Adiabatic Expansion Of Air - Fog In Bottle

Purpose

To demonstrate adiabatic cooling of air.
 

Equipment

Bottle with water, cork and plastic tube with bicycle tire pump, small tensor lamp.

 

Images

i5-12

Description

A bottle containing a small amount of water is sealed by a stopper. A tube passes through the stopper and is attached to a bicycle tire pump which is pumped to pressurize the bottle. When the pressure rises to a sufficient level it blows the stopper off the bottle, allowing the air to expand adiabatically and cool. The cooling process condenses water vapor in the bottle, producing fog. If the stopper is quickly replaced and the pressure in the bottle increased, the air becomes warmer and the fog disappears. A small lamp illuminates the bottle to make the fog very visible, even in a large room
 

References

J. J. Coop, A Demonstration of Fog Production, AJP 9, 242 (1941).