Quantum+physics+and+Nuclear+physics

Electrons ejected from a sodium metal surface were measured as an [|electric current]. Finding the opposing [|voltage] it took to stop all the electrons gave a measure of the maximum [|kinetic energy] of the electrons in [|electron volts]. The minimum energy required to eject an electron from the surface is called the photoelectric work function. The threshold for this element corresponds to a wavelength of 683 nm. Using this wavelength in the [|Planck relationship] gives a photon energy of 1.82 eV. =Davisson-Germer Experiment=
 * Early Photoelectric Effect Data **
 * [[image:http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/imgqua/davgermer.gif align="center"]]

Davisson, C. J., "Are Electrons Waves?," Franklin Institute Journal 205, 597 (1928) || The [|Davisson-Germer experiment] demonstrated the wave nature of the electron, confirming the earlier hypothesis of deBroglie. Putting wave-particle duality on a firm experimental footing, it represented a major step forward in the development of quantum mechanics. The [|Bragg law] for diffraction had been applied to x-ray diffraction, but this was the first application to particle waves. Davisson and Germer designed and built a vacuum apparatus for the purpose of measuring the energies of electrons scattered from a metal surface. Electrons from a heated filament were accelerated by a voltage and allowed to strike the surface of nickel metal. || The electron beam was directed at the nickel target, which could be rotated to observe angular dependence of the scattered electrons. Their electron detector (called a Faraday box) was mounted on an arc so that it could be rotated to observe electrons at different angles. It was a great surprise to them to find that at certain angles there was a peak in the intensity of the scattered electron beam. This peak indicated wave behavior for the electrons, and could be interpreted by the Bragg law to give values for the lattice spacing in the nickel crystal. The experimental data above, reproduced above Davisson's article, shows repeated peaks of scattered electron intensity with increasing accelerating voltage. This data was collected at a fixed scattering angle. Using the Bragg law, the [|deBroglie wavelength] expression, and the kinetic energy of the accelerated electrons gives the relationship In the historical data, an accelerating voltage of 54 volts gave a definite peak at a scattering angle of 50°. The angle theta in the Bragg law corresponding to that scattering angle is 65°, and for that angle the calculated lattice spacing is 0.092 nm. For that lattice spacing and scattering angle, the relationship for wavelength as a function of voltage is empirically Trying this relationship for n=1,2,3 gives values for the square root of voltage 7.36, 14.7 and 22, which appear to agree with the first, third and fifth peaks above. Then what gives the second, fourth and sixth peaks? Perhaps they originate from a different set of planes in the crystal. Those peaks satisfy a sequence 2,3,4, suggesting that the first peak of that series would have been at 5.85. That corresponds to an electron wavelength of 0.21 nm and a lattice spacing of 0.116 nm ?? I don't know if that makes sense. I need to look at the original article. =Hydrogen Spectrum=

This spectrum was produced by exciting a glass tube of hydrogen gas with about 5000 volts from a transformer. It was viewed through a [|diffraction grating] with 600 lines/mm. The colors cannot be expected to be accurate because of differences in display devices. For atomic number Z = , a transition from n2 = to n1 = will have wavelength λ = nm and [|quantum energy] hν = eV At left is a hydrogen spectral tube excited by a 5000 volt transformer. The three prominent hydrogen lines are shown at the right of the image through a 600 lines/mm diffraction grating. An approximate classification of [|spectral colors]: Radiation of all the types in the [|electromagnetic spectrum] can come from the atoms of different elements. A rough classification of some of the types of radiation by wavelength is:
 * [[image:http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/modpic/hydtube.jpg]] ||
 * Violet (380-435nm)
 * Blue(435-500 nm)
 * Cyan (500-520 nm)
 * Green (520-565 nm)
 * Yellow (565- 590 nm)
 * Orange (590-625 nm)
 * Red (625-740 nm) ||
 * Infrared > 750 nm
 * Visible 400 - 750 nm
 * Ultraviolet 10-400 nm
 * Xrays < 10 nm

=Quantized Energy States= The electrons in free atoms can will be found in only certain discrete energy states. These sharp energy states are associated with the orbits or shells of electrons in an atom, e.g., a hydrogen atom. One of the implications of these quantized energy states is that only certain [|photon energies] are allowed when electrons jump down from higher levels to lower levels, producing the [|hydrogen spectrum]. The [|Bohr model] successfully predicted the energies for the hydrogen atom, but had [|significant failures] that were corrected by solving the [|Schrodinger equation] for the hydrogen atom.