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 tubes described below. There are two tubes available, 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. 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 Mercury and Oven
Free electrons colliding with mercury atoms emit energy in quantized packet. The excitation energy at 4.9 eV can be determined. A highly-evacuated cathode ray tube with mercury gas filling and plane-parallel electrodes in order to avoid distortion of the field lines. Electrodes include an indirectly heated, oxide cathode, perforated to produce a homogenous electric field plus an anode grid and collector (counter) electrode. In order to raise the probability of collisions between electrons and mercury atoms to a sufficient amount, the tube needs to be heated using a special heater. This heater is used for adjusting the vapor pressure in the mercury filed tube. It is a spray painted metal housing with the tube symbols printed on the front panel that are visible from a distance, ceramically insulated connection sockets, viewing windows, opening with spring clamp for thermometer in the lid, insulated carrying handle and built-in thermostat for adjusting temperature. The TEL 8482135 Power supply unit for Franck-Hertz experiment is also required.
|Heater||4-12 V AC/DC|
|Grid voltage||0-70 V|
|Operating temperature||200 degrees C|
|Heater||115V AC 400W|
|Temperature range||160-240 degrees C|
|Constant temperature precision||±5 degrees C|
|Replacement Mercury filled Franck-Hertz Tube|
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 TEL 8482135 Power supply unit for Franck-Hertz experiment is also required.
|Replacement Neon filled Franck-Hertz Tube|
Power Supply unit for Franck-Hertz Experiment
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|
|Signal output||0 –12 V @ 7 nA/V|
|Accelerating voltage||UA/10 for oscilloscope|
|Connections||via 4 mm safety sockets|
Franck-Hertz Experiment with Mercury|
This system includes the Franck-Hertz tube with mercury filling and Heater, TEL-8482150 as well as the Power Supply Unit. TEL 8482135. A dual beam analog oscilloscope with X-Y feature is also required. (The oscilloscope shown is not part of the system but can be purchased separately).
Franck-Hertz Experiment with Neon|
This system includes the Franck Hertz tube with neon, the Power Supply Unit for Franck-Hertz Experiment. A dual beam analog oscilloscope with X-Y feature is also required. (The oscilloscope shown is not part of the system but can be purchased separately).