2: Particles and Radiation Flashcards
What can be used as evidence for discrete energy levels?
-Emission and absorption spectra as lines appear at discrete points
-Shows photons of specific frequency have been absorbed/emitted
-Shows electrons can only absorb an exact amount of energy to be excited
How do we validate changes in the scientific community?
-Evaluated by peer-to-peer review
-This increases legitimacy and checks for errors
How does a fluorescent tube work?
-High voltage is applied across mercury vapour which accelerate the free electrons
-The electrons then collide with the mercury atoms
-Mercury electrons are excited and move to higher energy levels
-Electrons then de-excite to release a UV photon
-Phosphorous coating absorbs UV photons and its electrons are excited and then de-excite to release visible light photons
State a use of radioactive isotopes
Can be used to carbon date objects to estimate their age
What is de Broglie wavelength?
Wavelength = Planck’s constant/Momentum
Diffraction occurs when wavelength and the distance of the gap are of the same order of magnitude
What is wave particle duality?
The idea that light can be viewed as either a wave or a particle
Electron diffraction suggest wave behaviour due to interference pattern produced
Photoelectric effect suggests particle behaviour due to energy being dependent on frequency not intensity
How do we calculate for line spectra?
hf=Ef-Es
Where Ef is the energy level an electron ends up at and Es is the energy level it starts at
To convert to eV multiply by (1.6)*10^-19
What are emission spectra?
Lines showing various energy states an electron can occupy
An electron gains energy in a collision and is excited to a higher energy level
The electron then de-excites and releases a photon
Photons give up all energy, electrons only give up some
How does the photoelectric effect work?
A photon collides with a surface electron and transfers its energy in a one to one interaction
The electron is then released if it has energy greater than or equal to the work function of the metal
What are the exchange particles?
Electromagnetic: Virtual photon
Weak: W+/W-
Strong: Pion
What is annihilation?
When a particle and its antiparticle equivalent collide to produce two gamma photons
What is conserved in particle interactions?
-Energy
-Momentum
-Charge
-Baryon/Lepton number
-Strangeness(Only for strong)
What is strangeness?
Only exists in kaons
Must be conserved only in strong interactions and can change in weak interactions
What are leptons?
Leptons are fundamental particles
Muons are heavy electrons and decay into electrons
What is pair production?
When one gamma photon splits to produce an electron and a positron
What is a photon?
A particle used to represent light
Its energy equates to its frequency multiplied by Planck’s constant
What is an antiparticle?
A particle with the same mass, same rest energy
But opposite charge and opposite lepton/baryon number
Why was the neutrino proposed as a particle?
A range of energies were seen during beta-plus decay
The energy of the beta particle was fixed so an extra particle must be there to carry off the rest of the energy
This particle must be neutral charge to conserve charge
What is beta minus decay?
The emission of an electron and production of an antineutrino
A neutron is converted into a proton
What is alpha decay?
When a nucleus emits a particle consisting of two neutrons and two protons-equivalent to a helium nucleus
What is the strong force?
A force that only affects hadrons
It is attractive up to 3fm and repulsive below 0.5-0.8fm
The strong force keeps the nucleus together
Describe the composition of hadrons
A proton is uud
A neutron is udd
Mesons are a quark-antiquark pair
Pion0= up-antiup or down-antidown
Kaon0= down-antistrange or strange-antidown
What are hadrons?
A group of particles consisting of baryons and mesons
Baryons are made up of three quarks and decay into protons
Mesons made up of a quark-antiquark pair and kaons decay into pions
Only hadrons experience the strong force
What is an isotope?
An atom with the same number of protons/electrons but a different number of neutrons
What is the work function?
The minimum amount of energy an electron must have to be released from the surface of a metal
What is the threshold frequency?
The minimum frequency a photon must have to release an electron from the surface of a metal
What is specific charge?
The ratio of the charge of a body to its mass
What are the equations for the photo electric effect?
hf = Φ + Max Ek
hf = Φ + (1/2)mv^2
hf = Φ + e.Vs (stopping potential)
Information that can’t be put on flashcards
-Model of an atom
-Feynmann Diagrams
-Nuclei notation
-Quark Quantities
