCTION
Demonstrations are good, overhead projectors are common and inexpensive, and much can be done with
the projector quickly, easily, and with inexpensive materials.
The Importance of Demonstrations
People are visual creatures. Much of the brain is devoted to vision. People are attracted to bright lights,
autumn leaves, television, computer graphics, and visual stimuli of all sorts. Language is filled with
visual metaphors, an example being the term "color' as used in music. Appearances are important.
Seeing is believing, remembering, and reinforcing. Now, in the Age of Simulation, demonstrations have
new importance as a counterbalance to complete dependence on and faith in what computers—with their
alluring visual outputs—produce.
Advantages of the Overhead Projector
Overhead projectors are commonplace, and inexpensive, with prices starting at about $250. Expensive
projectors are not necessary for demonstrations, and, indeed, projectors with "bad" performance can be
used to show aberrations. Projectors are safe—UL approved and built for general use. Projectors supply
a major portion of many experimental setups. In particular, they contain a strong lamp, with cooling,
electrical power supply, and condensing lens a substantial part of the apparatus that for many optical
demonstrations is the most trouble and least interesting.
The additional materials required for most of the demonstrations described here are inexpensive, some
being everyday objects. Many of the purchased items are obtained from educational—as opposed to more
pricy scientific—vendors, as well as, for example, theatrical supply stores. Many of the fabricated parts
are plastic that can be made in a machine shop or carpentry shop, buffed smooth, rather than figured from
glass in an optical shop.
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Demonstrations are not, in themselves, associated with any educational level or age group. This is a
matter of how they are discussed and explained. Demonstrations can be presented in a number of ways.
Youngest audiences can be approached with a 'gee whiz' treatment, emphasizing that the world is
interesting and surprising. Demonstrations can be used to cultivate curiosity, with the participants
playing to see what happens. Demonstrations can be used as reinforcements to lecture material. Some
demonstrations are directly related to applications, for instance, metrology. Here instrumentation, rather
than 'pure' physics is concentrated upon, providing appeal for 'practically minded' students. Some
demonstrations are related to appearances, why things look as they do, curiosity about which is to be
nurtured, since the environment provides endless objects of study. A number of concepts that might be
considered advanced can be introduced with demonstrations, possibly without explicit mention for junior
audiences. These include symmetry, special orientations, parity, resolution, convolution, and differential
measurement.
These demonstrations are designed to be done quickly, so they can be inserted in a lecture in 'real time.'
Whenever possible, the demonstrations employ comparisons, for instance, between a beam of light that is
acted on somehow and a "control" beam. Motion and change are used to capture attention, and colors for
aesthetic appeal.
These demonstrations can be done in ways other than the standard "teacher in the front" mode. They can
be done as student experiments or presented to the students as problems or even oral exam questions.
The Projector and the Laser
When the laser appeared, some demonstrations and experiments, especially those of interference and
diffraction, became very much simpler, so they began to be done with lasers. The laser became more
familiar and less expensive and began to be used increasingly, while important non-laser demonstrations
were forgotten. The overhead projector demonstrations complement those of the laser very nicely; what
the laser does best cannot be done on the projector, and the projector does much that the laser cannot do at
all, an obvious example being white light demonstrations.
The Overhead Projector
Overhead projectors differ enough to affect the optimization of some of these demonstrations.
Consequently, you should familiarize yourself with a projector before undertaking a demonstration. Most
of these demonstrations either cannot be done well or cannot be done at all with the portable reflected
light overhead projectors that have a Fresnel mirror on their platen..
A study of the projector is worthwhile since the principles and components of projectors are common to
many instruments. Lift the hood and see what is inside. Different projectors can be compared to see the
various ways in which the same problem has been treated, as well as methods of inexpensive mass
production. In addition to the optics, there is electrical power, cooling, safety interlocks, mechanical
mechanisms for lamp switching and lamp focus. The optics systems include the lamp, illumination
optics, imaging optics, and a mirror.
The illumination optics captures as much of the lamp's output as possible, produces reasonably uniform
irradiance at the platen, and directs the light into the imaging lens. The Fresnel lens under the platen
images the lamp in to the lens. Show the lamp by holding an additional lens projector and the screen,
where the lamp is imaged. Improve the quality of the lamp image by covering the platen with a piece of
cardboard with a hole cut out, to stop down the Fresnel lens, thereby reducing its aberrations.
The mirror performs three functions. (1) It produces a vertical image of a horizontal transparency. (2) It
permits the speaker to face the audience while the transparency is seen upright. (Bowling alley projectors,
for which everyone faces the same direction, are different.) (3) It reverses parity. The speaker and
audience see the transparency and its image in opposite directions relative to the projector axis.
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To demonstrate the parity change produced by a mirror, hold a mirror just after the projector lens,
producing an image on the wall, floor, or ceiling of reversed parity. Move the mirror to show that the
image parity stays the same, although its orientation changes.
A part of the projection system is the screen, which is designed to scatter the light incident upon it into a
range of angles subtended by the audience. Show the screen's angular scattering properties by taping
different materials to it, for example white paper and aluminum foil. Walk around the room to see how
the relative brightness of the different surfaces change with position.
Some Practical Tips
.
Block out the irrelevant portion of the illuminated field with a platen field stop to eliminate space in
which nothing is happening, to concentrate attention, and to reduce the light in the room. A
generally useful stop is a white cardboard sheet covering the platen with a rectangular hole about
7"x9". Dark cardboard absorbs and warms.
.
Energy densities are greatest where the lamp is focused, usually just below the projection lens, so be
careful about placing color filters, polarizers, and other materials there. Plastic can melt and paper
can ignite. This can be used to show that radiation transfers energy, for example, by putting a beaker
of water with a thermometer at the focus. To reduce the power at the focus, block some of the light
with a field stop on the platen or place on the platen an IR absorber, for instance one of the sheets
used with theatrical lights.
S
Eliminate distracting stray light emitted from various openings in the projector base. This light is not
noticed in ordinary use, but is detrimental to demonstrations. To check for stray light, cover the
platen completely and turn on the projector in a dark room. In obstructing these openings, do not
block cooling air. A loop of tape often does the job.
.
Many demonstrations require additional field stops that can be cut from thin cardboard. A
particularly useful one has a single hole in the center about 1cm in diameter. Another has a slit the
same width. A cutout letter F, or something else that shows parity, is useful.
.
.
.
Eliminate unwanted moire effects involving the projector Fresnel lens by raising the demonstration
material on a sheet of glass or plastic and refocusing.
Color filters sold by theatrical supply houses are most generally useful. They are large, relatively
inexpensive, and are designed to withstand heat. Rosco sells a "swatch book" of filter samples with
spectral transmission curves.
