Particles Flashcards
What is the Thompson Model?
Atoms were spheres of positive charge with tiny negative electrons stuck in them like a plum pudding
What were Rutherford’s experiments?
A stream of α particles where fired at thin gold foil, this was used to disprove Thompson’s model
What did Rutherford’s experiments prove?
Most of the particles went through the foil = particles were mostly empty
Some particles deflected at large angles = positively charged nucleus
Some particles were deflected at obtuse angles = the nucleus must be much smaller than the atom
What is the charge of an electron?
1.6x10-19 C
How does Flemming’s left-hand rule relate to circular motion?
The force on a charged particle from a magnetic field always acts perpendicular to the particles direction causing circular motion
F = Bqv and F= mv^2/r
What formula relates the momentum (or mass and velocity) of a charged particle in a magnetic field to the radius of its path?
r = mv / Bq
ρ = mv
What’s a cyclotron?
A device made of 2 semicircular electrodes with uniform magnetic fields applied perpendicularly to the electrodes upon an electron using an alternating current
How does a cyclotron work?
A p.d is induced across the electrodes and a particle is fired into it
P.d causes the particle to accelerate
The increases in speed cause the radius of the increase
The potential difference is reversed so that it continues to accelerate
What’s an electron volt?
1ev= 1.6x10^-19 J
1J = 6.25x10^18 ev
What’s a linac?
A linear particle accelerator
How does a linac work?
Electrodes are connected to an alternating supply so the charge of the electrode constantly switches between + and -
The rate of alternation is timed so that the particle is always attracted to one electron and repelled by the other
The electron speeds up and to compensate for this the length between the electrons increases.
How does an electron gun work?
Heat a negative metal electrode until thermionic emission occurs
Fire the electron at the cylindrical anode with a whole in it
What are hadrons?
Non-fundamental particles made of quarks
What are the two types of hadrons?
Baryons and Mesons
What are baryons?
Protons and Neutrons ect… with baryon number 1
What is the only stable baryon?
Proton, as the neutron can decay into a proton
What are mesons?
Unstable hadrons with a baryon number of 0
What are leptons?
Fundamental particles that cant be made any smaller
3 maian types of letpons?
Electrons, Muons, Tau (the other 2 weird ones are basically just heavy electrons)
What is a neutrino?
A particle that has no charge represented with ν “nu”
What is the lepton rule for these particles?
They all have a lepton number of 1, but they are all counted separately
What’s an antiparticle?
A particle with equal mass, but the reverse of the charge and lepton/baryon number
What is the mass and energy equivalence formula?
E = mc^2
What does the energy equivalence formula show?
That matter can be created from energy
What is the rule for when matter is created?
When matter is created an equal amount of antimatter must also be created
What is annihilation?
When a particle and antiparticle collide all matter is exchanged for energy
What are quarks?
The building blocks for hadrons
Types of quarks?
up, down, strange
top, bottom, charm
What quarks are used to make protons and neutrons?
only the up and down quarks
QUARK TABLE
QUARK TABLE
What properties must be conserved in particle interactions?
Energy and momentum
Charge
Baryon Number
Lepton number
How does particle detection work?
Charge particles leave a track of ionisation that can be detected and recorded
How does a cloud chamber detect particles?
Using a supercooled vapour, ions left by the particles condense leaving tracks
Thicker traces mean more ionisation
ONLY SHOWS CHARGED PARTICLES
How do bubble chambers detect particles?
Hydrogen is kept as a liquid above its boiling point by pressurizing it
Ionisation by charged particles causes a reduction in pressure in some parts causing bubbles
How can magnetic fields be used in particle detection?
Magnetic fields cause a particle to deflect in circular motion.
Positive particles follow the opposite direction to Flemming’s left hand rule
When do neutral particles show up?
Only upon decaying or interacting with a charged particle
