Geissler Tube
Use
It emits light when it is applied a potential difference which is very high.
Description
It is a glass tube with two electrodes soldered on its ends and within which there is gas under very low pressure.
Functioning
If we put a gas, at atmospheric pressure, into the tube and we apply a very high potential difference (several thousands of volts), we can see that it acts as electrical insulation and, consequently, no current flows through it. Nevertheless, if we decrease its pressure gradually (connecting the tube to a vacuum plump), it eventually becomes a conductor and emits a luminous radiation whose colour depends on the gas used.
History
They were invented by German physicist Heinrich Geissler in 1857, as a consequence of the trials conducted with the mercury vacuum plump that he had developed.
