Particles and quantum phenomena Flashcards
What is the atomic mass unit?
1/12th of the mass of carbon
What is the role of the strong nuclear force within the nucleus?
Between 0.5-3 fm the strong force is attractive and counteracts the electrostatic repulsion of the protons keeping the nucleus together.
Below 0.5 fm the strong force is repulsive stopping the neutrons from being pushed together.
What is the equation for alpha decay?
Nuclei X releases an alpha particle becoming Nuclei Y with A-4 , Z-2
What happens in a beta minus decay?
In a neutron rich nuclei, a neutron turns into a proton
What antiparticle properties are the same for their particle?
Rest energy and mass
ALL OTHER PROPERTIES ARE OPPOSITE
What is the mass of a neutrino?
ALWAYS NONE
How did beta decay experiments lead to the hypothesised existence of the neutrino?
After observing electron energy levels, it was discovered that energy was not conserved. This was because the energy is shared between the electron (beta particle) and neutrino.
What is Annihilation?
Annihilation is where a particle and anti particle collide, their masses are converted too energy. This energy and the kinetic energy is released as two photons moving in the opposite direction to conserve momentum.
What is an example of annihilation?
PET Scanners
What is pair production?
A photon is converted into an equal amount of matter and anti matter.
This can only occur when the photon has at least the energy of the two masses. Any excess energy is converted into the kinetic energy of the particles.
What are the four fundamental forces?
Gravitational, Strong, Weak and Electromagnetic
What is the minimum energy required for pair production?
The photon has at least the energy of the two masses. Any excess energy is converted into the kinetic energy of the particles.
What is the exchange particle for the strong interaction, what is its range and what particles does it act upon??
The gluon, 3 fm, Hadrons
What is the exchange particle for the weak interaction, what is its range and what particles does it act upon?
W boson + or - , x10^-18 and all particles
What is the exchange particle for the electromagnetic interaction, what is its range and what particles does it act upon?
Virtual photon, Infinite and charged particles
What is the range of gravity and what particles does it act upon?
Infinite range and acts on any particle with mass
What is a hadron?
Particles formed of quarks that experience the strong nuclear force
What is a lepton?
Fundamental particle and so cannot be broken down any further and do not experience the strong force
What is the only stable baryon?
Proton
What is a baryon?
A particle made up of a series of 3 quarks
What is a meson?
A quark, anti-quark pair
What is a pion?
Non strange meson
What do pions decay too?
Leptons
What do kaons decay too?
Pions
What is a kaon?
Meson with a strange particle
What is a muon and how does it decay?
A ‘Heavy electron’ (lepton) that decays into an electron
What is a strange particle and how is it performed/ decay?
A particle produced by the strong interaction that decays by the weak interaction
What must be conserved in all particle interactions?
Baryon number, Lepton number, Energy, Momentum and Charge
When is the strangeness in a particle interaction not always conserved?
The weak interaction
When is the strangeness in a particle interaction always conserved?
The strong interaction
Why does particle physics rely on large international multidisciplinary teams to validate new knowledge?
Particle accelerators must be built to investigate particle physics which are expensive to build and run and produce a lot of data
What’s the quark combination of a proton?
uud
What’s the quark combination of a neutron?
udd
What are the quark combinations of the pions?
anti-up anti-up OR anti-down anti-down 0
anti-up down +
anti-down up -
What are the quark combinations of the kaons?
anti-strange down OR anti-down strange K0
anti-strange up K+
anti-up strange K-
In what kind of interaction is there a change in quark flavour?
The weak interaction
What is the photoelectric effect?
When EM radiation above a certain frequency is incident on the surface of a conductor, electrons may be emitted from its surface.
What is the threshold frequency?
The minimum frequency of incident light required to eject electrons from a material’s surface in the photoelectric effect
What is the work function?
The minimum energy required for an electron too escape a conductive surface
What was the evidence against the wave theory of light?
The photoelectric effect doesn’t work on all frequencies of light which wave theory suggests it should
There would be a time delay between the photons of a lower frequency between first incidence and emission
As intensity increases, the rate of photoemission would increase for all frequencies (it doesn’t)
What is the photon explanation of the photoelectric effect?
The energy arrives in in discrete packets called photons, each interacts with one electron and the energy of each photon is determined by its frequency E=hf.
