this is from the exel textbook... i don't have the diagrams in there sorryh Perform an investigation and gather first hand information to observe the occurrence of different striation patterns for different pressures in discharge tubes
Aim: To investigate the effect of different gas pressures on an electric discharge passing through a series of discharge tubes.
Apparatus: power supply, induction coil, discharge tubes or varying pressure, connecting wires
Theory: when a high voltage from an induction coil is applied across the terminals of a discharge tube, a discharge may result. Electrons from the cathode travel towards the positive terminal exciting electrons in the atoms of the gas as the collide. The gas density affects the type of collision between the gas atoms (often hydrogen) resulting in different effects.
Method: the apparatus was set up as in the diagram:
The induction coil was adjusted so that a continuous spark was produced. The negative terminal of the induction coil was connected to the top plug of the first discharge tube (cathode) and the positive terminal was connected to the bottom plug (anode). Observations made of the effect of different pressures on the discharge tube by moving the top plug along to different tubes
Results:
1. Coloured streamers appear and both the anode and the cathode are surrounded by luminous glow
2. At a pressure of 0.1-0.2 kPa the positive glow extends along the tube, taking up about half its length. Between the positive glow and the negative glow is an area called the Faraday dark space
3. As the pressure is reduced further the positive column breaks up into series of striations
4. At a pressure of 0.01 kPa Crookes dark space fills the entire tube and a green glow appears in the glass at the end of the discharge tube opposite the cathode
5. Diagram:
Conclusion: As the pressure of the gas was reduced in the discharge tube, there were changes in discharge. As the lowest pressure, no gas glow was observed but a glow form the cathode rays was noted in the glass opposite the cathode.
