t(i + j) »» i cos t + j sin t »» cos t(i - j).Various Light Sources -- a collection of show and tell light sources from candles and carbon arcs to noble-gas discharge lamps and LED's.
Straight Line Propagation -- cast shadow of hand, etc. from a carbon arc lamp without a lens, and/or show laser beam through chalk dust cloud.
Pinhole Camera Effect -- large crude but workable pinhole camera projects the image of a lamp filament onto a translucent screen.
Inverse Square Law -- light from a pinpoint light source proces current from a small solar cell module, which is attached to and drives a vertical LED bar-graph display. The solar cell/display is placed a known distance (call it r) from the light source and the reading on the bar-graph is noted. The sensor/display is then drawn away from the light source to distances of 2r and 3r, where display readings of approximately 1/4th and 1/9th the original reading are observed. Moving the sensor/display smoothly away from the light source “graphs out” the 1/r2 dependence of light intensity on distance from the source.
Siren in Vacuum -- a small electronic siren equipped with a flashing LED is mounted inside a bell jar. The siren is turned on and it is noted that the LED flashes in time with the beeping. The air is then evacuated from the jar, and although the flashing LED can still be seen, no sound can be heard from the siren. Shows that light, unlike sound, requires no medium for propagation.
Infrared in Spectrum w /Thermopile (Planck Curve) -- light from a hot carbon arc is spread into a spectrum, then various portions of the spectrum are scanned with a thermopile. It is shown that the greatest amount of energy is in the infrared portion of the spectrum where no visible light exists, then tapers off into the visible and disappears in the ultraviolet. A new thermopile that drives a vertical LED display can be used to graph out the spectral emission curve for the carbon arc.
Ultraviolet in Spectrum -- light from an arc lamp is spread into a spectrum, and a fluorescent sheet placed beyond the violet end of the spectrum fluoresces where no visible light exists.
Wavelike Properties (see Arago's Bright Spot) -- Arago's bright spot appearing in the middle of the shadow of a sphere shows the wavelike diffraction of light. Can also do shadows of point and eye of needle. Can be viewed individually by students or projected using a video camera.
Photoelectric Effect (electroscope) -- bright light from an arc lamp strikes a metal plate mounted atop a negatively charged electroscope. Scope discharges quickly if the plate is zinc, less quickly for aluminum or copper. Will not discharge if a plate of glass is held between the light and the zinc (cuts out UV), or if the electroscope is positively charged.
Fluorescence -- various fluorescent materials are available for viewing under ultraviolet light, including natural minerals, man-made objects, liquids, and paints.
Luminescence -- a luminescent rubber ball, skeleton etc. which may be charged up by normal (or UV) light for a glow-in-the-dark effect.
Shadow Sheet -- a luminscent sheet that can be charged up by the from a camera flash unit. Put your hand in the way of the flash and a “shadow” of your hand will appear on the sheet. Also has a small “pen” light source that can be used to write (temporarily) on the sheet.
Chemiluminescence -- one of those chemical light sticks. Break the vial inside and as the two chemicals mix they emit a green glow.
Light Meter -- electronic photometers, one with digital and one with analog output.
Angle of Incidence/Reflection -- light beam falls on a mirror mounted on a large rotating protractor. Various angles of incidence and reflection can be compared to show that I=R.
Location of Image (candle in glass of water) -- a vertical glass window pane stands between two objects - a candle in front and a beaker of water in the rear at the position of the candle's image in the glass. The image of the candle appears to be burning under water. The entire stand can be rotated to show that the position of the candle's image relative to the glass does not change with different viewing angles.
Diffuse/Specular Reflection -- reflect white light or laser off a rough surface to show diffuse reflection. Compare with mirror, metal surface, etc.
Hinged Mirrors (multiple reflections) -- two plane mirrors are joined with a hinge and can be adjusted to various angles. A small flashlight bulb mounted between the mirrors is the object, and the number and positions of its images are noted as the angle between the mirrors changes.
“Barbershop Mirror” Effect -- two plane mirrors are placed parallel to and facing one another. An object is placed between them and multiple images are seen in the view past the edges of the front mirror.
