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Glow Discharge (V 8)

Keyword: plasma

Demonstration Description:

Glow Discharge

The breakdown voltage in air at STP is about 3 MV/m. Pressure in the chamber is reduced as a voltage (V = 2150V) is applied resulting in the air becoming ionized. When an electrical arc (spark) is generated between the two conducting spheres the measured voltage drops to V = 1270V.
As the pressure continues to drop the mean free path of the electrons and ions increases, and the arc becomes a plasma tube. This is referred to as glow discharge. The voltage stabilizes at V = 311V.
Voltage measurements (Vmax) via 200:1 voltage divider. f = 7 kHz.
Vrms = 0.707*Vmax
Vmax = Vrms/0.707
Viewing the electrical arc and glow discharge is best in a darkened room. It is easily projected on a screen with a camera. The line spectra of nitrogen are easily viewed in a dark room with a diffraction grating.
This is historical scientific equipment, manufactured by Max Kohl A. G., Chemnitz, Germany. This company was established March 4, 1876 [1]. The date this device was purchased is unknown. One of their catalogues can be viewed online from The Smithsonian Institute [2]. Select pages from the catalogue are attached.



Induction Coil

Electrical Arc (Spark)

Glow Discharge

Glow Discharge Close Up