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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
 Additive Color Mixing
 Line (discontinuous) Spectra
 Rainbow II
  video  - Sunset
 The Eye

 video  - Sunset


A simulated sunset demonstration which shows the wavelength dependence of the relative intensity of scattered light from microscopic particles.


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Dissolve 10g of Sodium Thiosulfate in 1L of water (at room temperature) in a 1000mL beaker. Fill a second 1000mL beaker with pure water. Place both beakers on the overhead and center them each on a hole cut into the cardboard cover. Turn ON the overhead and turn off the room lights. Place 3 drops of sulfuric acid in the Sodium Thiosulfate beaker and stir. The mixture will start to form sulfur precipitate and as the crystals grow more and more light is scattered. Initially, the beaker will begin to "glow" with a bluish light as viewed from the side. The spot on the screen (view from the top) will begin to turn red as all the blue light is scattered in the beaker.

Once the 3 drops of Sulfuric Acid is added to the Sodium Thiosulfate solution, the whole process takes about a minute and a half before the solution turns fully opaque, a cloudy white, and the red spot on the screen turns dark.


  • Beaker
  • Beaker of water
  • eye dropper