Beer Sign -- a commercial sign using the 'Barbershop Mirror' effect. Beer logo is placed between two mirrors, the front mirror being partially transparent. Some of the light bouncing between the mirrors escapes through the front mirror, and multiple images of the logo are seen.
Image Reversal (DIXIE/SOUTH) -- two words which mean the same are viewed normally and in a mirror. DIXIE has mirror symmetry along the horizontal axis and appears unchanged in the mirror, but SOUTH looks quite different. Also CHECK/THIS.
Image Perversion (TIME/EMIT) --the word “TIME” is printed on a clear sheet of acrylic which is backed with an opaque sheet of cardboard. When you turn it around to face the mirror, the students will see that the word is reversed left-to-right (“EMIT” with a backwards E). Many students think that the mirror has reversed the word left-to-right. Pull the cardbord off and they will see that the image has the same left-to-right orientationas the original - you reversed it left-to-right when you turned it around. A rubber-tipped arrow stuck on the back of the acrylic will show how mirrors truly reverse images: along an axis at right angles to the mirror’s surface.
Parity Reversal -- two ball-and-stick figures of opposite “handedness” are used with a plane mirror to show parity reversal of reflected images.
Corner Reflector -- three plane mirrors joined to form the corner of a cube. This has retroreflecting properties, and is similar to the reflectors left on the moon for laser distance determinations and the reflectors in those brightly reflecting roadway lane dividers.
Refraction and Reflection from Plastic Block -- a large rectangular acrylic block on the optics board (see above) will refract and partially reflect incident beams. Can be rotated to various angles to vary the angle of incidence/refraction).
Refraction from Water Tank -- stick in a tank of water appears “broken”.
Lead Glass Slab -- a large lead glass slab with a refractive index of approximately 2 shows strong refraction, dislocation of a transmitted image of a stick.
Acrylic/Lead Glass Comparison -- same setup as above, but with an acrylic panel of equal thickness atop the lead glass for comparison of refractive properties.
Apparent Depth -- the lead glass and acrylic blocks mentioned above, when viewed from an angle, demonstrate the apparent depth effect. The edge which is viewed directly shows the true depth of the blocks; the edge viewed through the blocks appears shorter, or closer to the surface.
Critical Angle and Total Internal Reflection -- a parallel beam of light traveling underwater is reflected up to the water/air interface by a small mirror. The mirror may be rotated to change the angle of incidence. Fluoroscein in the water and a thread screen above the water allow the incident, refracted, and reflected beams to be seen clearly. As the angle of incidence reaches the critical angle, the refracted beam is seen to skim just over the surface of the water. Increase the angle slightly from that, and the refracted beam disappears while the reflected beam jumps in intensity (total internal reflection)
Light Pipe -- curved lucite rod transmits laser beam, etc.
Fiber Optics -- small fibers transmit laser, white light.
Concave and Convex Mirrors -- uses either the optics board or thread screen (see above) to trace incident and reflected rays from curved mirrors. A greater variety of mirrors is available for the thread screen.
Large Concave Mirror:
Strawberry -- real image of plastic strawberries placed in front of the mirror.
Candle Burning at Both Ends -- a burning candle placed slightly above the center of curvature of the mirror has a real image of the flame at its bottom - it appears to be burning on both ends.
One Candle Searchlight -- burning candle placed at the focus of the mirror throws a roughly parallel beam to the far wall.
Magnification -- a backlit black-and-white grid and a large (12 in.) lens are used to demonstrate magnification by convex lenses. Also good for showing spherical and chromatic aberrations.
Image Formation -- light from a backlit “object” is focused by a convex lens onto a translucent screen. Image reversal and magnification can be shown.
Conjugate Focal Positions -- the above arrangement is used to show that there are two lens positions which will form an image on the screen.
Ray Tracing with Lenses -- concave and convex lens on the optics board or thread screen show the basic properties of lenses, ray tracing, etc.
Fillable Air Lenses -- air-filled lenses held under water in a parallel beam of light show “reverse” refraction in going from a higher to a lower index of refraction. Concave lens focuses beam, etc. Removing your finger from the top of the handle tube allows the lens to fill with water, so that the medium of the lens is the same as the surroundings and the parallel beam of light passes through without effect. Remove the water-filled lens thus formed from the optics tank and insert it in the thread screen to show that its focusing properties are now the opposite of the original air-filled lens.
