8.04 Lecture 2, Experimental Facts of Life

Notes

Facts of life:

1. Atoms exist
   • but the electrons are not orbiting around, because when an electron orbits it radiates, losing energy, would die quickly
2. Randomness exist
   • Geiger counter
3. Atomic spectrum: discrete & structural
   • h2 gas excited emits light, sent throguh a prism, see discrete bands around 1000 (Lyman), 3000 (Balmer) and 10,000 (Paschen) angstroms
   • Rydberg and Ritz then found that ${\lambda }^{-1}=R\cdot (n_1^{-2}-n_2^{-2})$ for $n_i\in Z,n_2>n_1$
4. Photoelectric effect = light comes in chunks!
   • photoelectric effect = electron emitted from a material due to shining light
   • light comes in chunks with defined energy
     • $E=hv$
       • $h$ = Planck’s constant
   • intensity = # of packets
   • $kE=hV-W$
   • if your light is very low energy aka very low frequency, no intensity will be enough
   • momentum: $P=h/\lambda$
5. Electron diffraction (and interference)
   • double slit experiment = photons act as waves
     • where did wave hit screen? not localized object, some amplitude shows up everywhere = distributed everywhere = can interact at different spots
       • waves: not localized, yes interference
     • chunks: are localized, not interference (ex. a baseball)
   • what about electrons?
     • expect it to be localized, and thus no interference
   • hitachi technology demonstration
     • electron is still hitting at one spot (localized), but there is interference!
   • an electron is… an electron! both the wave and particle analogies are incomplete
   • buckyballs interfere with each other too… the limitation is technology
6. Bell’s poor inequality
   • $N(A,\overline{B})+N(B,\overline{C})\ge N(A,\overline{C})$
     • by logic!
   • $N(H,\overline{B})+N(B,\overline{W})<N(H,\overline{W})$
     • hardness = angular momentum on X axis
     • color = angular momentum on Y axis
     • whimsical = angular moment on Z axis
   • classical adding of probabilities is violated by electrons!

References

Lecture Notes: https://ocw.mit.edu/courses/8-04-quantum-physics-i-spring-2013/resources/mit8_04s13_lec02/

Lecture Recording: https://ocw.mit.edu/courses/8-04-quantum-physics-i-spring-2013/resources/lecture-2/

SP2013 MIT OpenCourseWare 8.04 Quantum Physics I