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PHYS273

  • K8-45 RADIO WAVES FROM SPARK

    K8-45
    Demonstrates that a spark contains radio waves
    Turn the radio on to a frequency where there is no station. Hold the battery near the radio and short it out by quickly contacting and releasing the contact using a banana wire cable. A clicking sound will readily be heard on the radio.

    Compare J3-23: Faraday Cage - Radio Waves, which can use the same radio to illustrate a related phenomenon.
    K8

  • K8-46: Radio Waves & Faraday Cage

    K8-46
    Demonstrates that radio waves do not penetrate a Faraday cage
    Tune the radio to an inoffensive station audible in the classroom. Then place the radio on a metal surface; the radio continues to play. Show students the cage and ask what will happen if you lower the cage over the radio. Note that they can still see through the cage, so light is passing through.

    Lower the cage over the radio. Once the cage surrounds the radio completely, it prevents RF waves from passing through, silencing the radio. This also shows the wavelength dependence of a Faraday cage; the much shorter wavelengths of the electromagnetic waves of visible light pass through the openings unhindered.
    K8

  • 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

    m1-01b

     

  • 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

  • M1-11 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