Glass Lenses in Air/Water -- a lens is inserted in the thread screen to show the focal length, then is dipped into the optics tank to show a much longer focal length in water due to the greater refractive index of the medium. Can also be done with the optics tank half-full to show both focii simultaneously.
Spherical Aberration -- shows different points of focus for different areas of a large plano-convex lens. First the outer half of the lens is blocked off, and an image is brought to focus using the lens. Then the inner half is blocked off, and the image is seen to be out of focus. The image can now be brought back to focus by moving the lens. The image formed by the outer half of the lens is seen to be fuzzier than that formed by the inner half.
Chromatic Aberration -- shows different points of focus for red and blue light through a large plano-convex lens. Can also show colored halo around focused white light.
Achromatic Pair -- shows correction of chromatic aberration using a correcting lens.
Artificial Rainbow (Water Flask) -- a round flask filled with water simulates a raindrop, casting a small rainbow on the screen when illuminated with a carbon arc.
Rainbow (Glass Beads) -- a point source of light situated above a black velvet board covered with tiny glass beads creates a rainbow.
Cylindrical Lens -- shows properties of a cylindrical lens.
Inverting (Galilean) Telescope -- a working model through which students can observe the inverted image of a clock on the far wall.
Noninverting Telescope -- similar to the Galilean scope, but with a concave lens for the eyepiece; shows an upright image.
Reflecting Telescope -- simple off-axis Newtonian reflector gives an upright image of the old clock on the wall.
Projection Microscope -- a self-contained projection microscope magnifies the grids from two fine wire mesh screens.
Microscope Chart -- chart showing the components of a microscope.
Zoom Lens -- a slide projector so equipped.
Slide Projector (Disassembleable) -- a 3 x 4 inch slide projector which is easily disassembled to show innards.
Eye Defects -- overhead transparency shows the optical causes of various eye defects.
Film Loops:
- Resolving Power
Single Slit (Variable Width) -- a variable-width single slit shows diffraction of a laser beam.
Cornell Slides (Single, Double, and Multiple Slits) -- a slide containing single slits of different widths, double slits of different separations, and multiple slits with various numbers of slits per centimeter.
Aperture (Airy Disk) -- projected circular diffraction pattern from passing a laser beam through a small aperture.
Knife Edge -- a projected edge diffraction pattern using a razor blade, laser, and lens.
Arago's Bright Spot -- bright spot in the center of the shadow of a small sphere. Can be viewed individually at class change or projected from a video camera.
Point and Eye of Needle -- Individually viewed diffraction pattern of light around and through eye and point of a needle.
Crossed Slits -- a pair of multiple slits at right angles diffracts laser light into a two-dimensional pattern.
Point Source and Wire Mesh -- a point source of white light is viewed through small pieces of wire mesh handed out to the students. The weave of the mesh is fine enough to diffract the light strongly.
Hair or Thin Wire -- projected diffraction pattern from a thin wire in a laser beam.
Ripple Tank -- projected diffraction pattern of water waves through slits.
Diffraction with Feather -- a laser beam passing through the closely-spaced hairs of a feather will spread into a diffraction pattern on the screen.
Film Loops:
- Diffraction - Single Slit (Light)
- Single Slit Diffraction (Ripple Tank)
- Diffraction - Double Slit (RT)
- Multiple Slit Diffraction (RT)
- Shadow of a Hole (Light)
- Diffraction and Scattering Around Obstacles (RT)
Slits:
Double Slit -- projected interference pattern using a double slit and a laser. Slit separation may be varied, either continuously or in known steps.
Multiple Slits -- same as above with multiple slits, various numbers of slits per centimeter.
Ripple Tank -- a two “slit” barrier produces an interference pattern.
Gratings:
Transmission Gratings -- three different ruling widths are available for use with white light or a laser.
Reflection Gratings -- concave reflection gratings can simultaneously disperse and focus white light.
Two-dimensional Grating -- produces a two-dimensional pattern with white or laser light.
Thin Films:
Pohl's Mica Sheet -- violet light from a mercury arc is reflected from a thin sheet of mica onto a screen to produce a circular interference pattern from the interference of reflections from the front and back surfaces of the mica.
