Unit 2 - Particles And Radiation Flashcards
Define Specific Charge
The amount of charge per kg something has
What is the equation for specific charge?
Charge/Mass
Which part of the atom does specific charge focus on?
The Nucleus
What is alpha radiation?
A helium nucleus
What is beta radiation?
A fast moving electron
What is gamma radiation?
A high energy electromagnetic wave
What is the role of strong nuclear forces?
This force is required to keep nucleons in close proximity within the nucleus
What are the four fundamental forces?
Gravitational field strength, electromagnetic forces, strong nuclear force and weak nuclear force
When does alpha decay occur?
When the ratio of protons to neutrons is too high
When does beta decay occur?
When the ratio of protons to neutrons is too low
What occurs during alpha decay?
A helium nucleus is released from the nucleus which lowers the ratio of protons to neutrons
What occurs during beta decay?
A neutron becomes a proton as a down quark becomes an up quark and an electron is emitted due to this. An antineutrino accompanies the electron and shares the kinetic energy with it.
What is gamma radiation?
Gamma radiation is a high energy electromagnetic wave which is released from the nucleus and often accompanies alpha or beta radiation but doesn’t change the construction of the nucleus in itself
What is an antineutrino?
Antiparticle of a neutron
When does annihilation occur?
When a particle and its corresponding antiparticle meet
Describe the process of annihilation
When an antiparticle and the corresponding particle collide they annihilate each other and their energy is converted into two photons
Describe the process of annihilation
When an antiparticle and the corresponding particle collide they annihilate each other and their energy is converted into two photons
T/F: An antiparticle has the opposite mass and charge of its corresponding particle
False: the antiparticle has the opposite charge but same mass
What is 1eV equal to?
1.6 x 10^-19 J
Why do the two photons produced during annihilation travel in opposite directions?
To conserve momentum
Do the photons produced through annihilation have the same frequency? Explain
Yes they do because they have the same amount of energy
What is the opposite of annihilation?
Pair production
What happens during pair production?
If a photon has enough energy it produces a particle and an antiparticle
What happens during pair production?
If a photon has enough energy it produces a particle and an antiparticle
Define a photon
A packet of electromagnetic radiation
What speed do photons travel at?
The speed of light: 3 x 10^8 m/s
What particle do light source emit?
Photons
What are the four fundamental forces?
Gravity, electromagnetic, weak nuclear and strong nuclear
What particle experience the electromagnetic force?
Particles with charge
What particles experience the strong nuclear force?
Particles containing quarks
What particle experience the weak nuclear force?
Hadrons and Leptons
What is the exchange particle for the electromagnetic force?
A virtual photon
What is an exchange particle?
A particle that causes an interaction between two other particles by carrying a force between them
What two things does a Feynman diagram show?
Particles before and after an interaction and the exchange particle
What is Newton’s first law of motion?
An object at rest will remain at rest until acted upon by an unbalanced force and an object in motion will remain in motion until acted on by an unbalanced force
What is Newton’s second law of motion?
The acceleration of an object depends on the mass and the force applied
What is Newton’s third law of motion?
For every action there is an equal and opposite reaction
What is the exchange particle for the strong nuclear force?
The virtual pion
Why does the strong nuclear force only act over a very small range?
Because the virtual pion cannot travel very far
What is the range of the attractive strong nuclear force?
0.5fm - 4fm
What is the exchange particle for the gravitational force?
The graviton
What is the exchange particle for the weak nuclear force?
The W boson
What interaction is the weak nuclear force involved in?
Interactions that result in changes to the particles involved .e.g. decay
What should accompany and exchange particle on a Feynman diagram?
An arrow showing the direction
What subcategories can particles be split down into?
Leptons, Hadrons, Baryons, Anti-Baryons and Mesons
What is the main difference between leptons and hadrons?
Hadrons are made up of quarks
What is the difference between a baryon and a meson?
A baryon is made up of three quarks where as a meson is made up of a quark and an antiquark pair
What is a fundamental particle?
One that is not made up of other particles
Why are tau and muon particle uncommon?
They are only produced by collisions in high energy environments .e.g. particle collider or Earth’s upper atmosphere
T/F: Neutrinos have no mass and no charge
True
Why do we use quantum numbers?
They help us to determine how different particle will interact and decay
What is strange about the strange number?
Anti-strange quarks have a strangeness of +1 and strange quarks have a strangeness of -1
What is the quark composition of a positive, negative and neutral pion?
+: u _d
-: _u d
0: d_d or u_u
What is the quark composition of a positive, negative and neutral kaon?