"Ripply glass," such as that used in shower doors is useful. It can be obtained from stores that supply
hobbyists who work in stained glass windows, Tiffany-type lamps, and so forth. The appearance on
the projector of these materiajs is difficult to predict, so it is best to get a variety. (This material can
produce fascinating diffraction patterns when illuminated by a laser.)
• A strong diffuser on the platen results in too weak an image, since too much light is scattered beyond
the lens. A useful diffuser is Rosco #110.
• Projectors can be used backwards, by using the lens to image onto the platen, covered with a suitable
screen material, for instance, white paper.
• For many experiments requiring two projectors, one can be a slide projector.
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. Pairs of projectors can be used in a number of ways. Two patterns, images, or colors can be overlaid.
One projector can be used to produce an image on a screen, and another to reimage it onto the platen.
For some demonstrations, the second projector can be a slide projector.
.
An object that must be vertical can be projected as follows. Place it in the center of the platen. On
one side, set a mirror at 45° to produce an image in the platen plane. On the other side set up a
mirror angled to direct light from the base through the object and into the projection lens.
.
Darkfield illumination can be obtained and objects can be illuminated transversely from one or more
directions by using mirrors on the platen and an opaque sheet under the object. However, this is
inefficient.
.
The projector base can provide illumination for other demonstrations. If the lens is removed, the
application can be placed above the base. Alternately, a mirror can be used to redirect the light
horizontally.
.
The projector base can produce a somewhat collimated beam. Find the location on the platen of the
best beam empirically by blocking most of the platen with a stop that is moved about it.
.
A light table can be made by covering the base of the projector with a sheet of milky plastic or opal
glass.
.
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Many transparencies can be made easily, without photographic processing. Transparencies can be
made on thermal copiers and on many photocopiers, so patterns found in books and catalogues, for
example resolution targets and patterns that produce good moire effects, can be used. Copiers with
enlarging and reduction capabilities are available. Computer graphics can be readily produced..
A turntable with a hole in the center can be made from RubbermaidTM lazy susans sold in
supermarkets for a few dollars. Holes, which need not be precise, can be cut in the centers.
MONOCHROMATIC GEOMETRIC OPTICS
Plane Parallel Plate
To show axial image shift, place a grid on half the platen and above it a glass or plastic plate or a beaker
of water. Refocus the lens to show an axial shift. Hold another grid next to the plate, and move it axially
until it is in focus, showing the location of the image and that the axial shifting does not change lateral
scale.
Show translation by tilting a clear plate over a marked transparency. Use different thickness plates, side
by side if possible, to show that translation varies with thickness for a given angle. An application is the
optical micrometer, in which small image shifts are measured by tilting a thin plate over an angle large
enough to be easily measured.
Demonstrate a scanner using a plastic cube with two handles on opposite sides. Cover the platen except
for a single hole, and the rotate the cube with the handles. An application is in high-speed film cameras
where the film does not come to rest to expose each frame.
Thin Prism
Show the monochromatic properties of the thin prism with a clear plastic prism, about 100mm x 100mm
with an apex angle of about 100. On the platen place a cardboard with a letter "F" cut out, and cover the
opening with a green filter, since dispersion is not to be shown here. Hold the prism at the projector lens.
Tilt the prism to change the deviation angle and to show the minimum deviation angle. Rotate the prism
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to move the image on an arc without rotating it, as a mirror would do. Compare prisms of the sanie
material but different apex angles and prisms with the same apex angle made of different materials. Move
a prism across the projector lens pupil to produce two displaced images with varying amounts of light. A
variable-angle prism can be made by placing together two thin prisms and rotating them.
Patterns in Shallow Water
Simulate caustic patterns like those seen at the bottom of shallow water by placing on the platen a piece of
ripply glass of the kind used in shower doors. Tilt the glass to show the change of contrast with depth of
water.
Total Internal Reflection
Show total internal reflection with a plastic 45° prism, placed over a hole in a piece of cardboard on the
platen. A piece of diffusing tape on the output face serves as a screen to make the outgoing beam visible.
Cut one end of a plastic bar at about 45° and smooth the end. Hold the angled end near the lamp image
and light traverses the bar laterally. Internal reflection is shown with fluorescent plastic sheets, as
described below.
Retroreflector
With an open platen, hold a plastic bicycle reflector at the screen and its observe its appearance from
different places in the room. Similarly, hold retroreflective material against the screen. The screen itself,
as discussed above, is somewhat retroreflective.
DISPERSION
Show dispersion with a glass prism at the projection lens, with the platen covered except for a small
central hole. A chromatically dispersed image of the hole is seen, and tilting the prism shows that the
minimum deviation angle varies with wavelength. Show that refraction angles vary with material by
using a pair of prisms of different materials with the same angle. A plastic prism can be made to match
the shape of an existing glass one. Cover the platen with a cardboard from which a slot has been cut. The
resulting spectrum on the screen is curved, since the rays from the various points in the slot make
different angles with the prism. Slits in spectrometers are curved for this reason. Another object with
which to show dispersion is a plastic cone with a large apex angle, which gives a colored circle on the
screen.
The chromatic aberration of the projector Fresnel lens provides another demonstration. Block the platen
except for an opening near an edge, and hold a white card under the projector lens to see a chromatically
aberrated image of the lamp.
Rainbow
The rainbow can be demonstrated with a single plastic ball. Hold a viewing screen near the projection
lens on the audience side, and hold the ball in the light leaving the projector to produce a rainbow-like
pattern on the screen. This requires some experimentation. There is not much light, so reduce stray light
with a platen cardboard from which part of an annulus is cut out, blocking much of the light that does not
contribute to the rainbow. Use a light blue color correction filter on the platen to enhance the blue end of
the spectrum. An analogous demonstration can be done with a plastic cylinder and a field stop with a
straight slot.
IMAGING
Record images by projecting onto paper taped to the wall or onto a whiteboard or a blackboard. Images
can be traced and measurements made with rulers and protractors.
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Miscellaneous Properties
Measure transverse magnification. by putting a clear plastic ruler on the platen, measuring its image, and
finding the ratio.
Show orthographic imaging and keystone distortion with a clear plastic grid on the platen projected onto a
screen at various angles. Tilt the object grid over the platen, and measure the sizes and angles of image
features.
Rotate the transparency and show that the image rotates identically.
Demonstrate front and rear projection and parity by projecting an appropriate pattern on a screen that can
be viewed from both sides, for instance tracing paper or thin cloth. Flip over the transparency on the
platen to show parity reversal, and rotate the transparency in the platen plane to distinguish between
orientation and parity.
