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Dr hab. EWA POPKO
www.if.pwr.wroc.pl/~popko
Room 231a, A-1
Modern Physics
Manuals
Young and Freedman, „University Physics”, Chapters 39-46
Addison – Wesley Publishing Company, 2000
Lecture I
Based on the lectures by Lynn Cominsky and Jeff Forshaw
Syllabus
Lec 1 Corpuscular- waves dualism of light and matter. Planck's Law. De Broglie postulate. The Heisenberg uncertainty principle.
2
Lec 2 Tunneling effect. 1Lec 3 Hydrogen Atom. Quantum numbers. Spin. Many-electron atom. Absorption
and emission spectrum. 3
Lec 4 Postulates of quantum mechanics. Wave function.The Schrodinger Equation and its application (potential well, scanning tunnelling microscope). 2
Lec 5 Quantum statistics: Fermi-Dirac and Bose-Einstein. Lasers. 2
Lec 6 Molecular bonding and in a solid state. Crystal structure of solids. Band pass model of solids.
2
Lec 7 Electro-optical properties of metals, insulators, semiconductors and the superconductors.
2
Lec 8 Selected modern semiconductor devices (solar cell, semiconductor laser, photodiode).
1
Total hours 15
Atomic Particles
Atoms are made of protons, neutrons and electrons
99.999999999999% of the atom is empty space Electrons have locations
described by probability functions
Nuclei have protons and neutrons
nucleus
mp = 1836 me
Atomic sizes
Atoms are about 10-10 m Nuclei are about 10-14 m Protons are about 10-15 m The size of electrons and
quarks has not been measured, but they are at least 1000 times smaller than a proton
What is Light?
Properties of lightReflection, Refraction
A property of both particles and waves Interference and Diffraction
Young’s double slitsA Property of Waves Only
PolarisationA Property of Waves Only
Classical Physics
Light is a waveYoung’s
Double Slit Experiment
Faraday’s experiments
Maxwell’s equations
0
00 0
0
1
E
B
BE
t
EB J
t
The Birth of the QuantumMax Planck
The energy contained in radiation is related to the frequency of the radiation by the relationship
n is a positive integer called the quantum number f is the frequency of the oscillation
A discreet packet of energy, later to become known as “a photon”
nhfE
Implications of Planck’s Law
The energy levels of the molecules must be discreet
Only transitions by an amount E=hf are allowed
The implication is that light is discreet or quantised
These quantum levels are now known as number states
43210
energy4hf3hf2hf1hf0
energy n
Photoelectric effect
When light strikes the cathode, electrons are emitted Electrons moving between the two plates constitute a current
Photoelectric Effect
ExplanationEinstein: the quanta of energy are in fact
localised “particle like” energy packets Each having an energy given by hf Emitted electrons will have an energy given
by
Where f is known as the “work function” of the material
hfKmax
Properties of matter
Consists of discreet particles Atoms, Molecules etc.
Matter has momentum (mass)A well defined trajectoryDoes not diffract or interfere
1 particle + 1 particle = 2 particles
Louis de Broglie1892 - 1987
Wave Properties of Matter
In 1923 Louis de Broglie postulated that perhaps matter exhibits the same “duality” that light exhibits
Perhaps all matter has both characteristics as well For photons,
h
c
hf
c
Ep
mv
h
p
h
Which says that the wavelength of light is related to its momentum
Making the same comparison for matter we find…
Quantum Theory
Particles act like waves?!The best we can do is predict the
probability that something will happen.
Heisenberg Dirac Schrodinger
Quantum mechanics
Wave-particle dualityWaves and particles have interchangeable
propertiesThis is an example of a system with
complementary properties The mechanics for dealing with systems
when these properties become important is called “Quantum Mechanics”
Measurement disturbes the system
The Uncertainty Principle
The Uncertainty Principle Classical physics
Measurement uncertainty is due to limitations of the measurement apparatus
There is no limit in principle to how accurate a measurement can be made
Quantum Mechanics There is a fundamental limit to the accuracy of a
measurement determined by the Heisenberg uncertainty principle
If a measurement of position is made with precision Dx and a simultaneous measurement of linear momentum is made with precision Dp, then the product of the two uncertainties can never be less than h/2p
xx p
The Uncertainty Principle
Virtual particles: created due to the UP
E t
In Search of the Higgs Boson
Higgs boson is “cosmic molasses” – the Holy Grail of particle physics
Interactions with the Higgs Field are theorized to give all the particles their masses
LHC detectors have confirmed or disprove initial hints for Higgs at E=115 GeV
Confirmed 2013, Nobel 2014
