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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Geometrical Optics
  video  - Interference and Diffraction
 Arago's (Poisson's) Spot
 Razor Edge Diffraction
 The Eye

Arago's (Poisson's) Spot


A non-intuitive illustration of the wave theory of light.


Point the setup at the screen (the farther away from the screen, the better). Note that the green laser has a beam expander on it. Therefore, place your "second" lens at the focus of the laser beam to minimize effects of lens abberation, since at the focus one minimizes the area the light projects on the lens.


The razor edge and the Poisson spot are on the same mount. We have used 188mm or -20cm lens.
In room 203 use a regular camera and #4 light setup to project the diffraction pattern on the big screen.


  • Small Bead on Glass Plate
  • Optical Stand
  • Laser
  • 18.8 cm Lens and stand