Particle and Quantum phenomena notes

Notes from unit one of AS AQA Physics A.

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Particle physics and quantum phenomena notes
Atomic structure.
There have been several models used for the atom. The first was the plum pudding model which
has since been proved incorrect. Another is the Rutherford model which is the most used one
today. This was found using the alpha scattering experiment.
In physics, the following Atomic/nuclear notation is used:
Here A representsNucleonsand is the number of particles in the nucleus. Here Z is the atomic
Also, the following values are given for the masses and charges of the sub atomic particles.
Particle Charge (C) Mass (kg)
neutron 0 1.67 x 10
-19 -27
proton 1.6 x 10 1.67 x 10
-19 -31
electron 1.6 x 10 9.11 x 10
To work out the specific charge of the nucleus use the following equation:
Specific charge = Total charge within nucleus (c)/Total mass in nucleus (kg)
Specific charge = Q/M
For example, in an oxygen 16 nucleus:
8(1.6 x 10 )
16(1.67 x 10 )
: 4.79 x 107
Strong nuclear force and Unstable/stable atoms
Isotope: an isotope is an atom of the same element where there is the same number of protons
but a different number of neutrons.

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Strong nuclear force
This is the force that holds the nucleus together.
Given that the nucleus is comprised of positively charged particles, you would expect that it
would fall apart-this is not the case. Although the strong electromagnetic force causes the protons
to repel each other, an either stronger force of attraction causes the protons to get closer
A strong nuclear force over comes the strong electromagnetic force which is repelling the protons
away from one another to form a nucleus.…read more

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As well as this, this radiation particle is emitted when a proton is disintegrated into a nucleus, a
positron and a neutrino.
Particles and antiparticles
Every particle has an antiparticle. This is a particle which is equal in mass, size and density, but is
opposite in charge.
When a particle and antiparticle collide, they destroy each other and release energy. This is know
as annihilation.…read more

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The mass of each particle is equal to :
E= 1.67x10-27
x (3x 108
E=1.5x 10-10 J
This gives a total energy of 3x10-10
J and suggests that each photon has 1.5 x 10-10 J of energy.
This can then be subbed into the formula: E=hf, to find the frequency the photon would be
travelling at. This gives the following:
Energy= planck constant x frequency
Frequency =energy/planck constant
/6.63 x 10-34
f= 2.…read more

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Different wavelengths and frequencies give the waves different properties. Increases and
decreases in amplitude (height of the sine wave from the contant) also alter the property of the
wave. This is covered more in unit 2
Every electromagnetic wave travels at the speed of light which is 3 x108 .…read more

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Photons are explored more in the section about photoelectricity and photon theory.
Particle sorting
All matter in the universe can be categorised into two catergories: Hadrons and Leptons
Hadrons are particles and antiparticles which can interact through strong interaction
These include Baryons and mesons. Baryons are particles which contain three quarks and decay
into protons. Baryons are protons and neutrons. Mesons do not decay into protons and consist of
a quark and antiquark pair. Mesons are pions and kaons.…read more

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In all interactions between particles, lepton numbers much be conserved. In terms of simple
lepton numbers, a 1 is awarded to leptons, a -1 is awarded to antileptons and a 0 is awarded to
non- leptons.
However, lepton numbers are far more complex than this. Lepton numbers are divided amongst
each flavour of lepton, and the corresponding neutrinos. This means lepton numbers must be
conserved for the individual flavours of leptons. These are taus , muons and electrons.…read more

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In terms of quarks this is
Udd uud + e +
The d quark changes to a u quark, and a beta particle and an electron antineutrino are released to
conserve the baryon number. As well as this, the full lepton number is conserved at a lepton has a
value of 1 and an antilepton has a value of -1, provided these are of the same flavour of lepton.
Conservation of Baryon number
In all particle interactions, Baryon numbers must be conserved.…read more

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Photo electricity
The photoelectric effect is used to prove the wave-particle duality of electromagnetic waves.
The photoelectric effect is where electrons are emitted from the surface of a metal when
electromagnetic radiation is directed at it. At AS we look specifically at Light. There several factors
which influence photoemission:
The incident electromagnetic radiation must be above a certain frequency. This value of
frequency means that planks constant multiplied by frequency is equal to the work
function.…read more

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Each conduction electron absorbs a photon. If this photon has enough energy and exceeds the
work function, the electron will escape from the metal surface. If it does not, the electron will
collide with the ions of the metal to dexcite from the excited state it is in from absorbing a photon.
Collisions of electrons with atoms
Adding or removing electrons from an atom will a negative or a positive ion.
Ionisation energy is measured by colliding electrons with atoms of a gas.…read more


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