Transcript Transparancies for Revision Lecture - University of Manchester

Quantum Phenomena
II:
Revision
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Atomic Structure
Hydrogen atom
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Quantum numbers
Electron intrinsic spin
Other atoms
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More electrons!
Pauli Exclusion Principle
Periodic Table
Fundamental Physics
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Particle Physics
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The fundamental particles
The fundamental forces
Cosmology
The big bang
 The evolution of the
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universe
http://ppewww.ph.gla.ac.uk/~parkes/teaching/QP/QP.html
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April/May 2003
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Chris Parkes
Quantum Numbers
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Atom can only be in a discrete set of states n,l,m
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Principle n fixes energy - quantized
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Integer in range 0 to n-1
m (or ml ) fixes z component of angular
momentum
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2
Integer >=1
l fixes angular momentum L
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Diff. From classical picture with any orbit
Integer in range –l to +l
Total Angular momentum
1.
Orbital angular momentum L, e orbiting nucleus
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2.
Quantum number l
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3.
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Has ms =-1/2, +1/2
So splits an l state into two
Total Angular Momentum J
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3
Interacts with magnetic field, U=mlBB
Zeeman effect gives splitting of states
Spin s=1/2, intrinsic property of electron
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5.
notation l=spdfg…., l=0,1,2,3,4…
l has z-component ml, (-l….+l)
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4.
L2=l(l+1)h
Sum of orbital and spin
Anomalous Zeeman effect / Stern-Gerlach Expt
Energy levels
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Hydrogen Energy levels  1/n2 , scale is eV
 13.6
E
eV
2
n
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In a magnetic field E will depend upon other
quantum numbers (ml,ms), for Zeeman effect this
is:
U  ml  B B
[For anomalous zeeman effect from electron spin it is
U   gms  B B
Where g is gyromagnetic ratio ~ 2]
4
Energy Levels cont..
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For multi-electron atoms
Energy splitting depends on l even in absence of
magnetic field.
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occurs due to screening effect
Central field approximation
electrons
nucleus
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Pauli Exclusion principle
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5
No two fermions in same state
…Structure of Periodic table
Particle Physics
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Forces are due to exchange of the fundamental
force carrying bosons
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Know the fundamental particles
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Energy, momentum, electric charge
Baryon number, lepton number
Particle interactions can be written as Feynman
diagrams
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6
Confined in colourless hadrons
Added some more conservation laws
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Three generations of quarks and leptons
Don’t observe free quarks
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Photon,gluon,W+,W-,Zo (and presumably graviton)
Know the basic vertices, and conservation laws to see
whether or not a reaction will occur.
Particle interactions
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7
Some basic standard model vertices:
The Big Bang
Evidence for the Big Bang
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It is dark at night! See Olbers Paradox
Universe expanding
Cosmic microwave background
Relative abundance of elements in universe
Universe Expanding – Hubble’s law
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v
=
Velocity
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8
H
Hubble const.
x
d,
distance
Hence universe ~ 15 billion years old
Evolution of the universe
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Controlled by Quantum Phenomena
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Early stages dominated by basic particle physics
Later stages by gravitational effects
Starts at high temp., high density
Cools down and expands….
Key stages
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Separation of forces into the four basic forces
Formation of nuclei
Formation of atoms
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9
Microwave background radiation, remnant photons from when
atoms formed
Then gravitation dominates and stars and galaxies form