Show vignetting with a piece of cardboard with a hole cut out, held at various places between the platen
and lens.
To show imaging reversibility, turn the projector off, cover the platen with a white paper to act as a
screen, and image a bright external object onto the platen.
Introduce auxiliary lenses either before or after the projector lens to show how image size and location
change. Translate and tilt these lenses to show other properties.
To show relationships between the distances between object and lens and between lens and image, move
the transparency above the platen, move the projection lens, and move the projector as a whole toward or
away from the screen.
Resolution and Empty Magnification
To demonstrate resolution limitations, use a transparency with a variety of feature sizes. One can be made
by photocopying a picture of a resolution target from a book or catalogue. View the image from near the
screen to observe that images of smaller features become blurrier and fmally indistinguishable. With a
good projection lens, the resolution of an image viewed from the normal audience position is limited by
that of the viewer's eye, so the limitations of the projection lens are not observable. Project a piece of
microfiche so that its geometrical image is sufficiently large that the letters ought to be readable. They
remain unreadable, even when observed at the screen with a magnifier. Magnification and resolution are
not matched.
Phase Structures
Various properties of phase structure images can be shown with ripply glass. If a grid on the platen is
covered with a weak ripply glass, the image is distorted, but remains sharp. If the glass is moved to the
lens, the image is blurry. This shows the difference between looking upward through the atmosphere
from the earth' s surface and looking downward from above, as from a satellite. Move the ripply glass
between the platen and the lens to show the transformation between the two extremes.
Twiniding Stars - Imaging Through Turbulent Material
Simulate turbulent media by translating ripply glass. To imitate the twinkling of stars, use weak
"Aquatex" style ripply glass and a cardboard on the platen with several 5mmholes to represent the stars.
Phase Objects and Magnitude Objects
Some objects, known as magnitude objects, such as a cardboard with holes, either pass or block light.
Others, known as phase objects, such as ripply glass, pass all light, but deflect it in various directions.
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The images of magnitude and phase objects have different properties, especially as regards their
dependence on illumination and changes through focus. Such properties, which are often seen most
clearly with microscopes, can be demonstrated with the overhead projector. When a cardboard with holes
is defocused, its image basically becomes a blurred version of what is seen in focus, but the image of a
ripply glass changes in form. For a weakly rippled glass, image contrast may be greater out of focus,
unlike a magnitude object. The defocused images of a magnitude object are nominally the same on both
sides of focus, but this is not the case for phase objects. An object that combines both magnitude and
phase attributes can be created by placing a ripply glass on a patterned cardboard.
Defocus
Defocus effects differ for projectors with different types of illuminations. Periodic objects when imaged
defocused are nearly periodic, and make interesting patterns. Periodic plastic materials are fairly common
and these can be tried. Tilt the materials on the platen to simultaneously show different amounts of
defocus. Change the effects of defocus by adding a weak diffuser at the platen.
Ray Aberrations
Show that a blurred image can be decomposed into a number of differently shifted images. Hold a piece
of cardboard with a hole about 5mm in diameter at the projector lens and translate it. The image on the
screen is sharp for each hole position, but it moves when the hole is moved. Thus rays passing through
different parts of the lens aperture do not intersect the screen in the same place.
Aberrations and Resolution
Overhead projector aberrations can be increased with a diffuser on the platen that sends light through the
full aperture of the lens, rather than through only the portion for which it is best corrected. Observe the
image of a resolution target with and without a diffuser.
Astigmatism
Some projectors have enough astigmatism for a simple demonstration. Using a pattern with orthogonal
sets of lines at the edge of the field, move the projection lens through focus to show that lines at different
orientations are sharpest at different focal positions. With better corrected projectors, obtain astigmatism
by placing above the pattern on the platen a cylindrical lens with a focal length of about 300 mm.
Weaken a stronger cylindrical lens by immersing it in a petri dish of water or oil. Orient the cylinder at
an angle above a square pattern to make a parallelogram image.
Chromatic Aberration
Observe lateral color with a field stop that has a slit at the edge of the field parallel to the side of the
platen. Stand near the screen to best see the colored image. Produce displaced images by covering half of
the slit with a red filter and half with a blue one.
Observe chromatic aberration indirectly by using a color filter with a resolution test target, showing that
the image is sharper when the wavelength range is decreased.
Observe the chromatic aberration of the Fresnel lens as described in the dispersion section above.
Dividing the Pupil for Multiple Images and Special Effects
Insert a thin prism part way across the projector lens pupil to produce double images. With a multi-part
platen, one image can be made to change to another. Image changing can also be done with an object
made of polarizers at different angles and a rotating analyzer at the lens. Likewise, an object can be
composed of different color filters with a changing filter at the lens.
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Knife-Edge Test
The knife edge test can be demonstrated on a projector whose lamp has a small filament and no integral
reflector. Raise the projector lens to make the filament image accessible, and introduce a heat-insensitive
knife edge. The object is a piece of ripply glass, raised from the platen so as to produce a focused image
with the raised lens.
Projection Contour Determination
Project a grid on a three dimensional diffuse object, e.g. a plaster of Paris shape, to show a method of
determining contours.
Contrast Reduction and Background Light
Use one projector to produce an image on the screen, and another to provide a uniform background,
showing the effects of contrast reduction. Relative irradiances can be varied. With color, there are
additional possibilities.
Face-to-Face Projectors
With two projectors pointing at each other, several methods of re-imaging can be shown. With nothing
between them, a small field of view can be obtained if the alignment between the two projectors is precise.
A screen can be put between them, on which an intermediate image is formed, providing insensitivity to
projector, but with much lost light. Finally, a large Fresnel lens with a long enough focal length can be
used as a field lens, producing a brighter image with a field as large as the Fresnel lens.
Field Lens and the Eye
In a variation of the above, attempt to view the aerial image formed by a projector. Next add a screen and
then a Fresnel field lens. The observer's eye lens and retina then act as the second projector and platen
screen in the above demonstrations. For direct viewing, greatly reduce the amount of light, so as not to
damage the eye.
MOIRE
Moire phenomena are particularly easy to demonstrate. There is extensive literature on moire, and almost
anything involving flat transparencies works on the projector, including many everyday objects, such as
screens, cloth, perforated sheet, and combs. A kit sold by Edmund ($6) is useful. For the projector, two
should be obtained. Use the variable enlarging feature of the photocopier to make patterns with different
periodicities to show phenomena related to beating and group velocity.
