Franck-Hertz Apparatus II

Quick Answer: Franck-Hertz Apparatus II is an updated benchtop instrument that demonstrates the quantization of atomic energy levels through a repeating current-voltage curve.

Inside a vacuum tube filled with a trace of argon gas, an electron beam is accelerated toward a counterelectrode guarded by a voltage barrier that only lets through electrons arriving with enough energy. At low accelerating energy, electrons collide elastically with argon atoms and lose almost no energy, clearing the barrier; as the accelerating voltage rises, collisions eventually transfer one whole quantum of energy to an argon atom, leaving the electron too weak to pass — so the current drops. Because this recurs at regular voltage intervals, the current-versus-voltage trace shows repeating maxima and minima, direct evidence that argon atoms absorb energy only in discrete amounts. This improved model adds updated electronics with better stabilization, digital voltage and current readouts, and fully shielded coax cables that keep the current curve clean — producing 5-7 current maxima per scan, with anode current measured over 0.1nA-1µA and voltage/current shown on 3-1/2 digit readouts, run as an automatic scan to an oscilloscope or chart recorder, or stepped through manually. First performed by James Franck and Gustav Hertz in 1914, the experiment earned the pair the Nobel Prize in Physics in 1925 and remains a landmark physics lab equipment India demonstration of quantum theory.

It is part of EduScope India's Physics Lab Equipment range, and is best studied alongside the Hall Effect Apparatus and a Multimeter, Digital for advanced electrical and electronic physics coursework.