Model No:FHX-01
The Frank-Hertz tube in this instrument is a tetrode filled with the vapour of the experimental substance. Fig.1 indicates the basic scheme of experiment. The electrons emitted by filament can be accelerated by the potential VGK2 between the cathode and the grid G2 . The grid G, helps in minimising space charge effects.
The grids are wire mesh and allow the electrons to passthrough. The plate A is maintained at a potential slightly negative with respect to the grid G2 . This helps in making the dips in the plate current more prominent. ln this experiment, the electron current is measured asa function of the voltage VGK2 .
As the voltage increases, the electron energy goes up and so the electron can overcome the retarding potential VGA2 to reach the plate A. This gives rise to a current in the ammeter, which initially increases. As the voltage further increases, the electron energy reaches the threshold value to excite the atom in its first allowed excited state.
All the power supplies are highly stabilised and output voltages can be read on 3 V2 digit, 7 segment LED DPM with auto polarity and decimal indication through a selector switch.
Scope of Learning:
Technical Specifications:
Valve
Grid Power supplies
VG1K : 1.3-5V continuously variable
VG2A : 1.3 - 12V continuously variable
VG2K : 0 - 95V continuously variable
Multirange Digital Ammeter
Saw tooth waveform for CRO display
