Franck-Hertz Apparatus
by United Scientific

In this experiment, electrons contained in a vacuum tube with a small amount of vapor are accelerated towards an anode grid. Beyond that is a second electrode with a negative potential with respect to the anode, so that only the electrons with a certain minimum of energy can reach the second electrode. The current reaching this second electrode is then monitored as the accelerating voltage is increased.

The argon vapor tube has been enclosed in the metal casing of the unit, protecting it from damage as well as shielding it from stray environmental charges.

The Franck-Hertz Apparatus can be used alone for the manual recording of the voltage-current curves, or in conjunction with an oscilloscope (not included) in XY mode for the repeated sweeping of the accelerating voltage. The built-in panel meters of the instrument are capable of measuring and indicating the current and the three tube voltages, while the current amplifier has four ranges from 10^-5A to 10^-8A for full scale deflection. A simple switch allows the voltages on the control grid, the anode and the reverse bias electrode to be monitored in turn.

While the original Franck-Hertz device used mercury vapor that was heated to approximately 180°C, this model uses argon vapor at room temperature because argon is much easier to control, and does not pose the health hazards associated with mercury. In addition to this, up to five minima can be obtained with manual plotting.

Included with the apparatus is a complete operator’s manual.

Specifications:

Tube Voltages
-Control Grid: 1.3-5.0V
-Acceleration: 0-100V
-Reverse Bias: 1.3-15V

Oscilloscope scan: 0-50V, 115+/-20Hz

Recommended accessories:
-Oscilloscope w/XY Function
-Banana Plug connecting cords