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Quantum Physics

Quantum Physics. Physics History. Physics History. Physics History. Why do the stars shine?why do the elements exhibit the order that’s so apparent in the periodic table? How do transistors and microelectronic devices work?why does copper conduct electricity but glass doesn’t?. Why?.

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Quantum Physics

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  1. Quantum Physics

  2. Physics History

  3. Physics History

  4. Physics History

  5. Why do the stars shine?why do the elements exhibit the order that’s so apparent in the periodic table? How do transistors and microelectronic devices work?why does copper conduct electricity but glass doesn’t? Why?

  6. Quantum Physics Particle Theory of Light De Broglie Hypothesis Photo-electriceffect Compoton effect Hydrogen spectrum Uncertainty Wave Function Schrodinger equation and application

  7. Quantum Blackbody Radiation Planck’s hypothesis The photoelectric effect The particle theory or light X-rays Diffraction Photons Electromagnetic Key words

  8. The wave properties of particles The uncertainty principle The scanning tunneling microscope Atomic Spectra The Bohr Theory of Hydrogen Key words

  9. Classical theory Experimental data Intensity Wavelength 27.1 Blackbody Radiation and Planck’s Hypothesis Ultraviolet Catastrophe

  10. Planck’s Hypothesis In 1900 Planck developed a formula for blackbody radiation that was in complete agreement with experiments at all wavelengths . Planck hypothesized that black body radiation was produced by submicroscopic charged oscillators, which he called resonators. The resonators were allowed to have only certain discrete energies, En, given by

  11. I Is Il higher - I Il loweer A K A V o -Va V pow 27.2 The Photoelectric Effect and The Particle Theory of Light 1.The Photoelectric Effect 1) saturated current is proportion to intensity of light  is fixed,I is proportion to voltage,but there’s a saturated current which is proportion to intensity of light

  12. I Is Il higher - I Il loweer A K A V o -Va V pow inverse voltage is applied，Ic=0. Va is called cutoff voltage or stopping voltage

  13. 2) initial kinetic energy is proportion to the frequency of incident light,has no relation with the intensity of light 3) there’s a cutoff frequency (threshold frequency) to a metal,only when >o, there’s a current 4) photo current produce immediately,delay time is not more than 10-9s。

  14. 2.Einstain’s theory 1)the hypothesis of Einstian Light has particle nature Intensity of light 2) Einstian equation A work function

  15. Notes: a. the initial kinetic energy is linearly proportion to the frequency of incident light b. Cutoff frequency While ＜A/h时，no photoelectric effect c. instantaneously effect

  16. 3.the wave-particle duality 1) Light has dual nature 2) the energy, momentum and mass energy momentum M0=0 Mass:

  17. Example :the experiment result is as follows,find h eUa  o s q p 1.oq 2.op 3. op/oq 4. qs/os solution：3

  18. Example: the cutoff o=6500Å, the light with  =4000Å incident on the metal (1)the velocity of photoelectrons? (2)stopping voltage? Solution:  =6.5×105(m/s) (2) c = h= 6.63×10-34 : Va=1.19 (V)

  19. I I (A) (B) o o V V I I (D) (C) o o V V Example:incident frequency is fixed；we’v experimental curve (solid line),and then with fixed intensity of light,increase the incident frequency，the experimental curve is as dot line,find the correct answer in the following graphs

  20.  27.3 The Compton Effect 1.scattering light go through medium and propagate in different direction。 from classic view:the scatter wavelength is same with incident wavelength。 but in graphite experiment,we found a change in wavelength,this is called compoton scatter。

  21. y  x:  x m y: 2.principle suppose: photos collide with electrons without loss of energy Energy conservation ho+moc2= h +mc2 Momentum conservation： c=

  22. y   x m Å =0， min=o ; =180°, max=o +2c Compton wavelength：

  23. The explanation to compton effect 1)photon pass some energy to electrons 2)compton effect is strong when the photon act on the atom with small number atom

  24. 3) meaning：photon theory is correct show the duality nature of light 4) micro particle obey the conservative law 5) photoelectric effect, compton effect

  25. Example: with o =0.014Å X ray in compton experiment, find maxmum kinetic energy in electrons？ solution:fron energy conservation ，Emax in fact max=o +2c ， =1.1×10-13 J

