TEL-2533.02DAS3

A variation of the Franck-Hertz experiment can be performed with the Hertz Critical Potentials Tube. With this tube a beam of electrons is emitted from a hot filament and is accelerated through He or Ne gas at low pressure. (The inside surface of the glass bulb is coated with a transparent conducting layer connected to the anode to create a field-free region.) When this beam reaches a certain critical energy, inelastic collisions occur between He or Ne electrons and the electron beam. The electrons in the beam then lose their energy and are collected by a collector ring in the tube which is kept slightly positive with respect to the anode. As the electron beam continues to be accelerated, a higher critical energy is reached. At this higher energy inelastic collisions again occur between the He or Ne electron and the electron beam. Another peak will occur in the collector current. This second peak represents an energy level that is distinct and different from the first collision.

By monitoring the accelerating voltage vs. ring current 5 - 7 different and distinct energy levels plus the energy required for ionizations can be observed. (In contrast, the Franck-Hertz experiment allows you to determine only one energy level.)

The Hertz Data Acquisition System in He includes a He filled Hertz tube, TEL-2533.02; a Universal Stand, TEL-2501; a He filled Spectrum tube whose spectrum can be viewed with a Diffraction Grating Spectroscope (not included). In addition the Franck Hertz power supply TEL-8482530-115 is also provided. This convenient to use apparatus incorporates both a 0-60VDC ramped accelerating voltage output and a picoammeter to measure the ring current (which corresponds to the excitation levels). Both the accelerating voltage and ring current are available as signal outputs with a 1 volt FS deflection for easy and straight forward connection to a computer interface, digital storage oscilloscope, or chart recorder.  (Cables and oscilloscope not included.)