lecdem.physics.umd.edu

PHYS270

L6-04: OPTICAL BOARD - RAY DIAGRAM - REAL IMAGE POS LENS

L6-04

Use principal rays to locate a real image produced by a convex lens.

The central ray passing through a half-silvered mirror serves as the optic axis, and the vertical ray between the two mirrors serves as the object arrow. By rotating the mirror at the tip of the arrow the three principal rays (or other rays) can be produced, all of which intersect at the image point (arrow tip). The focal points of the lens, about 17" (43cm) from the lens surface, can be indicated using squares of masking tape or black tape. A single converging lens in front of the object is used to keep the ray narrow. The object must be close to the left side of the optical board to keep the image (inverted arrow at far right) on the board.
L6-08: REAL IMAGE OF CONVERGING LENS - LIGHT BULB

L6-08

Show the real image of a converging lens.

An incandescent bulb with printing on the top is used as an object to be imaged with lenses of different focal lengths. Hold the lens above the light bulb at a distance slightly greater than the focal length of the lens to cast an image of the trademark onto the ceiling. Change lenses to change the magnification. (10cm and 20cm focal length lenses tend to work best in most rooms, but 5cm, 30cm, and possibly others can also be available upon request.)

OM1, LS1
L6-09: REAL IMAGE OF CONVERGING LENS

L6-09

Show the systematics of real image formation by a converging lens.

An arrow/disc object baffle lit from behind by a bright point source of light is used as the object, and various convex lenses are used to cast images of the key onto a screen. The effect of variation in focal length and object distance can be readily seen. Lenses with 10cm, 20cm, and 30cm focal length are provided.

Combinations of two convex lenses or a concave and a convex lens used together can also be demonstrated. Please request additional lenses if desired.
L6-12 MAGNIFYING LENS IN WATER

L6-12

Shows that focal properties of a lens depend on the medium in which the lens is located

A small fuse box is mounted on a holder at a distance less than the focal length behind a convex lens, so the lens acts as a magnifying glass. Note, in the photo at the left, the magnification of the fuse box when the system is in air. Then dip the entire lens-object system into water. Because there is much less bending of the light at the water-glass interfaces than at the air-glass interfaces, the magnification is much less

L6, L4

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M1-01: LASER DIFFRACTION - FIXED SINGLE SLIT

M1-01

Demonstrate single slit diffraction.

Position single slit in holder on cross-carriage in laser beam to obtain diffraction. Pattern can be shown on a distant screen, or the small screen shown in the picture. Magnification with the cylindrical lens can be used as necessary. One slide with four slits is available: 0.2mm, 0.04mm, 0.08mm, and 0.16mm, as well as individual slides of 0.12mm, 0.25mm, and 0.5mm.

FS1
M1-02 LASER DIFFRACTION - VARIABLE SINGLE SLIT

M1-02

Demonstrates single slit diffraction

Position single slit in holder on cross-carriage in laser beam to obtain diffraction. Pattern can be shown on a distant screen, or the small screen shown in the picture. Magnification with the cylindrical lens can be used as necessary. One slide with four slits is available: 0.2mm, 0.04mm, 0.08mm, and 0.16mm, as well as individual slides of 0.12mm, 0.25mm, and 0.5mm

FS1
M1-04: LASER DIFFRACTION - WIRES

M1-04

Show diffraction by wires of different size.

Position the three-wire slide in a holder on the cross-carriage in the laser beam to see the diffraction pattern. The pattern can be viewed directly on a distant screen or on the small screen on the laser cart, with use of the cylindrical magnifying lens if appropriate.

FS1

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M1-06: LASER DIFFRACTION - HUMAN HAIR

M1-06

Demonstrate laser diffraction with a human hair.

Shining a laser across a human hair (mounted in a projectual, shown at left above) creates a characteristic diffraction pattern.
M1-11 LASER DIFFRACTION - FIXED DOUBLE SLITS

M1-11

Demonstrates double slit interference

A slide containing four sets of double slits is positioned in the laser beam using a slide holder on a cross-carriage mount. Any of the four sets of slides can easily be slid into the beam. The slits are available in two different widths with tow different separations. Challenge your students to predict how the relationship of slit width and slit spacing will affect the interference pattern created.
Background

Collimated light waves come from the laser and pass through a pair of narrow slits in the slide; the light passes through and then projects on the distant screen. But light travels as an electromagnetic wave, so when the light comes out of the two slits, it forms two wavefronts, just like ripples from two stones dropped in a pond. These two wavefronts can interfere with each other, as we can model with this pair of overlapping concentric circles. Where two peaks or two valleys of the wave pattern line up, they add together, interfering constructively; when a peak and a valley overlap, they cancel out, interfering destructively. The same happens with light waves; the light from the two slits overlaps, and creates a pattern of bright spots (constructive interference) and dark spots (destructive interference). The spacing between the bright and dark fringes ultimately depends on three things: the distance between the slits and the screen, the wavelength of the light, and the spacing between the two slits.
Two simulations that can be of value in introducing this topic:
• a ripple tank simulation here in the Physlet Physics collection at AAPT’s compadre.org: https://www.compadre.org/Physlets/optics/prob37_7.cfm Use your mouse to measure the positions of the peaks relative to the double slit at the base of the image.
• this PhET Simulation at the University of Colorado: https://phet.colorado.edu/sims/cheerpj/quantum-wave-interference/latest/quantum-wave-interference.html Use the button on the right to activate the double slit barrier.