Hexagonal patterns, which are not commonly used for moire, provide excellent effects. These patterns
can be produced on the computer. Another source is perforated metal. An interesting effect is obtained
with a relative rotation of two such pieces, about 250mm on a side. Put a pin in the center of the lower of
the two, so the upper one can rotate around it. The smoother sides of the punched sheets should be in
contact.
Moire is usually demonstrated black and white, but fascinating color effects can be obtained. For
example, overlay two checkerboard or bar transparencies with different pairs of colors. Try a pair of
identical hexagons, each consisting of the subtractive primary colors.
Show applications of moire in metrology and alignment, where small motion produces a large change in
appearance. Overlay and translate equally spaced lines, concentric circles, etc. Moire accentuates the
difference between two nearly identical patterns, a technique used in optical inspection.
Separate one sheet from the other, possibly tilted, to show what happens. Show that a coarse moire
pattern is insensitive to defocus, although the individually contributing patterns are blurred. With two
projectors, overlap on a screen the images of two transparencies. If the images of each are resolved, a
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moire pattern results, but if they are not, no pattern will be seen. Show the moire pattern that arises
between the projector Fresnel lens and a transparency above it.
SCATTERING
Surface Scattering
A piece of ground glass on the platen produces a dark image because it scatters light beyond the lens.
Accordingly, when viewed from near the platen, the ground glass appears lighter than its surround. Put
two different types of diffusers side by side on the platen, and compare brighinesses on the screen and
brightnesses viewed from near the lens. Show that the scattering results from a combination of a
roughened surface and a refractive index mismatch between air and glass. Put the ground glass in a petri
dish and pour in water to reduce the scattering by more nearly matching the refractive index of the glass.
Use mineral oil for a better index match and still less scattering.
Linear structures scatter most efficiently in directions perpendicularly to themselves. Make an object to
demonstrate this by abrading a piece of plastic sheet, about 100mm on a side, mostly in one direction.
This can be done manually or by holding the plastic against a belt sander in one orientation, producing a
number of scratches in roughly the same direction that do not have the regularity of a grating. Block the
platen, except for a small centered hole, and hold the plastic piece at the projection lens to produce a
scattering distribution perpendicular to the lines. Rotate the scattering piece and the scattered light
distribution rotates with it.
Particle Scattering
Show particle scattering by dropping particles into the beam leaving the projection lens. Partially block
the platen to confine the beam, and darken the room by projecting the light against an absorber.
Blackboard erasers can be beaten above the beam or baking flour can be sprinkled in. Any kind of safe
dust can be used. Cigarette smoke works, as does water droplets from dry ice.
Rayleigh Scattering
Use a flat-bottomed, clear-sided vessel nearly tall enough to fill the space between the platen and the
projection lens. Flat bottomed jars are rare in the supermarket, but chemistry glassware can be used, or a
vessel can be made by gluing a flat piece of clear plastic, enlarged to be a stable base, to the end of a clear
plastic tube. Cover the platen except for an opening smaller than the vessel, located where the light from
the platen is most perpendicular to it. Nearly fill the vessel with water and add a small amount of milk or
non-dairy creamer. The amount needed must be found experimentally, and is best added with an eye
dropper. The scattered light appears as a column in the liquid. Hold a polarizing sheet beside the vessel
and rotate it to show that the light is polarized with the E vector horizontal. Too much milk results in
multiple scattering, which gives unpolarized light. Hold a polarizer above the vessel to demonstrate that
the unscattered light is not polarized.
The unscattered light, projected to the screen is reddish because of the wavelength dependence of Rayleigh
scattering. To emphasize the color change, use an additional hole in the field stop to transmit light that
does not traverse the scattering liquid. Since the projector lamp has a lower color temperature than the
sun, the scattered light does not look blue. Add a color correction filter to enhance the blue.
To show what happens when the incident light is polarized, place the vessel on a linear polarizing sheet
on top of a rotation table with a central hole. Rotate the entire system, and the irradiance, as viewed from
a point in the audience varies. Nearby observers might need to close one eye to maximize the contrast.
Liquid scattering experiments should be set up in advance optimize the formulation. It may also be
necessary to get rid of air bubbles on the sides of the vessel, which can be removed with a long stirring
rod.
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Other Scattering Demonstrations
Show multiple scattering by adding more milk. As the amount is increased, there is less and less
transmitted light, and the column of light first seen in the vessel becomes a general glow. With a certain
amount of milk, the numbers of singly and multiply scattered photons are comparable, in which case
rotating a polarizer outside the vessel shows that some of the light is polarized and some is not. With still
more milk, virtually all photons are multiply scattered and rotating a polarizer shows nothing. Observe
forward scattering by standing over the projector and looking down at a scattering beaker.
Scattered light can be observed in order to study dissolution and flow. For example, if an eyedropper of
milk is added gently to water through which light from the projector base passes, the slowly changing
distribution of the milk can be seen.
Show concealment by scattering, such as occurs with fog, turbid water, and paint. Put a petri dish of
water above a transparency on the platen. Add various amounts of milk to the dish and observe the
disappearance of the transparency's image. Alternately, arrange several petri dishes with the same
amount of water and different amounts of milk, or with the same amount of milk in different amounts of
water. Tilt a petri dish to show the variation of concealment with thickness. A transparency with
different feature sizes shows that fine features are affected more than the coarse ones.
FLUORESCENCE
fluorescing substances are readily available. These include "thy-glow" paper, posterboard, markers, and
red plastic drafting tools. Some laundry powder fluoresces, as does its water solution. Another liquid is
Prestone antifreeze, which should be diluted in water. Plastic sheets are available from distributors, who
might have scraps. There is luminous paint, e.g. Edmund F31,806 ($10), and safety tape sold by
industrial suppliers. Chlorophyll can be extracted from plant leaves.
From a magenta-looking fluorescent plastic sheet, cut out a disc or square about 100mm across, and
smooth the edges. This can be done with woodworking tools. Hold this piece under the projection lens
and orange light is emitted. It is most intense at the edges because the fluorescent light is emitted in all
directions from points within the plastic, and much of this light is guided by total internal reflection to the
edges of the plastic piece. To show that there is a wavelength change, put a green filter over the platen,
and orange light still appears. To demonstrate that the fluorescent plastic absorbs, put it on the filtercovered platen to produce a black image on the screen. This last demonstration does not work if the
excitation is by the UV. Let the light that has passed through one fluorescing sheet pass through a second
one, which emits less. Try fluorescers with different absorption bands in series, and switch their orders.
To show that absorption varies with wavelength, put side by side on the platen strips of red, green, and
blue transparencies. Put a piece of fluorescent plastic across these strips, covering half of each. It is seen
on the screen that the light passing through the three is diminished differently by absorption. (Note here
that what is perceived as one color may have other spectral components. This can be checked with the
spectroscope described below.) Fluorescent plastic itself can be used as a filter in this demonstration.
