Lab #3 writeups.
Tutorial #1 back.

The foundations of Atomic Physics: 
Today : We "clean up the mass". We will use these properties later on.
 

Side left: Interference  & Diffraction.
Side right: Atomic structure.
  From our demonstrations & labs: Light behaves like waves. 

  Or is that exactly so?

  Presentation: Double slit ("wave breakers") experiment with very very little light:

  Results: Amazing! With few photons - screen randomly illuminated. More photons: get "interference

  pattern" (There so called "garbage piles" wherever there are strong waves in the previous class).

  What's going on? 

  If the light behaves like particles - we should expect only two piles in front of the
  openings.

  If the light behaves like waves, why do we get the random spots at low illumination?

  Einstein: The light behaves like both! The photon is interfering with itself! 

  Each photon carries a specific energy. 

  The quantitative relationship between wave behavior and particle behavior:

  Energy of a light particle (photon) = h x c/l

  Comes Thompson, 1898, electron IS a particle. Comes lord Rutherford 1911: Nucleus & electrons. . Comes Bohr, 1912 = save from catastrophe, but not rational. 

DeBroglie, 1919. His suggestion: If light behaves like both particles & waves, why shouldn't particles? 

  At that time the general picture of the atom was that there was a nucleus 

  (found 1911 by Ernst Rutherford, England), and that the electrons orbited the nucleus in 

  certain distances only. For a hydrogen atom that was: 0.05 nm, 0.2nm, 0.45nm, 0.8nm, etc 

  (Niels Bohr, 1912). 

  There were no electrons IN BETWEEN Electrons orbiting a nucleus. 

  DeBroglie asked: Why are there

  no electrons in between? 

  His answer: Because the electrons behave like waves! (Back to "junk piles" picture).

So do they make diffraction patterns?

  If the circumfrance of the orbit fits an integer number of wave crests -

   the electron interferes with itself constructively (like in the "garbage piles" on the

  beach). 

  Otherwise the electron interferes with itself destructively - and there is no electron! (No waves

  between "piles" on the beach).

  The levels of an atom have 1 constructive interference for orbit 1, 2 for 2 , etc.

  Connection between matter (particles) & light (photons): emission from atoms. 

  Whan an electron skips from orbit 2 to orbit 1 a photon is emitted. 

  Question: Given that the energy of orbit 1 is 0 and orbit 3 is 2 x 10-19 Joule, in which part of 

  the spectrum is the emitted photon? Answer: IR.

  Addendum, Historical Perspective :

  Historical overview of the connection of today's class to the uncertainty principle by 

  Werner Heisenberg:

   De-Broglie suggested that the atom's energy levels are related to
  the electron's interference with itself in 1919, while in graduate school. 

  The energy of atomic levels in De-Broglie's model were related to the "wave length" of that
  level by using Einstein's relationship: E=hc/WL for photons.
     In Einstein's special relativity (1905) the momentum is P=Energy/c (Not P=mass x velocity, which

  is the momentum in regular physics). In Einstein's first paper on photons (Same year! 1905)

   P=h/WL.

  (That's what Einstein invented in 1905. This relationship later grew up
  to be known the uncertainty relationship, Heisenberg, 1924, in which: P x WL ~> h/2P , 

  INSTEAD OF EQUALITY)
 

  At the time of DeBroglie, 1919, the atom was described with the Bohr
  model. It was known that the atom had energy levels which are quantized,
  with ANGULAR MOMENTUM h,2h,3h etcetera. DeBroglie used the relationship
  between angular momentum and momentum (Angular momentum is =rxP=rxh/WL, r/WL=1,2,3,...

  where r is the distance of the electron from the nucleus).

  That synthesis led Werner Heisenberg to speculate that the electron-wave
  need not orbit the nucleus in circles (1924). Heisenberg had to find all the possible 3D

  orbits in which the electron may interfer with itself!

  For that purpose modern quantum mechanics was invented, with the principle which was

   known, but not fully used or understood, by Einstein in 1905!