FS1
M1-34: LASER DIFFRACTION - COMPACT DISC

M1-34

Demonstrate interference of a laser beam by a type of grating.

This demonstration uses a compact disc recording to produce an interference pattern with a laser beam. Hold the CD at an angle with respect to the incoming laser beam and look for the diffraction pattern on the wall or the ceiling. Note that the angle must be reasonably large because the spacing of the spiral "groove" on the disc is 1.6 microns, only about twice the wavelength of the laser light. You will see both the interference pattern and specular reflection off the shiny surface of the dics.
M1-35: LASER DIFFRACTION - VIDEODISC

M1-35

Demonstrate diffraction of a laser beam by a standard videodisc.

A standard videodisc has very small "line" spacing, so it produces a diffraction pattern that has very large spacing between the diffraction maxima, as seen in the photograph above.
M2-01 LASER DIFFRACTION - PINHOLES

M2-01

Demonstrates laser diffraction by pinholes

A series of pinholes is mounted on a slide which can be moved across the laser beam on a cross-carriage. Pinhole sizes include: 1.0mm, 0.8mm, 0.6mm, 0.4mm, 0.2mm, and 0.1mm. The pattern can generally be seen in the lecture hall without aid of a magnifying lens by backing the cart as far as possible away from the screen in front of the hall. For display on the small screen on the cart optical rail a spherical lens can be used if necessary.

FS0
M2-02: LASER DIFFRACTION - OPAQUE DISCS

M2-02

Demonstrate laser diffraction by opaque discs.

A set of opaque discs is mounted on a slides which can be moved across the laser beam on a cross-carriage. Two sets of opaque discs are available: (1) 0.25mm, 0.50mm, and 1.00mm, and (2) 0.50mm, 1.00mm, and 1.50mm. The smaller discs allow more laser light to pass around them and therefore produce a brighter pattern. The pattern can generally be seen in the lecture hall without aid of a magnifying lens by backing the cart as far as possible away from the screen in front of the hall. For display on the small screen on the cart optical rail a spherical lens can be used if necessary.
M3-01 MICHELSON INTERFEROMETER - LASER LIGHT

M3-01

Shows laser light fringes using a Michelson interferometer

This experiment uses the laser and white light combination Michelson interferometer setup. The laser light is expanded by a 2 cm focal length convex lens and reflected into the interferometer by a front surface plane mirror. Either circular or straight line fringes can be displayed by adjusting the tilting mirror. The light exiting the interferometer is focused onto a distant screen, providing a field about one foot in diameter, clearly visible over the entire lecture hall.

FS1
M3-02: MICHELSON INTERFEROMETER - WHITE LIGHT

M2-02

Show white light fringes using a Michelson interferometer.

This experiment uses the laser and white light combination Michelson interferometer setup. Because alignment requires a laser, this demonstration will be delivered (and can be used) with a laser installed. White light from a bright point source is collimated by a condenser lens and passes through a heat filter directly into the interferometer. The light exiting the interferometer is focused onto a distant screen, providing a field about one foot in diameter, clearly visible over the entire lecture hall. The fringe colors can be seen to be negative colors, that is, complementary colors to the colors to the spectral colors which are eliminated by destructive interference.

The photographs above show some of the color patterns using this interferometer.

This demonstration is very sensitive to alignment and temperature, and is not recommended for routine classroom use.

FS1
M3-42: FABRY-PEROT INTERFEROMETER - SODIUM LIGHT

M3-42

Sodium light interference with Fabry-Perot interferometer.

Using sodium light a nice circular interference pattern can be obtained, which can be effectively viewed with the TV camera zoom lens. The Fabry-Perot interferometer can resolve the sodium doublet.
M4-02: NEWTON'S RINGS - PROJECTION

M4-02

Demonstrate a well-known interference pattern

A high-intensity mercury lamp illuminates a pair of touching glass surfaces, one plane and the other convex, contacting each other along the central ray. The reflected light is focused onto a distant screen, forming the classical Newton's rings interference pattern.
M5-03: LASER DIFFRACTION - OPTICAL CRYSTALS

M5-03

Two dimensional diffraction patterns with crystal symmetries.

These optical crystals consist of simple arrays of various shaped diffraction centers arranged with several two dimensional symmetries. Diffraction by such a crystal produces a pattern with the symmetry of the scattering slide. Winner of the 1973 AAPT apparatus competition.
M5-04: LASER DIFFRACTION - EXOTIC ARRAYS

M5-04

Show diffraction by arrays of complex figures.

Twelve slides are used with a laser to produce diffraction patterns from complex-shaped arrays of apertures and/or obstacles. Plates are: (1) double slits, (2) multiple slits, (3) slit to square transition, (4) random and regular arrays of dot apertures, (5) Babinet's principle with circular apertures and obstacles, (6) Babinet's principle using + signs, (7) Babinet's principle with quad slits of different spacings, (8) fun patterns, obscured apertures in random array, (9) random circular obstacles - 0.20mm diameter, (10) random circular obstacles - 0.10mm diameter, (11) random circular apertures - 0.10mm diameter. Examples are given in the photographs below; the dynamic range of the camera limits the intensity range much more severely than your eye.
M6-01: HOLOGRAM - LASER LIGHT - VOLKSWAGEN

M6-01

View a laser light hologram.

The hologram, in the form of a slowly rotating cylinder, is illuminated from inside as illustrated by either a white light with a red plastic filter (photograph in center) or a laser light scattered by a piece of wax paper (photograph at right). The laser light renders better resolution of the hologram details, but this is obscured in the photograph by the laser speckle.

M6, LS1