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The end of classical physics:
photons, electrons, atoms
Last time:
Discovery of the electron: Charge quantization
photo-electric effect: light behaves as a particle
Discovery of the nucleus: Rutherford scattering experiment
Today:
Atomic spectra: emission and absorption. Evidence for atomic energy levels
Bohr’s model of the hydrogen atom
Continuous emission: black-body radiation
Phhoto-electric effect:


The energy transfer
is all or nothing
process in contrast
to the classical
theory of continuous
transfer of energy
eV0 = Kmax = hf –E0
Rutherford’s model



Continuous spectrum
Then the electron FALLS into the nucleus: catastrophe !
But this doesn’t happen => the catastrophe is in classical
physics !
Atomic spectra: emission and absorption



Spectra are discrete
Different atoms have
different lines
Absorption and emission
spectra are NOT the same
Hydrogen atom: Bohr’s model


Stable orbits, with
distinct quantum
numbers n= 1,2,3…
Angular momentum
is quantized :
Emission and absorption

Balmer found ( by trial and error) :
1
1 1
 R( 2  2 ), n  3, 4,5,...

2 n