With a sheet polarizer, show that the plastic fluoresces regardless of the polarization of the incident light,
that the polarization of the nonabsorbed light is not changed, and that the emitted light is not polarized.
Fluorescent posterboard, paper covered with fluorescent paint, paper marked with fluorescent markers,
etc. can be held against the screen and excited by the projector light. Analogues of the above experiments
can be done with transmitting color filters on the platen.
GRATING
The best grating period for overhead projector demonstrations is about 10im, i.e. 100 lines per
millimeter. One such grating is the Central Scientific 8648001 ($30). Most gratings sold for education
purposes have too small a period, so the diffracted light falls beyond the screen, and the light is too spread
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out and too dim. Mount the grating in a square piece of cardboard about 100mm on a side to obstruct light
that does not pass through the grating. Hold the grating near the projection lens, both before and after it.
Many gratings have equal lines and spaces, so the there is little light in the even number diffraction
orders, except for the zeroth.
Basic Grating Properties
Cover the platen except for a hole about a centimeter in diameter and hold the grating after the projection
lens. Observe the diffraction orders and the sequence of colors. Rotate the grating about the central ray to
swing the orders in an arc. Tilt the grating in the principal plane perpendicular to the orders to produce
asymmetrically separated orders, so that, for instance, the distance between the 0 and +1 orders differs
from that between the 0 and —1 orders. Tilt the grating in the principal plane parallel to the lines to
produce orders that intersect the screen on an arc. (In direction cosines, everything is linear.)
Use gratings with different periods to show how the separation of the orders changes.
Hold a grating under the projection lens and move it up and down, changing the separation of the orders
on the screen, which can be thought of as images of "virtual orders" that are backward extensions to the
platen of the diffracted light.
Replace the field stop with a hole with one with a slit for more light. Compare prisms and gratings,
showing the difference in the sequence of colors and that gratings can provide more dispersion.
Multiple Gratings
Put one grating after another to produced an array of orders of orders, each order of the first grating
giving rise to multiple orders of the second. Rotate the gratings relative to one another to skew the
pattern. If the grating lines are perpendicular, the array is square for gratings of the same period, or
rectangular if the period are different.
A number of interesting effects can be produced with crossed gratings. Mount the crossed grating under
the projection lens so that it can be rotated about its axis, and put a turntable with a central hole on the
platen. Place various objects on the turntable and rotate both them and the grating. With a cardboard that
has a single slit cut out, a pattern like that of a water wheel is produced. Perforated metal gives
interesting patterns. Another object is a cardboard with random holes. The image is a messy collection of
shapes and colors that can be used as an example of the common scientific endeavor of decomposing a
confusing situation into pieces that can be understood. Insert color filters to show that the pattern can be
spectrally decomposed. Block out all but one of the holes to show spatial decomposition. Combine the
two decompositions. A good perpendicular crossed grating is the "Rainbow Symphony Spectrostar" ($8).
With a polarizer, show that diffraction angles do not vary with polarization, although the amount of light
may vary.
Color Addition
A grating can also be used as a means to demonstrate some color addition phenomena. With multiple
holes in the field stop, different orders can be overlapped in various ways to produce additive color effects.
To add spectra that are reversed, cut two parallel slits about 50mm apart in a cardboard that is placed on
the platen. Above the platen, hold a grating with the lines oriented parallel to the slits. Move the grating
up and down to cause the +1 order from one slit to overlap the —1 order from another slit, adding red and
violet to give magenta.
SPECTROSCOPE
Make a spectroscope by mounting a grating after the projection lens and covering the platen except for a
slit, whose position is chosen for best viewing on the screen. Place various colored objects on the slit and
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observe their spectra. The zero order shows their appearances, providing qualitative demonstrations in
color vision, showing, for example, that something that looks yellow may contain other colors. Show the
tradeoff between resolution and power with slits of different widths or with a wedge-shaped slit. The
narrower the slit the more saturated the colors, but the less light.
Among useful objects are: Colored plastic sheets and color filters. Magenta is instructive, as is yellow,
which may contain red and green. Transparency markers on transparencies work. Didymium glass
(available from Rolyn Optics and elsewhere) has distinct absorption bands, and fluorescent plastics
usually have a single dark band. Interference filters can be tilted to change the color of the light they
transmit. Colored liquids can be put in petri dishes or the like.
With an unsaturated colored plastic sheet, make a staircase of one thickness, two thicknesses, and so on.
In the zero order the color becomes more saturated, and the spectrum become more confmed.
Do side-by-side comparisons by putting samples next to one another on the platen slit. Overlap samples
for color subtraction.
Do "astronomical speciroscopy" by using the projector in reverse. Place a white paper screen on the
platen and a grating at the lens. Look out a window at night to observe the spectra of star surrogate
sodium and mercury street lights.
INTERFERENCE COLORS
Interference colors can be shown on the overhead projector. Put a transmitting interference object above
the platen and observe the color of its image. Tilt the object to change the color. Some objects are
polarization-sensitive enough that the colors can be changed by rotating a polarizer before or after some
them. The platen can be blocked except for two or more holes to compare with white light or with light
that has passed through another filter.
Reflect light directly from the object to the screen. This light is not imaged, so a blur is produced, but it is
colored. If the filter absorbs little, the transmitted and reflected colors are complementary, and the filter
can be oriented to overlap the two beams, giving a white sum.
Inexpensive filters are Edmund color separating dichroic filters, P43,45X, where X =4,5,6,7,8, about $12
each, and American Science & Surplus dichroic filters, about $5. "Iridescent" gift wrapping sheets show
angular dependence. A thin film deposition company may be able to provide rejected material that is
excellent for qualitative demonstrations.
Most everyday examples of interference are in reflection, e.g. thin oil fthns in parking lots. To observe
reflection interference colors, block the platen except for an off-center opening and use a mirror to reflect
light to a tilted object and thence to the projection lens. This requires a lot of apparatus.
POLARIZATION
Polarization phenomena are dramatically and colorfully demonstrated. Most demonstrations employ sheet
polarizer, which need not have the highest extinction. In general, avoid colored polarization material, so
the colors arise entirely from wavelength-dependent phase shifts. Both linear and circular polarizers are
useful, and circular material can be reversed and used as linear polarizer. Sheet waveplates are also
useful. Some material is available in small, inexpensive pieces. Material that can be had only in larger
sheets can be cut up and divided between a number of people.
