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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