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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
 Nuclear Physics
 Geiger counter
  video  - Mouse Trap Atomic Bomb
 Daedalon Geiger Counter
 Spark Detector for Alpha Particles
 Diffusion Cloud Chamber
 Larmor Precession/NMR

Diffusion Cloud Chamber


To observe the tracks left in the chamber from a radioactive source or cosmic rays.


The instruction manual for the cloud chamber is available here.

1. Adjust the chamber liner, so it touches the bottom of the chamber and all LEDs are visible. Pour 30-40mL of isopropyl alcohol 91% or higher purity into the chamber. Use pipette to wet the wall liner. After the liner is saturated, there should still be about 2 mm of alcohol on the bottom of the chamber. It will start working faster, if you do this 15 min. before next step.

2. Place the circulation pump on the bottom of a bucket and affix the drain hose to the bucket wall. Add just enough water to cover the pump inlet. Shake the pump up and down in the water to expel air from the impeller. Fill the bucket with ice (1kg per hour of operation). Connect the pump to AC power. If water does not start flowing, you may need to re-prime the pump by sucking on the drain hose.

3. Place the source rod with stopper into the hole in the viewing window. Adjust the rod up or down so that the position of the needle's eye is about 1.5 to 2 cm above the surface of the alcohol.

4. Connect the power supply to the cloud chamber.

After 5 to 10 minutes, particle tracks should become visible. Sources for both alpha and beta particles are available. If used without source cosmic ray tracks can be observed. Camera mounted above the chamber is used to display it on the screen.

Includes built-in high voltage (~800V) power supply for clearing the chamber of unwanted ions (this is the yellow wire that attaches to the top of the needle).


!! It is very important to unplug the chamber power supply when finished!!

To prevent water from freezing and damaging the heat exchanger, leave circulation pump on.
Use 210Po source. It gives better tracks.


  • Cloud chamber
  • Radioactive Source
  • Ice Water Bath