Monday, 22 July 2013 10:51

## M1-11 LASER DIFFRACTION - FIXED DOUBLE SLITS

• ID Code: M1-11
• Purpose: Demonstrates double slit interference
• Description:
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.
• Availability: Available
• Loc codes: FS1
• #### M1-01: LASER DIFFRACTION - FIXED SINGLE SLIT

Demonstrate single slit diffraction. Read More
• #### M1-02 LASER DIFFRACTION - VARIABLE SINGLE SLIT

Demonstrates single slit diffraction Read More
• #### M1-04: LASER DIFFRACTION - WIRES

Show diffraction by wires of different size. Read More
• #### M1-05: FINGERS AND SODIUM SOURCE - VARIABLE SINGLE SLIT

See single slit diffraction. Read More
• #### M1-06: LASER DIFFRACTION - HUMAN HAIR

Demonstrate laser diffraction with a human hair. Read More
• #### M1-11 LASER DIFFRACTION - FIXED DOUBLE SLITS

Demonstrates double slit interference Read More
• #### M1-12: INTERFERENCE - TRANSPARENCIES

Analog to the interference pattern from two identical light sources. Read More
• #### M1-13: INTERFERENCE - KLINGER TRANSPARENT SLIDES

Model interference between two point sources. Read More
• #### M1-14: MICROWAVES - INTERFERENCE OF TWO POINT SOURCES

Demonstrate interference using microwaves. Read More
• #### M1-15: MICROWAVES - YOUNG'S DOUBLE SLIT INTERFERENCE

Illustrate two-slit interference using microwaves. Read More
• #### M1-16: INTERFERENCE OF LIGHT - SOUND WAVE MODEL

Show explicitly how two waves with the same amplitude and frequency will interfere when their relative phase changes. Read More
• #### M1-21: LASER DIFFRACTION - MULTIPLE SLITS

Show the transition from one slit to multiple slits and the diffraction grating. Read More
• #### M1-22: LASER DIFFRACTION - GRATINGS

Demonstrate diffraction (well, actually interference) by a grating. Read More
• #### M1-32: SLITFILMS AND LONG FILAMENT BULB

Diffraction and interference by various slits and combinations of slits. Read More
• #### M1-33: LASER DIFFFRACTION - PHONOGRAPH RECORD

Demonstrate interference of a laser beam by a type of grating. Read More
• #### M1-34: LASER DIFFRACTION - COMPACT DISC

Demonstrate interference of a laser beam by a type of grating. Read More
• #### M1-35: LASER DIFFRACTION - VIDEODISC

Demonstrate diffraction of a laser beam by a standard videodisc. Read More
• #### M1-41: PEACOCK FEATHER

Demonstrate a type of iridescence. Read More
• #### M1-42: IRIDESCENT GREEN JUNE BEETLE

Demonstrate a type of iridescence. Read More
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