Franck-Hertz experiment with neon – Recording with the oscilloscope or point-by-point

In experiment P6.2.4.3, electrons are accelerated in a glass tube filled with neon gas. The glass tube contains four electrodes: the cathode K, the grid-shaped control electrode G1, the accelerating grid G2 and the collector electrode A. As in the Franck-Hertz experiment with mercury, the accelerating voltage is increased continuously and the current of those electrons that can overcome the retarding voltage between G2 and A and reach the collector is measured. The collector current becomes minimal whenever the kinetic energy immediately in front of grid G2 is just sufficient for the collisional excitation of neon atoms, and it rises again at higher accelerating voltages. Clearly separated reddish luminous layers are observed between grids G1 and G2; their number increases with rising voltage. These are zones of high excitation density in which the excited atoms emit spectral light. The Franck-Hertz curve is recorded either manually or with an oscilloscope.