Why is the kinetic energy in the photoelectric effect equation a maximum?
If the photon absorbed is of a higher energy than required to just free the electron, the remainder becomes kinetic energy of the free electron.
Some electrons require more energy to be freed from the surface because they are deeper beneath it.
What is the equation of the energy of a photon?
E photon = h. threshold frequency + EK max
How does a photocell work?
Light collides with the cathode, electrons are emitted and accelerated towards the anode and they pass across the gap inducing a current in the circuit.
Why does the photocurrent decrease when a negative voltage is applied?
The electrons must do work to cross the gap due to the opposing potential difference. If the electrons do not have enough kinetic energy they will accelerate away from the negative anode and not all will cross the gap.
Why does the photocurrent reach a saturation current when a positive voltage is applied?
The anode is positive and initially not all the electrons make it across the gap. As the Ve across the gap increases, the number of electrons across the gap increases to a maximum inducing a maximum current.
What is the equation for the maximum kinetic energy of an electron in a photocell?
Ek max = e . Vs
What is the stopping potential?
The potential difference across an anode/cathode gap that means electrons can no longer pass it as the work done too cross it is larger than the EK max of the particle.
What are the conditions for an electron to be able to pass across a photocell?
The EK of the electron > Vs . e
Where Vs is the stopping potential
How does intensity of incident light effect the photo current induced?
Higher intensity, more photons incident per second. One: One interaction so more electrons released per second and a higher current induced (higher rate of exchange of charge)
How do you find the work function from a KE against frequency graph?
hf = work func + EK
mx = c + y
The work function is the extrapolated y intercept
What is the definition of an electron volt, and its value in joules?
The energy gained by an electron moving across a potential difference of 1 volt
1.6 X 10 ^-19
What are atomic energy levels?
The electrons in an atom can occupy finite number of discrete values of total energy, energy levels
What can be said about the energy levels of different elements?
The energy levels of elements are unique
What is the ground state?
The lowest energy level
What is ionisation?
The addition or loss of an electron giving the atom an overall charge
What is excitation?
When an electron gains the exact energy required to change between levels, the electron becomes excited and moves up that energy level.
What is de-excitation?
An electron jumps back down to its original energy level and emits a photoelectron with the same amount of energy as the difference between the two energy levels.
What is thermionic emission?
The release of electrons from a heated material when thermal energy overcomes the material’s work function
How does a gas discharge tube work?
Tube containing a gas at low pressure. When a high potential difference is applied across two electrodes (the cathode and anode), electrons are emitted from the cathode and travel towards the anode. As these electrons collide with gas atoms, they excite the atoms, causing them to emit energy in the form of visible light.
How is an emission spectrum formed?
As an electron deexcites from different energy levels, photons with different amounts of energy, frequency and therefore colour are released.
What does an emission spectrum look like?
For a single element, not a continuous spectrum as only light of specific frequencies and specific colours are produced.
For a mixture, continuous as an array of different energy levels (they are unique too elements)
How can you compare an emission and absorption spectrum?
The energy levels are the same, the lines in the emission spectra of an element are in the same position as the black lines in the absorption spectra of the same element.
How is an absorption spectrum formed?
When photons of light pass through a gas, the photons with the same energy as the energy gaps in the atoms can be absorbed.
How does a fluorescent tube work?
Electrons through tube collide with mercury atoms
Excite, de-excite and release UV photons Absorbed by phosphorous coating
Excites and deexcites releasing visible light.
What is fluorescence?
Phenomena where light is absorbed by an orbital electron and light of a longer wavelength is emitted
What is evidence for the wave nature of light?
Interference patterns and diffraction (Young’s double slit)
What is evidence for the particle nature of light?
Photoelectric effect
What is evidence for the wave nature of electrons?
Electron diffraction
What is the appearance of an electron diffraction pattern?
Concentric rings
How does the momentum of the electrons affect the diffraction pattern?
Increases the DB wavelength so diffracts at larger angles
ALTHOUGH
The gaps they pass through must be a similar size too their DB wavelength too diffract so works up to a certain point.
What is evidence for the particle nature of electrons?
Electron guns (used in electron diffraction) as utilises thermionic conductors which follow particle behaviour (discrete energy packets)
What needs to happen before a new theory is accepted?
Peer review and experiment (validation)
