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. There are four electrodes in the glass tube: the cathode K, the grid-type control electrode G1, the acceleration grid G2 and the target electrode A. Like the Franck-Hertz experiment with mercury, the acceleration voltage is continuously increased and the current of the electrons which are able to overcome the opposing voltage between G2 and A and reach the target is measured. The target current is always lowest when the kinetic energy directly in front of grid G2 is just sufficient for collision excitation of the neon atoms, and increases again with the acceleration voltage. We can observe clearly separated luminous red layers between grids G1 and G2; their number increases with the voltage. These are zones of high excitation density, in which the excited atoms emit light in the visible spectrum. The Franck–Hertz curve is recorded either manually or using an oscilloscope.