Soap Film -- white light is reflected off a thin soap film onto a screen. Dazzling multicolor interference patterns are formed, with rough bands of different colors indicating the varying thickness of the film. Eventually a dark area forms at the top (where the film is less than a quarter wavelength thick), spreads down throughout the pattern, and the film pops.
Newton's Rings -- white light projection of interference patterns from a thin layer of air between two layers of glass; one flat and the other curved but nearly flat. A concentric circular interference pattern is obtained which can be varied by squeezing the plates of glass.
Glass Plates in Sodium Light -- two large flat glass plates are stacked and illuminated by a sodium lamp. The yellow and black interference fringes are easily visible to the entire class.
Interference Filters -- thin film layers of various thicknesses on glass are inserted in the thread screen to demonstrate their effect upon a beam of white light. Both reflected and transmitted colors can be seen simultaneously, and the reflected color is seen to be different than the transmitted color. Changing the angle of incidence changes the colors.
Michelson -- projected fringes may be shifted by moving the mirrors.
Microwave -- interference fringes from microwaves are heard as varying output from the audible power indicator of the microwave generator as the 'mirrors' are moved.
Holograms -- a variety of holograms are available for individual viewing in a laser beam or white light. A video camera allows for whole-class viewing if desired.
Film Loops:
- Diffraction, Double Slit
- Michelson Interferometer
Slotted Boxes -- a rope passes through slots on wooden boxes which can be horizontal or vertical. Wiggle the rope and the first box “polarizes” the wave. The wave will either stop at the second box or pass through, depending on whether the slot is crossed or parallel to the first.
Vector Models -- dowel rod models for plane and circular polarization.
Polaroid Sheets -- 12" x 12" sheets of Polaroid material for use on the overhead projector.
Polarization by Reflection (Polaroid Sheet) -- a beam of white light reflects off a glass plate and appears on the wall. Interpose a Polaroid sheet and rotate it to show that the reflected beam is polarized. Do the same with the beam shining straight onto the wall to show that the unreflected beam is not polarized.
Brewster's Angle -- uses the above setup to show that there is an optimum angle of reflection for maximum polarization of the beam.
Polarization by Reflection (Double Reflection) -- a parallel beam light source mounted on the edge of a rotation stand strikes a glass plate mounted at the center of the stand and is reflected up along the axis of rotation. the beam then strikes a second glass plate and is reflected onto a translucent screen. The spot of light will be either bright or dim depending on the relative angle between the two glass plates as the stand is rotated through a full turn or more. Polarization state of the transmitted beams may also be checked, using a polaroid sheet.
Polarization by Scattering -- a light beam passes through a Polaroid analyzer, then is scattered by passage through a tank of water with a little powdered milk added. The polarized light is scattered preferentially in the direction of its polarization, and by rotating the analyzer the direction of most intense scattered light can be varied. A mirror atop the tank allows simultaneous viewing of top and front views for comparison of vertically and horizontally scattered light.
Flake Mica -- demonstrates the polarizing capability of thin flakes of mica.
Polarization by Double Refraction -- a small beam of light passes through a calcite crystal, is doubly refracted, and is projected on a screen as two dots. Rotating a Polaroid analyzer atop the crystal makes the dots appear and disappear in alternation, showing that the beams are polarized perpendicular to one another. Rotating the crystal makes one dot revolve around the other.
Nichol Prism -- light passes through two calcite prisms with an air gap between them. The light is doubly refracted by the calcite, and the arrangement of the prisms is such that the extraordinary ray is totally internally reflected at the prism/air interface, while the ordinary ray slips through to the second prism and escapes to be observed. Since the two rays are perpendicularly polarized, the emerging ray is polarized (use with overhead projector).
Polarization of Microwaves -- polarized microwaves pass through a metal grating; the orientation of the grating (vertical or horizontal) greatly affects the intensity of the transmitted beam.
Sugar Tube -- light passes through a flask of sugar solution (corn syrup) sitting between two Polaroid sheets on the overhead. Adding more syrup increases the path length, changing the transmitted color due to increased optical rotation.
Barbershop Sugar Tube -- a long vertical tube containing a strong sugar solution has a beam of polarized white light entering from the bottom. The sugar rotates the different colors in the beam different amounts as the light passes through the tube, and the light scattered out at any point will be different colors in different parts of the tube, creating a colored barbershop-pole effect.
