Franck-Hertz Neon System

Franck-Hertz Neon System



This system includes the Franck Hertz tube with neon and the Power Supply Unit for Franck-Hertz Experiment. The quantized absorption of energy by atoms was some of the first evidence supporting the Bohr model of the atom. Electrons can transfer only quantized amounts of energy to the Neon atoms, resulting in a current that varies periodically as the accelerating voltage increases.

Add To Cart


In 1913 Franck and Hertz first performed the important experiment demonstrating discrete energy states in atoms. This experiment demonstrating the quantization of energy as well as the recording and evaluation of spectra is included in most of the curricula used around the world. 

This experiment can be performed with the Franck-Hertz tube described below. There are two different tubes available, a Neon filled tube and a Mercury filled tube (which requires a heater). Both tubes require the specially designed power supply shown as well as an oscilloscope (not included). We have packaged the required items in convenient systems, however, replacement tubes are available separately. Additionally if you want to purchase both the Ne and Hg tube only one of the special power supplies is required. 

Franck- Hertz Tube with Neon

Free electrons colliding with Neon atoms emit energy in quantized packet. The excitation energy at about 19 eV can be determined. When excited, these states emit visible light due to the energy drop from intermediate levels to a ground state at excitation energy of about 16.7 eV. The light so emitted is in the red-yellow region of the spectrum. Bands of light develop between the control grid and the accelerating grid. The plane-parallel geometry of the grids means that these bands can be vied through a window. Unlike the mercury-filled the Franck-Hertz tube, the neon filled tube can be operated at room temperature. Electrodes include an indirectly heated cathode, mesh control grid, mesh accelerating grid and collector (counter) electrode. The tube is mounted on a base with color-coded connections sockets. The Franck-Hertz power supply is included with this system.


Filament voltage 4-8 V AC/DC

Control potential 9 V

Accelerating voltage max 80 V

Countervoltage 1.2 – 10 V DC

Tube 130X26 Ø mm

Base w/sockets 190X115X115 mm

Weight 450 g

Franck-Hertz power supply
This power supply unit is designed for operating either the Ne or Hg filled Franck-Hertz tube. It provides all the voltages needed to power the tubes and includes a sensitive built-in DC amplifier for measuring collector current. The accelerating voltage can be provided manually or be means of a saw-toot output voltage from the power supply unit. Additional measuring inputs are also available for the anode current and accelerating voltage.


Filament voltage 4-12 continuously adjustable

Control voltage 9 v @ 10 mA

Accelerating voltage 0 –80 V

Operating modes manual, continually adjustable Saw-tooth (60 Hz)

Countervoltage 1.2 – 10 V continually adjustable

Analog outputs:

Signal output 0 –12 V @ 7 nA/V

Accelerating voltage UA/10 for oscilloscope

Connections via 4 mm safety sockets

Dimensions 160X132X210 mm

Weight 2.4 kg

(The oscilloscope and connecting cables shown are not included as part of the system).