Rutherford fired alpha particles at gold foil and found that most went through, some were deflected nearly through 180 degrees

Indicated a small positive charge at centre, and negative electrons in orbits around the positive nucleus

1.1 discuss the structure of the Rutherford model of the atom, the existence of the nucleus and electron orbits

Rutherford's model could not explain the hydrogen spectrumi.e. that when a gas is heated or an electric current is passed through it, it produces a line spectrum

Bohr's model explained it by stating electrons exist in stationary states and radiate energy when they fall from a higher energy level to a lower one

1.2 analyse the significance of the hydrogen spectrum in the development of Bohrs model of the atom

Electrons exist in stationary states without radiating energyWhen an electron falls from a higher energy level to a lower energy level, it emits energy that is quantised by Planck's relationship:

Angular momentum is quantised and can only take values of

where n is the principle

quantum number

1.3 define Bohrs postulates

Planck explained black body radiation by stating that that is, that the amount of energy in a photon is proportional to its frequency, and that it is quantised according to a constant 'h'

1.4 discuss Plancks contribution to the concept of quantised energy

1.5 describe how Bohrs postulates led to the development of a mathematical model to account for the existence of the hydrogen spectrum:

Ad hoc mixture of classical and quantum physics, it assumed some laws held and others did not

Didn't work for heavier elementsCouldnt explain relative intensity of spectral linesCouldnt explain hyperfine spectral linesSplitting of spectral lines when sample placed in a magnetic field (Zeeman effect) could not be explained

1.6 discuss the limitations of the Bohr model of the hydrogen atom

SpectroscopePower sourceDischarge tube

1.7 perform a first-hand investigation to observe the visible components of the hydrogen spectrum

1.8 process and present diagrammatic information to illustrate Bohrs explanation of the Balmer series

1. Problems with the Rutherford model of the atom led to the search for a model that would better explain the observed phenomenaSaturday, 23 October 20109:47 AM

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series

1.9 solve problems and analyse information using:

1.10 analyse secondary information to identify the difficulties with the Rutherford-Bohr model, including its inability to completely explain: the spectra of larger atoms the relative intensity of spectral lines the existence of hyperfine spectral lines the Zeeman effect

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Matter waves - all particles behaved as waves and could be diffracted and had a wavelength etc.

Explained stability of electron orbitsLed to further developments in quantum mechanics

2.1 describe the impact of de Broglies proposal that any kind of particle has both wave and particle properties

Diffraction is the bending of waves around obstacles or through barriersInterference occurs between waves that have been diffracted

2.2 define diffraction and identify that interference occurs between waves that have been diffracted

Davison and Germer fired electrons onto a Nickel crystal and upon detecting the intensity of electrons reflected, found an interference pattern, providing evidence for de Broglie's hypothesis

2.3 describe the confirmation of de Broglies proposal by Davisson and Germer

Electrons can only exist in stationary states, which are standing wavesStanding waves do not radiate energyNumber of wavelengths is equal to the principle quantum number

2.4 explain the stability of the electron orbits in the Bohr atom using de Broglies hypothesis

2.5 solve problems and analyse information using:

Heisenberg - uncertainty principle:

2.6 gather, process, analyse and present information and use available evidence to assess the contributions made by Heisenberg and Pauli to the development of atomic theory

2. The limitations of classical physics gave birth to quantum physicsSunday, 13 March 201110:32 AM

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That is the uncertainty in momentum and uncertainty in position is greater than or equal to a constant - there is a limit to how precisely the momentum and position of an electron can be known

Heisenberg - uncertainty principle:

No two electrons can occupy the same quantum state of an atom: explained regularity of elements in periodic table

Also predicted neutrino (see later sections)

Pauli - exclusion principle:

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Components of nucleus are nucleons:Proton: positive charge, relative mass of 1Neutron: neutral charge, relative mass of 1.5

3.1 define the components of the nucleus (protons and neutrons) as nucleons and contrast their properties

Chadwick found that when the unknown radiation passed through paraffin wax, protons were emitted which could be detected.

By calculating the velocity of the alpha particles, and the protons, he used the conservation laws of momentum and energy to postulate the momentum and energy of the unknown radiation (neutron)

3.2 discuss the importance of conservation laws to Chadwicks discovery of the neutron

Transmutation occurs when one element changes into another element3.3 define the term transmutation

Natural transmutations: alpha, beta minus and gamma3.4 describe nuclear transmutations due to natural radioactivity

Trying to create transuranic elementsBombarded uranium (heaviest known naturally occurring element) with neutronsResults were confusing - he had discovered fission but did not realise it, was expecting a new element which would then decay

3.5 describe Fermis initial experimental observation of nuclear fission

In beta decay, the mass/energy of the products did not equate to the mass/energy of the reactants

Pauli theorised of a very small, neutral particle (which he called neutron, later called neutrino) which would account for this in beta decay

Therefore, conservation laws would hold

3.6 discuss Paulis suggestion of the existence of neutrino and relate it to the need to account for the energy distribution of electrons emitted in -decay