Basic Polariscope Arrangement
Convert an overhead projector into a polariscope as follows: Set up a rotatable polarizer on the platen.
Above this, put a rotation table to hold the object under study. Topmost is a rotatable analyzer. Separate
the turntables with thin wood sheets with holes. Rubber bottle stoppers, which have a lot of friction, are
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good for this. The analyzer can be mounted on such a turntable or on a separate stand that holds it under
the lens. All the apparatus should be located between the platen and the projection lens, since the
projection lens/mirror assembly affect polarization. Locate color filters above the analyzer or below the
polarizer, since they may be birefringent. Make comparisons by putting objects side by side or by leaving
an empty space next to the object being observed. To show the orientations of polarizer, analyzer, and the
objects between them, make pointers of birefringent plastic that show up, in general differently colored,
for all orientations.
Show that the projector lens/mirror assembly affects polarization by placing a polarizer on the platen and
an analyzer alternately before and after the lens.
Two Polarizers
Show the change of transmittance with the relative angles of two polarizers. Show that there are two
extremes of light and dark per revolution.
Three Polarizers
Set the polarizer and analyzer to extinction and introduce a third polarizer between them at an arbitrary
angle, resulting in light at the screen. Rotate the inner polarizer, giving four cycles of brightness per
rotation. Similarly, set the outer polarizer and analyzer parallel, and insert between them another
polarizer that reduces the light, and whose full rotation gives two cycles of irradiance.
Determining Polarization Orientation with a Half Shade Device
When an analyzer is rotated relative to a polarizer, it is difficult to find the positions where the two are
parallel and perpendicular, since the irradiance is an extremum. The positions can be found more easily
and more accurately with the half-shade device. Cut a piece of polarizer so one reference edge makes an
angle with a principal direction. Cut two pieces from this one. Flip one over and contact the two portions
of the original reference, so the principa' directions of the two halves angles with the common edge.
When this pair is rotated in linearly polarized light, there are four angles at which the two halves are
equally bright, when the edge is perpendicular and when it is parallel to the direction of polarization.
This is an example of differential detection, in which the eye compares the brightness of adjacent fields,
which can be done to do a few percent.
Multiple Polarizers and Analyzers
A variety of effects can be obtained by juxtaposing pieces of polarizer cut at different angles relative to
their principal directions. With orthogonal pieces acting as a dual polarizer, followed by, say, a piece of
plastic and an analyzer, two relative orientations can be seen at once. Similarly, strips of polarizer cut at
different angles can be put together. With similar analyzer strips at right angles, a matrix of polarizer and
analyzer angles is produced.
Waveplates
Waveplates, or birefringent plastic sheets, can be put between polarizer and analyzer and rotated. Such
waveplates have a color dependence, which can be suppressed with a color filter or demonstrated using
white light or possibly with different color filters side by side on the platen. Show that there are two
principal directions by rotating a waveplate between polarizers. Show that two quarter wave plates in the
same orientation acts like a half wave plate, that orthogonal identical wave plates cancel, and so on. An
array of waveplates of the same type oriented differently makes an interesting display.
Circular Polarizers
Make a circular polariscope by replacing the linear polarizer and analyzer with circular polarization
material, usually a left-handed and a right-handed pair. Such a pair would ideally extinguish light,
regardless of their azimuths, but in practice there is chromatic variation, and demonstrations work best for
a particular relative azimuth. Suppress chromatic effects with a color filter transmitting around the design
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wavelength of the circular polarizers. Place various objects in this polariscope and compare their
appearances with those in the linear polariscope. Rotate the objects. Show that a linear polarizer and a
quarter wave plate make a circular polarizer.
Calcite Crystals
Calcite crystals are usually not as large as is desirable. One way to help is with an auxiliary lens or with
an enlarging unit designed to show 4"x5' transparencies on a projector. Make a small hole in a piece of
cardboard and place the crystal above it, resulting in two spots. Rotate the crystal and rotate polarizers
before and after. Add a second crystal to split each of the spots into two more spots, depending on the
orientation. To make a thicker crystal, put one on top of the other, possibly with index matching materiaL
The orientations are matched when the combination produces two spots rather than four. A good buy is
Ward's 49E1602, a 4cm x 4cm crystril for about $18.
Mica
Hold a piece of mica between polarizer and analyzer and change its orientation to show interference
colors.
Stress Birefringence
Many materials are birefnngent when stressed. Polycarbonate, sold under various trade names such as
LexanTM, is very sensitive. Pieces of polycarbonate can be twisted and bent by hand between polarizer and
analyzer, and models of structures, e.g. bridges or buildings, can be made and stressed in various ways, for
example with thumb screws. Many plastic sheet products that are stretched during manufacture have
permanent stress, observed qualitatively by rotating them between polarizer and analyzer. Many plastic
objects, such as rulers, protractors, CD boxes, and food containers are birefringent. Try all clear plastic
objects. With molded plastics, differential cooling results in stresses, so the location of the mold gate can
be seen. Plastic bars, plates, and other shapes may have birefringence resulting from their manufacture.
For example, some cubes show the same kind of pattern in two orientations, but a different one in the
third, suggesting that they were cut from an extruded bar. Some bars show different patterns in all three
directions, suggesting that they were cut from plates. Stress lines can be mapped by setting the
polariscope with crossed polarizer and analyzer and projecting the pattern on a white screen where the
blackest regions are marked. The polarizer and analyzer are then rotated a little together and the dark
lines are marked again. Continuing this process maps the stress lines. This procedure and others are
discussed in books on photoelasticity.
Optical Activity
The polarization azimuth of linearly polarized light rotates as it passes through an optically active
material. Light Kar0TM corn syrup is a readily available optically active material. Karo syrup is water
soluble and easy to dispose of. It keeps for a long time, and can be reused. Pour the syrup in advance,
since there may be bubbles that float upward very slowly. Place a vessel of the syrup about six inches deep
with a fairly flat bottom between polarizer and analyzer, producing a color from incident white light.
Rotating the vessel has no effect. Put a color filter before or after the polariscope and rotate the analyzer
to show that light of the wavelength being viewed is nearly linearly polarized, but at a different angle.
Switch to a different color, which is also linearly polarized and rotated, but at a different angle, so
dispersion causes the color change with white light incident. Two colors can be compared simultaneously
with two filters, each blocking half the beam. Compare vessels with different depths of syrup. To show
continuous thickness variation, cut a strip of sheet polarizer in a principal direction and put it in the
vessel at an angle. Remove the polariscope polarizer, and rotate the analyzer, giving a dark band that
moves along the polarizer strip. Orthogonally polarizing strips show bands 1800 out of phase. Between
circular polarizers, the syrup has no effect. To demonstrate rotation in both directions, obtain levorotary
and dextrorotary sugars from a chemistry supply house.
