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Franck–Hertz experiment
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Collisions confirm quantised energy levels.
Electrons accelerated through mercury vapour lose energy in steps of 4.9 eV, causing current drops at 4.9 V intervals and UV emission at 254 nm, showing quantised atomic levels.
1914 experiment.
Direct proof of discrete levels.
In more detail
The Franck-Hertz experiment passed electrons through mercury vapour and observed sharp drops in current at specific voltages. These drops showed that atoms absorb energy in discrete amounts.
Real-world uses
- It provided direct evidence for quantised atomic energy levels.
- It is a classic demonstration in atomic physics labs.
- The Franck–Hertz experiment is a classic lab demonstration of quantised energy transfer between electrons and gas atoms.
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Frequently asked questions
What do the dips show?
Electrons lose energy in discrete steps when they excite mercury atoms.
Who performed it?
James Franck and Gustav Hertz, in 1914.
What did the experiment show?
Electrons lose energy in discrete steps when colliding with atoms, which confirms quantised energy levels.
Related topics in Atomic & Nuclear Physics
Rydberg constant · Absorption and emission spectra · Ionisation energy · Characteristic X-rays · Continuous X-ray spectrum · Moseley's law