The Franck-Hertz tube consists of an electron-emitting cathode, two mesh grids for accelerating electrons, and an anode plate for collecting them. It is filled with low-pressure gas. The mesh grids accelerate electrons, while the anode, held at a slightly negative potential, provides braking.At low accelerating potential, electrons undergo elastic collisions with gas atoms.
As the potential increases, inelastic collisions excite gas atoms, causing them to absorb energy. This reduces the number of electrons reaching the anode, creating dips in the plate current. These dips occur at fixed intervals, demonstrating quantized energy levels in Bohr’s atomic model.In the neon gas Franck-Hertz experiment, absorbed energy is released as red-orange photons, forming visible bands