Atomic Particles

1
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

mp 1836 me
2
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

3
What is Light?

• Properties of light
• Reflection, Refraction
• A property of both particles and waves
• Interference and Diffraction
• Youngs double slits
• A Property of Waves Only
• Polarisation
• A Property of Waves Only

4
Classical Physics

• Light is a wave
• Youngs Double Slit Experiment
• Faradays experiments
• Maxwells equations

5
Line-Emission Spectrum
excited state
ENERGY IN
PHOTON OUT
ground state
6
Bohr Model

• e- exist only in orbits with specific amounts of
  energy called energy levels
• Therefore
• e- can only gain or lose certain amounts of
  energy
• only certain photons are produced

7
Bohr Model

• Energy of photon depends on the difference in
  energy levels
• Bohrs calculated energies matched the IR,
  visible, and UV lines for the H atom

6
5
4
3
2
1
8
Other Elements

• Each element has a unique bright-line emission
  spectrum.
• Atomic Fingerprint

Helium

• Bohrs calculations only worked for hydrogen! ?

9
(No Transcript)
10
The Birth of the Quantum

• Max 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

11
Implications of Plancks Law

• The energy levels of the molecules must be
  discreet
• Only transitions by an amount Ehf are allowed
• The implication is that light is discreet or
  quantised

energy
n
energy
4hf 3hf 2hf 1hf 0
4 3 2 1 0
These quantum levels are now known as number
states
12
Photoelectric effect

• When light strikes the cathode, electrons are
  emitted
• Electrons moving between the two plates
  constitute a current

13
Photoelectric Effect

• Explanation
• Einstein 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 hft where ft is the threshold
  frequency for the metal.

14
Louis de Broglie1892 - 1987
15
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,

• Which says that the wavelength of light is
  related to its momentum
• Making the same comparison for matter we find

16
Quantum Theory

• Particles act like waves?!
• The best we can do is predict theprobability
  that something will happen.

Heisenberg Dirac Schrodinger
17
Schrödinger
Erwin
(1887 1961)
The task is not so much to see what no-one has
yet seen, but to think what nobody has yet
thought, about that which everybody sees.
18
Schrodingers cat

• After consultation with Einstein, Schrodinger
  proposed a thought experiment in which he
  highlighted the apparent inconsistencies between
  the so-called Copenhagen interpretation of
  Quantum Mechanics and the reality of macroscopic
  measurements.
• He proposed that a cat be placed in a sealed box.
  The release of a poison is then subject to the
  probabilistic decay of a radioactive isotope. If
  the isotope decays, the poison is released. If no
  decay occurs, the poison is not released.
• The result is that the cat is in a superposition
  of states between being dead, and being alive.
  This is very unintuitive.

19
Quantum mechanics

• Wave-particle duality
• Waves and particles have interchangeable
  properties
• This is an example of a system with complementary
  properties
• The mechanics for dealing with systems when
  these properties become important is called
  Quantum Mechanics

20
The Uncertainty Principle
Measurement disturbes the system
21
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

22
The Uncertainty Principle

• Virtual particles created due to the UP

23
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 should be able to confirm or
  disprove initial hints for Higgs at E115 GeV