Heat & Temperature

Fog Chamber

A visitor pumps a handle up and down and watches a pressure gauge rise toward one atmosphere (15 PSI) of extra pressure in an internally illuminated, glass topped, black cylinder. The temperature of the gas is also shown and it rises steadily as the gas is pumped. By pressing a button the visitor causes a valve to open which suddenly releases the extra gas into the room. The pressure in the chamber drops rapidly. The temperature drops as the gas expands, and a cloud forms in the chamber. Soon the temperature in the chamber begins to rise and the cloud evaporates. The process can be repeated over and over. This exhibit shows the connection between gas expansion, cooling, and condensation. This process plays a role in the formation of clouds and fog. Condensation of a gas to form liquid drops is a collective behavior.