+: u_s
-: _us
0: s_d
T/F: Strangeness always has to be conserved
False: strangeness only has to be conserved in strong interactions, it can change by +- 1 in weak interactions
What 3 things must be conserved in all interactions?
Charge, baryon number and lepton number
Describe how photoelectrons are produced
Photoelectrons are produced when photons of the right energy collide with electrons that are within a sheet of metal, this gives them enough energy to be liberated from the metal
What is the work function?
The minimum amount of energy that electrons need to escape a metal
What does it mean that the photoelectric effect is a ‘one to one interaction’?
This means that all of the energy from one photon is transferred to one electron so that photon must have an energy above the work function to liberate an electron
What happens if a photon has energy higher than the work function?
The electron has the chance of being liberated from the metal and the excess energy will be transferred to the kinetic energy store of the photoelectron
What does it mean to increase the intensity of light?
To increase the number of photons emitted per second
How is the photoelectric effect evidence for the particle nature of light?
The effect can only be achieved if electromagnetic radiation comes in packets rather than a wave
What piece of equipment is used to demonstrate the photoelectric effect?
A vacuum photocell
How does a vacuum photocell work?
The cell consists of a metal attached to one of the electrodes which is called the photocathode and another electrode, the anode. This cell is attached to circuit with a micro-ammeter in it. When light with a high enough frequency is shone at the metal photoelectrons are produced which travel through the vacuum to the anode which creates a potential difference. These electrons will then flow through the circuit which will show a reading on the micro-ammeter
What is stopping potential?
The amount of potential difference needed to stop photoelectrons with the highest possible amount of kinetic energy from reaching the anode
What happens when electrons collide with electrons within other atoms?
The electrons within the atoms become excited (move to higher energy levels) or they are removed from the atom completely
Define excitation energy
The exact amount of energy needed to lift an electron from a lower energy level to a higher energy level
How can we measure the excitation energies of atoms?
We can use a cell (similar to a vacuum photocell) with gas inside. It consists of a heated cathode and an anode. Electrons are attracted to the positive cathode and repelled away from the negative anode so as they move across the cell they pick up kinetic energy. If they have the exact right amount of energy they will collide with electrons in atoms and transfer this energy to them so they will lose the Ek and will not make it to the anode which will result in a drop in current.
Define ionisation energy
The minimum amount of energy required to liberate an electron from the atom
How can we measure ionisation energy?
By using the previous set up we will notice when atoms start to ionise as there will be an increase in current as the ionised electrons are also attracted to the anode
What is another name for energy levels?
Orbitals
How do atoms produce photons?
Excitation is only a temporary situation so when the electrons drop down energy levels again they emit the extra energy in the form of photons
How can spectrums be used to identify atoms?
Because all atoms have different energy levels the photons they emit will have different energies and therefore each atom will have its own unique spectrum (fingerprint)
In a hydrogen atom what series defines transitions to ground state?
The Lyman series
In a hydrogen atom what series defines transitions to N = 1?
The Balmer series
In a hydrogen atom what series defines transitions to N = 2?
The Paschen series
What part of the EM spectrum does the Lyman series emit?
UV
What part of the EM spectrum does the Balmer series emit?
Visible
What part of the EM spectrum does the Paschen series emit?
Infrared
What is a line spectrum?
An emission spectrum consisting of separate and isolated line
Define an emission spectrum
A spectrum of electromagnetic waves that have been emitted by atoms
Define an absorption spectrum
A spectrum that is produced by certain frequencies of light being absorbed by a particular atom
How does a fluorescent tube work?
The tube is filled with mercury gas at a low pressure and when a current flows through the tube the atoms become excited and when de-excitation occurs UV light is produced but this cannot be seen by us so the tube is coated in phosphor which then absorbs this UV which excites the atoms and when phosphor atoms de-excite they produce visible light
What happens when electrons are fired at a slit which is roughly the same size as their wavelength?
They diffract
What is produced by the diffraction of electrons
An interference pattern of bright and dark fringes showing where the electrons have constructively and destructively interfered
What happens to the spacing of the fringes if you increase the speed of the electrons?
The fringes become closer together
When is the de Broglie wavelength used?
The de Broglie wavelength is a function that can be used to determine the wavelength of a particle
What is a good material for diffracting electrons and why?
Graphite: the gaps between the layers and atoms in graphite are a similar size to the de Broglie wavelength of electrons
Why is a circular interference pattern produced when using graphite to diffract electrons?
Graphite is comprised of many crystals. One crystal would produce a diffraction pattern in one plane only but multiple crystals create multiple planes and they are produced symmetrically