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Polarization from Reflection and Transmission
It is possible to show changes of polarization with transmission by holding plastic sheets at large angles
between polarizer and analyzer. However, the effect is not dramatic. Multiple sheets can enhance the
effect, as in the pile of plates polarizer.
Observe transmission at all angles simultaneously with a plastic dome between polarizers. The dome
material must not be birefringent. A large dome is Edmund Scientific C71,710 for $22. Another source
is the "plastic eggs" that hold small toys in vending machines at supermarkets and so forth. Soap bubbles
can be used. With the polarizer and analyzer crossed, observe the dark cross, whose orientation is that of
the principal directions of the polarizers. Rotate the dome to show its rotational symmetry. Rotate the
polarizer and analyzer together. Set the polarizer and analyzer parallel to give a complementary pattern.
To show changes of polarization upon reflection, use black glass or smooth black plastic to eliminate
multiple reflections. Put a polarizer on the platen and a rear projection screen vertically on the front edge
of the platen. The plastic is held at an angle of about 45°to reflect the light on to the screen. The platen
must be obstructed except for a small opening, since the light leaves it over a range of angles. Vary the
angle of the plastic and that of the polarizer to show Brewster's angle. To compare different
polarizations, make a field stop with two or more holes, each covered by linear polarizers at a different
angles, including those that give s and p polarizations. Tilt the black material to show that reflectivity
varies with incident polarization.
Spectral Analysis Of Polarization Effects
Analyze polarization phenomena spectroscopically by combining the polariscope and the spectroscope.
Cover the polariscope platen with a cardboard with a slit and add a grating after the projection lens.
Conoscoopic Effects
Sandwich thin birefringent materials between a polarizer and analyzer and hold the stack after the
projection lens. This uses the projector as a small source oflight with a range of angles. The lamp should
be without internal mirrors, and the effect may be enhanced by obstructing the pupil so as to pass only
light from the filament. The quality of these demonstrations varies with the projector.
Depolarization
Observe depolarization by projecting light onto the screen with a polarizer following the projection lens.
Observe the screen through an analyzer held at the eye to see that the light is not completely polarized.
Try other screen material, including aluminum foil, which is better at preserving polarization. Such
screen considerations are necessary for three-dimensional motion pictures based on polarization.
Order of Elements
The order of elements matters in polarization. Between the polarizer and analyzer place two elements and
then reverse their order. In general, the result changes. This is an example of non-commutativity in
physics. A related fact is that polarization elements can be mathematically represented by matrices, the
product of which represent a series of elements, and matrix multiplication is not commutative.
1800 Rotation Periodicity
Between polarizer and analyzer, anything can be rotated 1800 and the appearance is unchanged. Likewise
the polarizer or analyzer can be so rotated. Show this with homogeneous material such as birefnngent
sheet or polarizing sheet. More interestingly, use an irregular looking object, e.g. some stressed plastic.
Circle a region of fairly uniform color to keep track of it. As the object is rotated, the colors shift and
change, but after half a revolution the color in the marked region returns to what it was originally.
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Principal Directions and Flipping
Place a flat homogeneous object, for example a birefringent sheet, between polarizer and analyzer and flip
it about an axis parallel to the platen. In general the output changes, but there are two special orthogonal
directions about which the material can be flipped with no change.
ACKNOWLEDGMENTS
I have freely harvested published material on demonstrations, modifying them as necessary for the
overhead projector. A number of people have made useful suggestions, including Tom Ainsworth, Sam
Batchelder, Russell Chipman, Paul Coteus, Paul Doherty, Keith Jenkins, Glen Johnson, John
Geievenkamp, John Hayes, Arwin Marathay, Betty Moore, Bill Plummer, Doug Smith, Eberhard Spiller,
Richard Sonnnenfeld, Phil Stahl, and Jack Taylor. Additional suggestions are solicited.
SOME SUPPLIERS
Information as of February, 1993
Am Plastics 800.431-2451T
American Science & Surplus 708.475-8440 Evanston, Ill 60202 Inexpensive.
Bruce Pine Mica 704.765-4241
Central Scientific Company (CENCO) 800-26-CENCO Franklin Park, Ill
Edmund Scientific 609.547-3488
General Science Materials Company 714.534-0985 10123 Crosby Ave Garden Grove, CA 92643
Great American Market 213.461-0200
theatrical supplies
Hudson Glass 800.431-2964 Peekskill, NY 10566 ripply glass
International Polarizer 508.481-7495 Marlborough, MA
Learning Technologies Inc. 800.537-8703 59 Walden St. Cambridge, MA 0214 grating material
Polaroid polarizer division 800.225-2770
Rainbow Symphony 818.708-8400 6860 Canby Ave Unit 120 Reseda, CA 91335
Rolyn Optics 818.914-5707 Covina, CA 91722
Rosco 914.937-1300, 213.462-2233 Port Chester, NY theatrical supplies
Science Kit & Boreal Laboratories 800.828-7777 Tonawanda, NY 14150
Solargraphics 501.525-1776 Box 7091J Berkeley , CA 94707 (sold through Edmund)
Ward's 800.962-2660 Rochester, NY
PURCHASED EQUIPMENT - partial list
OVERHEAD PROJECTOR
Plane mirror, Plexiglas - CENCO 6cm x 9cm #70703 $2
Fresnel lens - American Science and Surplus, Ward's $2
Overhead projector accessories - audio visual distributors
Turntable - Rubbermaid No. 2936 at supermarket
MONOCHROMATIC GEOMETRIC OPTICS
Plastic cubes, sheets, etc. - Am and other distributors
DISPERSION
Prisms of same angle and different material Spindler & Hoyer #33300 300 prism BK7 $125, #33 3310 300 prism FK2 $125
IMAGING
Grid transparency -package of 10 Ward's 15E2911 $8
Ripply glass - stained glass window supply places, glass shops, e.g. Hudson
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Cylindrical lens - Rolyn Optics #14.0450 $55 60mm x 50mm x 300mm fi
Eyeglasses ?
