Franck-Hertz Experiment

Claimed and created by Tyler Bennett

Main Idea

Accelerating Apparatus

Data from the apparatus

James Franck and Gustav Hertz were German physicists that helped to prove the Quantum Theory using their collisional excitation experiment in 1914. The quantum theory states that atoms have discrete levels made up of electrons of specific kinetic energies for each level. To confirm this, the Franck-Hertz duo created an accelerating apparatus, which simply sends electrons with varying kinetic energies through a vapor (in this case, mercury vapor) and then collects the electrons that weren’t picked up by the atoms in the vapor. The results showed that once the electrons reached the threshold kinetic energy of 4.9 eV, most of them were picked up by the atoms, and they didn’t reach the collector. This proved that the first level of the mercury atoms needs electrons with at least 4.9 eV to be absorbed. This technique was used with other elements to find their own threshold kinetic energies.

A Mathematical Model

where [math]\displaystyle{ E_{H*, f} }[/math] is the final energy of the atom plus the energy of the electrons and [math]\displaystyle{ K_{e, f} }[/math] is the final energy left over by the passing electrons. [math]\displaystyle{ E_{H, i} }[/math] and [math]\displaystyle{ K_{e,i} }[/math] are the initial quantities of the atom and the electron before the collision of the two or before the absorption of the photon. This equation is consistent with conservation of energy, meaning that there is no loss or gain of energy from outside of the system.

1. For example [math]\displaystyle{ {\frac{d\vec{p}}{dt}}_{system} = \vec{F}_{net} }[/math] where p is the momentum of the system and F is the net force from the surroundings.

A Computational Model

How do we visualize or predict using this topic. Consider embedding some vpython code here Teach hands-on with GlowScript

Examples

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Connectedness

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History

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In 1911, Ernest Rutherford created a model of the atom which was proven wrong in the next couple of years. His model displayed only a single level that spiraled about the nucleus of the atom. Niels Bohr noted that this model would mean that atoms could not exist, as the electrons would spiral into the nucleus. Bohr then came up with his own model in 1913 that consisted of different shells outside of the atom. The electrons could jump shells and they would have constant quantized orbits. The Franck-Hertz experiment confirmed this model in showing that atoms can only obtain electrons when they contain enough kinetic energy to be able to jump onto the atoms’ shells.

See also

Quantum Theory Ernest Rutherford Niels Bohr

Further reading

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External links

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References

[1] [2] [3] [4]