  26. Example:o =0.1Å X ray in experiment。In the direction of 90°,find wavelength? Kinetic energy and momentum of electron? solution:  =90°   = o + =0.1+0.024=0.124Å =3.8×10-15 J

  27. y  x:  x m y: From momentum conservation  =90° =8.5×10-23 (SI)

  28. (2) for example:o =0.03Å X ray in experiment, the velocity of recoil electron  =0.6c, find(1)the rate of the scattering energy of electron to its rest energy (2)the scattering =? And scattering  =? solution: (1)the scattering energy =0.25moc2   = 0.0434Å so  =63.4°

  29. 27.4 Line Spectra and Bohr Model 1.the atomic hydrogen spectrum 2.the empirical formula of Balmer Rydberg constant

  30. The line spectrum system Lyman series ultraviolet Balmer series visible Baschen infrared General form:

  31. Physicist: Rutherford

  32. 3.Bohr model  hypothesis 1)stationary hypothesis: electrons can be in some certain stable orbits 2) quantum transition: 3) quantization of angular momentum  to hydrogen atom

  33. Notes: 1.Ground state n=1 2.excited state n>1 3.n=2,the first excited state 4.ionization: 5. explanation of hydrogen spectrum

  34. n=4 lyman n=3 n=2 Balmer n=1 r =a1 r =4a1 r =9a1 r =16a1 Paschen

  35. T=R/n2 En=hcR/n2  6 hcR/25 5 4387cm-1 Brackett 4 6855cm-1 hcR/16 Paschen hcR/9=-1.51eV 3 12186cm-1 Balmer hcR/4=-3.39eV 2741cm-1 2 lyman hcR=13.6eV 109677cm-1 1 Energy level diagram

  36. Example:find the energy for hydrogen atom giving longest wavelength in lyman series? 1)1.5ev 2)3.4ev 3)10.2ev 4)13.6ev solution:3 n=2-1

  37. Example:with 913A violent light,hydrogen atom can be ionized,find the wavelength expression of lyman series solution：4

  38. Example:with visible light,can we ionized the first excited state of hydrogen atom? Solution: Needed enrgy no

  39. 4 -0.85 -1.51 3 -3.4 2 -13.6 1 Example: hydrogen atom in third excited state,find the number of its line after transition,name its series？ solution: lyman: 3 Balmer: 2 Pachen： 1

  40. Physicist: De Broglie

  41. 27.5 Wave Nature of Particles chapter 42 Quantum Mechanics 1. De Broglie wavelength Particle nature of light: Notes:1)

  42. Notes:1) example：a bullet with m=0.01kg，v=300m/s h is so small,the wavelength is so small It’s difficulty to measure,behave in particle nature On the atomic scale,however,things are quite different Me=9.1*10-31,v=106, =0.7nm This wavelength is of the same magnitude as interatomic spacing in matter,and in diffraction experiment the phenomena is evidence.

  43. Standing wave 2) quantization condition of angular momentum of Bohr is the showing of de broglie wave

  44. 2. experiment diffraction by electrons （Thomoson1927） • slit,double slit diffraction

  45. G d M  Experiment Davision and Germer experiment A  

  46. example:(1)the kinetic energy of electron Ek=100eV；(2)momentum of bullet p=6.63×106kg.m.s-1, find 。 solution:for the small kinetic energy,with classic formula =1.23Å h= 6.63×10-34 (2)bullet = 1.0×10-40m conclusion:the wave nature is only obvious in microparticle,to macroparticle,you can’t detect the effect

  47. Example:with 5×104V accelerating voltage,find the  solution:with relativity effect =1.24×108(m/s) =10×10-31 (kg) mo=9.11×10-31 (kg) =0.0535Å

  48. Example：suppose ，kinetic energy equal to its rest energy， solution：2 Example:the first bohr radius a,electron move along n track， solution：

  49. 27.6 Heisenberg’s Uncertainty Relation 1.uncertainty relation It states that measured values can’t be assigned to the position and momentum of a particle simultaneously with unlimited precision. Notes: 1) represent the intrinsic uncertainties in the measurement of the x components of and even with best measure instruments. 2) small size of planck’s constant guarantees uncertainty relation is important only in atomic scale

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