CLOUD CHAMBER:  DEMONSTRATE FOG FORMATION BY EXPANSION, NEED FOR NUCLEI.

 

Schematic of the cloud chamber setup.

 

INSTRUCTIONS:

  1. CHECK OIL LEVEL IN PUMP BEFORE STARTING (Oil should show in the window at the end of the blue pump housing)
  2. Setup as shown above.  Use a 1/4" vertical slit slide in the projector.  The slit should cover about 1/3 the width of the tank and all of the height.   Turn on the slit lamp.
  3. With valves closed, turn on pump and evacuate holding tank
  4. Leave pump running (DO NOT TURN PUMP OFF WITH VACUUM IN HOLDING TANK - RELEASE VACUUM BY OPENING BOTH VALVES BEFORE TURNING PUMP OFF).
  5. With inlet valve closed, open exhaust valve to drop pressure the modest amount.  Usually, if the tank has not been nucleated recently, no cloud will form.
  6. Close the exhaust valve and open the inlet valve.  Light a match and by opening the exhaust valve slightly, let a little LITTLE smoke in through the inlet.  Close both valves.
  7. Now with some nuclei inside, opening the exhaust valve and lowering the pressure a modest amount will produce a fog.  More pressure drop = more dramatic fog.

 

QT Movie of a cloud forming.


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2000.  John Hart, University of Colorado