Franck–Hertz experiment

The Franck-Hertz experiment, conducted by James Franck and Gustav Hertz in 1914, is a foundational experiment in quantum physics that demonstrated the quantized nature of energy levels in atoms. It provided strong evidence for the existence of discrete energy states in atoms, which was a pivotal development in the understanding of atomic structure and quantum mechanics. ### Experimental Setup: In the experiment, a tube containing low-pressure mercury vapor was used.