Circular Polarizer -- a sheet of Polaroid laminated to a quarter-wave sheet with the characteristic direction of the polaroid sheet at 45° to the exceptional direction of the quarter wave sheet. When the sheet is placed on a mirror with the Polaroid side away from the mirror, the following occurs: unpolarized light incident on the sheet is first plane polarized by the Polaroid sheet and then circularly polarized by the quarter wave sheet (the two orthogonal components defined by the exceptional direction of the sheet have relative phase 90°). The light is then reflected by the mirror and passes back through the quarter wave sheet, picking up another 90° of relative phase between the two components. The resulting light is once again plane polarized, but at right angles to the original direction and thus cannot pass back through the Polaroid sheet - the mirror looks black (the sequence is:
t(i + j) »» i cos t + j sin t »» cos t(i - j).Photoelastic Strain Figures -- transparent plastic shapes are held between two crossed Polaroid sheets and squeezed. Light passing through the plastic is optically rotated, the amount depending on color and stress level in the plastic; different colors thus represent different stress levels.
Acetamide Crystals -- crystals are placed between two crossed Polaroid sheets, melted with a hot air gun, then allowed to cool. As the crystals solidify, the emerging strain patterns are seen as colored bands.
Faraday Effect -- intense magnetic field around a tube filled with optically active solution changes the degree of rotation of a polarized beam.
Kerr Effect -- electric field around an optically active solution changes the degree of rotation of a polarized beam.
Continuous Spectrum -- rainbow white light spectrum from reflection or transmission gratings.
Infrared in Spectrum w /Thermopile (Planck Curve) -- light from a hot carbon arc is spread into a spectrum, then various portions of the spectrum are scanned with a thermopile. It is shown that the greatest amount of energy is in the infrared portion of the spectrum where no visible light exists, then tapers off into the visible and disappears in the ultraviolet. A new thermopile that drives a vertical LED display can be used to graph out the spectral emission curve for the carbon arc.
Ultraviolet in Spectrum -- light from an arc lamp is spread into a spectrum, and a fluorescent sheet placed beyond the violet end of the spectrum fluoresces where no visible light exists.
Line Spectra -- hydrogen, neon, mercury, and helium emission tubes are examined with transmission gratings which are handed out to the students. The sources are arranged in a vertical stack and operate simultaneously, so that all four spectra are seen at once. A white light atop the stack may be turned on separately to compare a continuous spectrum with the four quantized emission spectra.
Absorption by Sodium Vapor -- a salt-soaked stainless steel screen is held in a flame in front of two backlit screens; one lit by white light and the other by sodium light. In front of the white light screen, the flame is transparent and faintly yellow. In front of the yellow sodium light screen, the flame appears black.
Absorption Spectrum of Neophan Glass -- a sheet of neophan glass inserted into a continuous spectrum demonstrates broad absorption lines in the yellow and green areas of the spectrum (used to cut out sodium emission glare from hot glass).
Fluorescence -- various fluorescent materials absorb ultraviolet light and emit various colors of visible light.
Luminescence --various glow-in-the-dark items that are excited by visible or UV light.
Shadow Screen --a luminescent screen that comes with a camera-type flash. Put your hans against the screen and flash the lamp; the screen will glow except for a “shadow” where your hand was. A light pen also allows drawing lines on the screen.
Film Loops:
- Absorption Spectra
Additive Color Mixing Box -- a box containing red, blue, and green light sources with individual brightness controls shows aspects of additive color mixing, primary and secondary colors, etc.
Subtractive Color Mixing -- colored filters are stacked on the overhead to show subtractive color mixing.
Color Computer -- commercial color mixing tool shows the effect of mixing various (absorptive) colors.
Filters -- various color filters used with white light.
Recombined Spectrum -- a continuous spectrum from a prism is recombined into white light with a second prism.
Newton Color Disk -- disk sectioned into primary colors “smears” into white when rotated.
Spinning B/W Disks -- illusion of color on a spinning black and white disk due to the eye's different reaction speeds to different colors.
Colored Objects in Spectrum -- objects colored with fairly pure hues are moved through a white light spectrum to show reflectivity and apparent color in different colors of light.
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