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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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 Quantum Effects
 Atomic Physics
  video  - Emission Spectra
 Street Lamps Collection
 Nuclear Physics

 video  - Emission Spectra


To observe the different spectra of ionized gases such as H2, He, Ne, Hg using a diffraction grating. Light with longer wavelength (red) diffracts at a larger angle, light with shorter wavelength (blue) diffracts at a smaller angle.


REFERENCE: Spectrum Tube Description from ETP Inc.

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Pass out gratings to students (or use video camera with grating taped to front lens) and have them observe the different line spectra of the gases while turning on the tubes for only 30 seconds at a time. The tubes are easily changed and the spectra are quite beautiful. The gratings can also be rotated to show some recombination of the separated colors.

The gases available are:
  • Hydrogen
  • Deuterium
  • Helium
  • Nitrogen
  • Oxygen
  • Air
  • Neon
  • Mercury
  • Incandescent Lamp


INCANDESCENT - a vertical light bulb can be used to show the students all the colors in white light

PRISM - uses refraction to spread light, red disperses less than blue - this is opposite what you see with a diffraction grating

DIFFRACTION - grating uses diffraction to spread light, light with longer wavelength (red) diffracts at a larger angle, light with shorter wavelength (blue) diffracts at a smaller angle

Turn the lamps on for only 30 seconds at a time. Turn off for 30 seconds to allow tube to cool before turning on again. This is to avoid the tubes from getting too hot and accelerating its degradation.


  • Spectrum Tube Power Supply
  • Diffraction Gratings
  • Spectrum Tubes