Ef-3 Conduction of Electricity Through Gases
Aim
To demonstrate the phenomena associated with electrical discharge under reduced pressure.
Apparatus
- Discharge tube
- Large induction coil and D.C. Powerpak
- Rotary vacuum pump
- Retort stands and clamps
Description
The apparatus is connected as shown in the diagram, care being taken that the H.T. leads do not contact earth at any point. Complete darkness is required for the details of the discharge to be seen in the lecture room. The rotary pump is started after the H.T. of the induction coil is applied.
The pressure at which the various phenomena are observed is detailed below.
PRESSURE (mm of Hg) | OBSERVATION |
50 | start of discharge |
violet streamers | |
10 | positive column |
1 | striations and Faraday dark space |
0.5 | Crookes dark space |
0.1 | striations vanish |
negative glow, Crookes dark space | |
0.02 | cathode glow, luminescence |
At the completion of the demonstration switch off the induction coil, stop the pump and leak air slowly into the discharge tube.