Enlarger - Polaroid #691 $200 , Buhi #26-067 $150
MOIRE
Moire patterns for the study of interference - General Science Materials H-1003 $12
Edmund Scientific kit
Perforated metal - Small Parts Inc. Miami 305.751-0856
Ronchi rulings - Edmund, Rolyn
SCATTERING
Petri dishes - Edmund
reusable polymethylpentene P35,296 $39 for 10, disposable polystyrene P38,026 $17 for 100
Ground glass - Edmund, CENCO 7.5cm x 10cm #86002 $3
FLUORESCENCE
fluorescent plastic sheets -plastic distributors, e.g. Am
One manufacturer is Robin & Haas 215.592-3000
INTERFERENCE
Interference filter American Science & Surplus, Edmund
GRATINGS
For grating demo and spectroscope
Basic grating: 100 1/nun
Also 200 1/nun , 300 1/nun , 600 1/nun
CENCO clear area 45mm x 45mm $27 ea. , set for $91 #86247-01
Set of diffraction gratings 100/nun, 300/nun, 600/mm and crossed gratings 300/mm - General Science
Crossed Grating
Rainbow Symphony Astrastar $8
Solargraphics Jupiter Window (sold through Edmund)
SPECTROSCOPY
Color filters - Rosco, Great American Market, Edmund, etc.
Didymium glass - Rolyn
Fluorescent plastic
POLARIZATION
Linear polarizer sheet - International Polarizer, Polaroid, Edmund, etc.
Circular polarizer - Polaroid
Left hand 605230 $120 19"x50" , right hand 605229 $200 19"x 50"
Wave plate
Polaroid - big sheets
International Polarizer 4" square, package for 5 for $25
quarter wave for 550nm, 400nm, 480nm, 640nm and half wave for 520nm, 580nm,
Mica - Bruce Pine Mica 704.765-4241
Calcite (also listed as Iceland spar) -Ward's 49E1602 4cm x 4cm xlcm , $17
Polarization demonstrator set with calcite crystals, benzoic acid, polarizer -CENCO, Ward's, others $35
Karo Light Corn Syrup - supermarket
SOME BOOKS ON DEMONSTRATIONS AND EXPERIMENTS
M.Cagnet, N.Francon, J.C.Thrierr, Atlas of Optical Phenomena Vol.1 (Springer-Verlag, Berlin, 1962)
M.Cagnet, N.Francon, S.Mallick, Atlas of Optical Phenomena Vol.2 (Springer-Verlag, Berlin, 1971)
R.W.Wood, Physical Optics (Macmillan, New York, 1911; Optical Society of America, 1988)
C.F.Bohren, Clouds in a Glass of Beer. Simple Experiments in Atmospheric Physics (Wiley, New York,
1987) l95pp
C.F.Bohren, What Light Through Yonder Window Breaks? (Wiley, New York, 1991) l9opp
G.F.C.Searle, Experimental Optics (Cambridge U.P., 1925) 357pp
M.Francon, M.Krauzman, J.P.Mathieu, M.May, Experiments in Physical Optics (Gordon & Breach,
New York, 1970) Zllpp
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E.Deeson, ed, Light an ASE Lab Book (Asociation for Science Education, John Murray, London, 1975)
86pp
H.Palmer, Optics Experiments and Demonstrations (Johns Hopkins, Baltimore, 1962) 320pp
Newport Research and D.O'Shea, Projects in Optics. Applications Workbook
R.Bruman, Exploritorium Cookbook I (The Exploratorium, San Francisco, 1984)
R.Hipschman, Exploritoriuni Cookbook II (The Exploratorium, San Francisco, 1980)
R.Hipschman, Exploritorium Cookbook III (The Exploratorium, San Francisco, 1987)
H.F.Meiners, edt Physics Demonstration Experiments (American Association of Physics Teachers, 1970)
R.Ehrlich, Turning the World Inside Out ( Princeton University Press, Princeton, NJ, 1990) 2l6pp
H.Daniel, Demonstratiusversude aus der Optik (Musterschmidt-Verlag Gottingen, 1960)
M.Francon, M.Krauzman, J.P.Mathieu, M.May, Experiments in Physical Optics (Gordon & Breach,
New York, 1970) 27lpp
M.Francon, Experiments d'Optique Physique (Gordon & Beach, New York, 1969) 249pp
R.W.Pohl, Optik und Atomphysik (Springer-Verlag, Berlin, 1967) 34'7pp
Popular Optics (Edmund Scientific, No 9445, 1974)
Unesco, 700 Science Experimentsfor Everyone (Doubleday, New York, 1958)
E.Edser, Lightfor Students (Macmillan, London, 1902)
W.A.Hilton, Experiments in Optical Physics (Hilton, Liberty, MO, 1974)
Demonstration Experiments ofBasic Phenomena in Optics (American Optical, Southbridge, MA, 1968)
A.F.Wagner, Experimental Optics (Wiley, New York 1929) 2O3pp
H.A.Robinson, ed, Lecture Demonstrations in Physics Translated from Russian by K.V.Robinson,
(American Institute of Physics, 1963; University Microfilms, 1976, number OP-23512 $140) 473pp
J.A.Davis, "Resource Letter PhD-i : Physics demonstrations" American Journal of Physics, v 47, p 835
(1979)
Laser specific
T.Kallard, Exploring Laser Light (Optosonic Press, 1977) Reprinted by the AAPT
H.H.Gottlieb Experiments Using a Helium-Neon Laser (Metrologic, Belmawr, NJ, 1974)
Experiments in Physical Optics Using Continuous Laser Light Educational Series No.1. Optics
Technology, Inc.
R.S.Sirohi, A Course ofExperiments with He-Ne Laser (Wiley, New York, 1985) lO3pp
F.McAleese, The Laser Experiments Handbook (McGraw-Hill, New York, 1979)
G.Wnght, G.E.Foxcroft, Elementary Experiments with Lasers (Wykham, 1973)
G.L.Rogers, Hand Book ofGas Laser Experiments (Illifee Books Ltd, London, 1970)
R.Pantell, Experiments in Optics with a Laser Source (Optics Technology mc, 1969)
Kid books
B.Taylor, Bouncing and Bending Light (Franklin Watts, New York, 1990) 32pp
B.Taylor, Color and Light - Fun with Simple Science (Warwick, New York, 1991) 4Opp
B.Murphy, Experiemnts with Light (Lerner, Minneapolis, 1991) 32pp
N.Ardley, The Science Book ofLight (Gulliver, San Diego, 1991) 29pp
R.Gardner, Investigate and Discover Light A Franklin Institute Science Museum Book
(Julian Messner, Englewood Cliffs, NJ, 1991) l37pp
The Magic Mirror, An Antique Optical Toy (Dover, New York, 1979)
C.B.Grafton, Optical Designs in Motion with Moire Overlays (Dover, New York, 1976)
F.J.Moore, The Magic Moving Alphabet Book (Dover, New York, 1978)
F.J.Moore, The Incredible Moving Picture Book (Dover, New York, 1987)
SPIE Vol. 2525 / 19
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