Franck-Hertz Apparatus II

Classic experiment that yields basic evidence for the existence of quantum states.

The Franck-Hertz Apparatus II is an improved model of the well-known Franck-Hertz Apparatus (FHA001), featuring updated electronics with better stabilization and digital readouts for voltage and current (more robust, easier to read correctly). New fully shielded coax cables reduce electrical noise.

The Franck-Hertz Experiment yields basic evidence for the existence of quantum states. Inside a vacuum tube filled with a trace of argon gas, a beam of electrons is generated and accelerated towards a counterelectrode. A voltage barrier ahead of the counter electrode only allows electrons with a certain minimum energy to get through and make a detectable current. As the accelerating energy is increased, changes in the current are observed. On the way to the counter electrode, the electrons collide with argon atoms.

At first, nothing happens, but as the electron energy rises, it reaches enough to give one quantum of energy to the argon to ionize it. Now the electron can’t pass the voltage barrier and the cur-rent drops. The multiple valleys in the current curve are evidence of the donations of a quantum of energy.