Gravitational force holding together nucleus is many order of magnitude smaller than electrostatic force

e.g. between two protons: gravitation attraction whereas the electrostatic repulsion

3.7 evaluate the relative contributions of electrostatic and gravitational forces between nucleons

Therefore in a nucleus there must be another force (the strong nuclear force) holding together the composite parts

3.8 account for the need for the strong nuclear force and describe its properties

3. The work of Chadwick and Fermi in producing artificial transmutations led to practical applications of nuclear physicsSunday, 13 March 201110:32 AM

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the composite parts

Very short range (at about the force has effectively zero effect)Attractive to a point but after that becomes very repulsiveMuch stronger than the Coulomb force between two protons (~ 10,000 N for the nuclear force)

Properties:

In all nuclei, there exists a 'binding energy', a result of the strong nuclear forceIn nuclear reactions, this results in a 'mass defect', that is, the mass of reactants does not equal the mass of the products, due to ,the equivalence of mass and energy (that is, some of the mass is converted into binding energy)

3.9 explain the concept of a mass defect using Einsteins equivalence between mass and energy

Graphite blocks as a moderatorUranium reactor46 tonnes of natural uranium and uranium oxide interspersed in 40 000 graphite blocksCadmium rods acted as controlled rodsBy withdrawing the cadmium rods he showed that the pile started to heat, the fission reaction had begun

3.10 describe Fermis demonstration of a controlled nuclear chain reaction in 1942

Controlled - every fission should produce only one neutron, others are absorbed by control rods

Uncontrolled - each fission produces 3 more neutrons, which fission 3 more, etc. etc.

3.11 compare requirements for controlled and uncontrolled nuclear chain reactions

Supersaturated alcohol vapour produced using liquid nitrogenIonising radiation attracts alcohol to the ionised particles, leaving 'streams'Alpha are thickest but shortest, then beta are thinner but longer. Gamma rays produce intermittent streams

3.12 perform a first-hand investigation or gather secondary information to observe radiation emitted from a nucleus using Wilson Cloud Chamber or similar detection device

3.13 solve problems and analyse information to calculate the mass defect and energy released in natural transmutation and fission reactions

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Fuel: U-235 or Pu-239Moderator, to slow neutrons (slow neutrons fission better (better chance of being absorbed)) e.g. water, graphite, beryllium, heavy water

Regulator: control rodsCoolant: air, helium, 'heavy' water, liquid sodium, certain organic compoundsRadiation shielding: concrete or similar

Components required

Nuclear reaction produces heat which heats water to produce steam which turns a turbine

4.1 explain the basic principles of a fission reactor

Radioactive tracers in biological or physical systemsAmount of wear in machinery - fractures and thickness problems detected by amount of radiation detected on other side of machine

Regulate thickness of metal or similarUseful for finding leaksIsotopic tracing/scanning Radiotherapy

4.2 describe some medical and industrial applications of radio-isotopes

Neutrons penetrate matter more easily than charged particles Neutrons exhibit wave-particle dualityWhen interacting with matter neutron collides with atomic nuclei and scatters in directions determined by wavelength and structure of the material

X-ray scattering can detect spacing between electron cloudsNeutron scattering can detect spacing between nuclei

4.3 describe how neutron scattering is used as a probe by referring to the properties of neutrons

By accelerating particles to high speeds and smashing them together, the composite parts may be analysed and properties of matter can be known

For example, the LHC is attempting, amongst other things, to find evidence for the graviton or Higgs Boson which is the proposed charge carrier of the gravitational force

4.4 identify ways by which physicists continue to develop their understanding of matter, using accelerators as a probe to investigate the structure of matter

4.5 discuss the key features and components of the standard model of matter, including quarks and leptons

Four forces and their carriers:

Generation Quarks Charge Leptons Charge

I Up +2/3 Electron -1

Down -1/3 Electron Neutrino 0

II Charm +2/3 Muon -1

Strange -1/3 Muon Neutrino 0

III Top +2/3 Tau -1

Bottom -1/3 Tau Neutrino 0

Force Carrier

Gravity Proposed to be Graviton

EM Photon

4. An understanding of the nucleus has led to large science projects and many applicationsSunday, 13 March 201110:33 AM

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EM Photon

Weak Nuclear Force W and K Bosons

Strong Nuclear Force Pion

Manhattan project led to the development of nuclear bombs

Death of millions in proxy warsLed to the cold war

Death of many Japanese at the close of WWIIIncreased understanding of many areas of science e.g. space program

4.6 gather, process and analyse information to assess the significance of the Manhattan Project to society

4.7 identify data sources, and gather, process, and analyse information to describe the use of:- a named isotope in medicine- a named isotope in agriculture

Tc-99m Medicine 6 hours gamma emitter - medical tracerCo-60 (ag) 5.27 years beta minus to Ni-60 - irradiate fruits etc.Ir-190 (eng) 11.78 days beta plus to Os-190 - detect metal thickness

- a named isotope in engineering

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The Hydrogen Spectrum - Balmer's Equation

The wavelength of matter

FormulasSunday, 13 March 201110:35 AM

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