Ionising bulb fill gases


Crookes radiometer
A crookes radiometer is filled with air at a pressure of about 1 Torr. This ionises easily in the RF field and gives a characteristic pale cyan glow due to the nitrogen and oxygen mixture. The vanes of the radiometer turn slowly when the glow is initiated, but the rate diminishes and they come to a standstill after about a minute. This is because the molecular bombardment that makes them turn in sunlight is an adiabatic process, whereas RF heating eventualy brings the system into thermal equilibrium.



Discharge Tubes

© D. W. Knight, 2013