What is James Franck known for in physics?
My most significant contribution, alongside Gustav Hertz, was the Franck-Hertz experiment. Let us first observe what nature tells us. We bombarded mercury vapor with electrons of carefully controlled energies. What we saw was that electrons could only transfer specific amounts of energy to the mercury atoms. This occurred only when the electron's energy matched a particular discrete value. The evidence suggests this demonstrated that atoms do not absorb or emit energy continuously, but in distinct packets, or quanta. This provided crucial experimental support for the nascent quantum theory, showing that atomic energy levels are quantized. It was a direct observation of the quantized nature of matter.
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