# AQA AS-Level Physics: Particles

What is the standard model?
A theory concerning the four forces - electromagnetic, strong, weak and gravitational.
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What are the two nucleons?
Proton and neutron
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What sub-atomic particle orbits the nucleus?
The electron
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What is the mass number of an element?
The total number of protons + neutrons.
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What is the atomic/proton number of an element?
The total number of protons in that element.
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What is the relative atomic mass?
The average mass of an element compared to 1/12 of a carbon-12 atom.
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How do we calculate specific charge?
Charge(coulombs)/Mass(kg)
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What is a photon?
A chunk of electromagnetic light energy released in discrete packets.
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What are the two equations used to calculate the energy of a photon?
Energy = Planck's constant * frequency OR Energy = (Planck's constant * speed)/Wavelength
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How do we calculate wave frequency?
Frequency(Hz)=Speed(ms^-1)/Wavelength(m)
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How do we convert electronvolts into joules?
Energy in joules = Charge of electrons (1.6x10^-19) * the number of electronvolts
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What is antimatter?
Antimatter is comprised of antiparticles. Antiparticles have an opposite charge, lepton number, baryon number and strangeness to their corresponding particle.
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What is annihilation?
Where particle and antiparticle meet, causing mass to be converted to energy (2 photons).
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How do we calculate the energy produced in annihilation?
Mass * speed of light^2
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How do we calculate the energy of the particles before annihilation?
2*rest energy
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How do we ensure momentum is always conserved in annihilation?
Two photons are produced.
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What is pair production?
Where a single photon of energy is converted into particle and antiparticle pair. In other words, mass is converted to energy.
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In pair production, what happens to the excess energy a photon has?
It is converted to kinetic energy.
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If pair production happens in a magnetic field, what happens to the particle and antiparticle?
They will move in opposite directions due to their opposite charges.
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What is the minimum energy needed for a photon to undergo pair production?
The total rest energy of the two particles.
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Why does pair production always happen near a nucleus?
It recoils to help conserve momentum.
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What are the three types of quarks that we need to know about?
Up, down and strange. All of which have corresponding anti-quarks with an opposite charge, baryon number and strangeness.
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Can quarks ever exist as lone quarks? Why?
No, they cannot. This is because the energy required to pull two quarks apart is so massive that it will result in two new particles.
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Any particle formed of quarks. This includes baryons and mesons.
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What is a baryon?
Any particle which consists of three quarks - such as a proton or neutron.
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What is a meson?
Any particle which consists of one quark and one anti-quark.
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Which baryon is the only stable baryon?
A proton. All other unstable baryons eventually decay into this.
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What are the three products resulting from a neutraon decaying?
A proton, electron and antineutrino.
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Are all mesons unstable?
Yes.
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What are the lightest form of mesons and what are the versions it comes as?
The pion. It can come as π-, π0 and π+.
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List three properties of kaons.
They are heavier and more unstable than pions, they have a much shorter lifetime than pions, they decay into pions, they exist as K0 and K+, they have a strangeness of -1.
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How do mesons and baryons interact?
By the strong force.
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Give two examples of the leptons. What does each lepton have that a hadron does not?
Electron and muon. They each have a corresponding neutrino.
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What is a neutrino?
A chargeless, almost massless particle that is NOT affected by the strong force.
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What are the baryon and lepton numbers of a reaction?
The baryon number is the number of baryons present in a reaction, whilst the lepton number is the number of leptons present in a reaction. They are always conserved.
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What force causes strange particles to be created?
The Strong Nuclear force.
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In what reactions is strangeness conserved/not conserved?
Strangeness is conserved in the strong interaction, but it is not conserved in the weak interaction.
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What is the electromagnetic force and what is its exchange particle?
It is a force that causes an attractive or repulsive force between masses. It acts on charged particles only and its exchange particle is a virtual photon.
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What is the gravitational force and what is its exchange particle?
It is a force that causes an attractive force between masses. It acts on any particles with a mass and its exchange particle is the graviton.
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What is the strong nuclear force and what is its exchange particle?
It is a force which causes an attractive or repulsive force between quarks. It acts upon any particle that contains a quark. Its exchange particle is a gluon between quarks, but a meson between baryons. A pion is also exchanged between two hadrons.
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What is the weak nuclear force and what is its exchange particle?
It is a force that makes particles decay. Its exchange particles are W+ or W- bosons.
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What kind of decay occurs due to the weak force and how does it work?
Beta decay. Alpha decay never occurs due to the weak force. The weak force causes a quark to charge into another type of quark - sometimes resulting in a strange quark.
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What is alpha decay?
Where an alpha particle (helium nucleus) is ejected from the nucleus of an atom.
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What is beta- decay?
Where a neutron in the nucleus changes into a proton and releases a fast moving beta particle (an electron) and an antineutrino.
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What is beta+ decay?
Where a proton in the nucleus changes into a neutron and releases a positron and neutrino
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In a Feynman diagram, what is found on the top, bottom, left and right?
Bottom = reacting particles. Top = products. Right = Leptons. Left = Baryons.
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How can we tell which boson to use for a Feynman diagram?
W- boson is where the junction is going from a neutron to proton. A W+ boson is used when the junction is going from proton to neutron.
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Why do we need neutrinos?
To conserve lepton number.
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## Other cards in this set

### Card 2

#### Front

What are the two nucleons?

#### Back

Proton and neutron

### Card 3

#### Front

What sub-atomic particle orbits the nucleus?

### Card 4

#### Front

What is the mass number of an element?

### Card 5

#### Front

What is the atomic/proton number of an element?