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Franck-Hertz Experiment

Stein Ingebretsen

Bohr Model

  Niels Bohr – Proposed Bohr Model   This model said that electrons occupied discrete energy levels

  Other models currently in use included   Plumb-Pudding

  Rutherford   Geiger–Marsden experiment

  Cubic

  Valiancy

  Lewis

Bohr

  Doesn’t include all quantum mechanical effects.

  Actual Bohr model holds mathematically for hydrogen, not larger atoms

Mercury Spectrum

  Shows bright bands, not a continuous emission of all wavelengths

Mercury Spectrum

  4.9 eV corresponds to a wavelength of light 253 nm

  If there are discrete energy levels, then when an accelerated electron hits mercury, it should be inelastic at 4.9 eV

Franck-Hertz

  http://phys.educ.ksu.edu/vqm/free/FranckHertz.html

Franck-Hertz

Franck-Hertz

Peak Location Data at 168 Fº

Peak  Number  A   sigA   B   sigB   Peak   Sig  Peak  

1   -­‐1.2027E-­‐10   5.3979E-­‐12   2.1594E-­‐09   1.0808E-­‐10   8.9773   0.4029  

2   -­‐2.8447E-­‐10   8.3313E-­‐12   7.8243E-­‐09   2.4181E-­‐10   13.7524   0.4028  

3   -­‐6.2581E-­‐10   2.1100E-­‐11   2.3491E-­‐08   7.8794E-­‐10   18.7685   0.6328  

4   -­‐1.3076E-­‐09   1.6138E-­‐11   6.2373E-­‐08   7.8554E-­‐10   23.8502   0.2944  

5   -­‐2.4559E-­‐09   5.0388E-­‐11   1.4209E-­‐07   2.9061E-­‐09   28.9283   0.5935  

Using a parabolic fit: y=Ax^2+Bx+C

Franck-Hertz

Franck-Hertz

Franck-Hertz

  No temperature dependence (as long as mercury is fully vaporized)

  4.961 +- .009 eV vs 4.9ev

  Supports the results of spectroscopy on mercury, and the model of the mercury atom with discrete energy levels for the electrons orbiting

Frank-Hertz

  Beautifully simple conceptually

  Easily reproducible

  Accurate and consistent results   4.961 ± .009 eV vs 4.9 eV

References

  http://en.wikipedia.org/wiki/Bohr_model

  http://nobelprize.org/nobel_prizes/physics/laureates/1922/#

  http://nobelprize.org/nobel_prizes/physics/laureates/1925/

  http://en.wikipedia.org/wiki/Cubic_atoms

  http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

  http://www.google.com/imgres?imgurl=http://image.wistatutor.com/content/feed/tvcs/Chapter2014-20.png&imgrefurl=http://www.tutorvista.com/biology/wavelength-formula&usg=__IbVTBpnXIkjehg0BwfwJdUSwz8A=&h=565&w=544&sz=4&hl=en&start=0&sig2=S2Edk3DTu2HrCBjkgT1SYg&zoom=1&tbnid=E1SkEZgyMQwfeM:&tbnh=128&tbnw=123&ei=9KqkTbOtGNO_gQf3kpjMCA&prev=/search%3Fq%3Dmercury%2Benergy%2Blevels%26hl%3Den%26client%3Dsafari%26rls%3Den%26biw%3D1250%26bih%3D862%26tbm%3Disch&itbs=1&iact=hc&vpx=120&vpy=233&dur=382&hovh=229&hovw=220&tx=119&ty=90&oei=9KqkTbOtGNO_gQf3kpjMCA&page=1&ndsp=34&ved=1t:429,r:7,s:0

  http://en.wikipedia.org/wiki/File:Mercury_Vapour_Lamp_Spectrum.jpg