Electric discharge

[1] The properties and effects of electric discharges are useful over a wide range of magnitudes.

A low steady current can illustrate the gas spectrum in a gas-filled tube.

A flashtube generates a short pulse of intense light useful for photography by sending a heavy current through a gas arc discharge.

A spark gap is used in internal combustion engines to ignite the fuel/air mixture on every power stroke.

Spark gaps are also used to switch heavy currents in a Marx generator and to protect electrical apparatus.

Voltage versus current characteristics for neon gas at 1 Torr pressure between flat electrodes spaced 50 cm.
A-D dark discharge
A-B: non-self-sustaining discharge and collection of spontaneously generated ions.
B-D: the Townsend region , where the cascade multiplication of carriers takes place.
D-I glow discharge
D-E: transition to a glow discharge, breakdown of the gas.
E-G: transition to a normal glow; in the regions around G, voltage is nearly constant for varying current.
G-I: represents abnormal glow, as current density rises
I-K arc discharge .