Download Yiming Abulaiti

Franck-Hertz
experiment
Yiming Abulaiti
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Outline
Bohr model of hydrogen atom
Energy level of a Mercury atom
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Principle the Franck-Hertz experiment
Sketch of the experimental apparatus Summary
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Bohr model of hydrogen atom (1913)
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- Atoms can exist only in certain bound energy states.
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- Explained discrete spectrum of hydrogen atom.
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E2 -E1 = hv
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Where h is planck’s constant, and v
is the frequency of the photon.
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Energy level of a Mercury atom
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- quantized energy levels.
- two electrons in n = 6, l = 0
spectroscopic notation:
Ground state: 1S0
2S+1L
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excited state: 3P0 , 3P1 , 3P2, 1P1
Energy difference : Eexcited - Eground
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Principle the Franck-Hertz experiment (1914)
- Electron can transfer energy to mercury atom
Accelerate electron: Efree = e Va Where Va is acceleration voltage.
inelastic collision: free
electron loose energy
and bound electron
absorb energy.
- Can a Mercury atom absorb any amount of energy?
Mercury atom exited when :
KE >= E2-E1
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Sketch of Franck-Hertz Apparatus
* Electron flux produce current in the
circuit and it can be measured.
- Measurement
* When electrons loose their
energy during the collision with
mercury atoms, the current drop
down.
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Summary
- Quantised energy level of atoms
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- Frank-Hertz experiment explored the
existence of excited energy levels of
mercury atom.
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Additional material
- Online simulation of this experiment
http://phys.educ.ksu.edu/vqm/free/FranckHertz.html
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