From the Atom to the (i forgot) Flashcards
The (major) steps of the Big Bang:
1. ?
1. Universe in a singularity, energy and mass same thing VERY hot (and it cools)
The (major) steps of the Big Bang:
2. ?
- Matter-Antimatter ‘war’, matter won (somehow)
Gravity leaves
The (major) steps of the Big Bang:
3. ?
- Strong nuclear leaves
The (major) steps of the Big Bang:
4. ?
- All four forces split
Sea of radiation (fundamental particles)
Too hot for nucleons to form
The (major) steps of the Big Bang:
5. ?
- Protons and neutrons form
Sea of radiation still
The (major) steps of the Big Bang:
6. ?
- Atoms (deuterium) can now form (nucleosynthesis)
Deuterium can also form helium
The (major) steps of the Big Bang:
7. ?
- Light is seen (photons trapped in matter)
Stars, planets and galaxies can now form
Evidence for the Big Bang?
- Cosmic background radiation
- Expanding universe
- 75% hydrogen, 25% helium
- Formation of stellar structures
Evidence for expanding universe by Hubble?
- Red shift of elements compared to lab results
2. Estimation of distance with luminosity
What do the two axes on a H-R diagram represent?
Luminosity
Temperature
What is the order of temperature in a H-R diagram?
OBAFGKM
hottest) Oh Be A Fine Girl Kiss Me (coolest
Where do 90% of all stars lie?
The Main Sequence
Stars with greater mass are brighter because?
To counter the great mass they have, they need more energy which makes them bigger and brighter
Above the Main Sequence, there are?
Giants and supergiants
Below the Main Sequence, there are?
Dwarves
The steps of star formation:
1. ?
Hydrogen gas clusters
The steps of star formation:
2. ?
Gas contracts into dark cloud
The steps of star formation:
3. ?
Gravity potential converted into heat (eventually nuclear reactions)
Protostar forms and the mass spins
The steps of star formation:
4. ?
Fusion starts
Debris gets knocked off
The steps of star formation:
5. ?
Main sequence star is formed
What is stellar equilibrium?
The balancing of the force of energy pushing out and the gravity pushing in for stability
What is a common feature between all main sequence stars?
They use hydrogen (proton-proton) fusion whereby 4 protons form helium and energy
What are the two types of fusion possible by main sequence stars?
- Proton-proton chain
- CNO cycle (for stars hotter than 1.8x10^7)
The steps of star death (for x < 8 SM):
1. ?
Small, duller, yellowish, warm sun (like ours)
- proton-proton fusion
The steps of star death (for x < 8 SM):
2. ?
Red giant
- helium fusion (when hydrogen depletes)
The steps of star death (for x < 8 SM):
3. ?
Helium flash
- will have hydrogen, helium, carbon-oxygen core
- star contracts into core and expands
The steps of star death (for x < 8 SM):
4. ?
White dwarf (and planetary nebula)
- oxygen and carbon core
- cannot fuse (not hot enough)
The steps of star death (for x > 8 SM):
1. ?
Big, bright, blue, hot sun
- CNO cycle
The steps of star death (for x > 8 SM):
2. ?
Red giant
- core (from out to in): helium, carbon, oxygen, neon, silicon, iron
The steps of star death (for x > 8 SM):
3. ?
Supernova
- Star contracts and then explodes
The steps of star death (for x > 8 SM):
4. ? (for core mass < 1.4 SM)
Neutron Star
- Very dense, composed completely of neutrons
The steps of star death (for x > 8 SM):
4. ? (for core mass > 1.4 SM)
Black hole
- Single point of infinite density (singularity)
What were the 6 William Crookes’ observations about the cathode rays?
- Can appear from any surface
- Green fluorescent light
- Travel in straight lines
- Deflected by magnets
- Has energy and momentum
- Can cause chemical reactions
What did the Maltese Cross prove?
Cathodes travel in straight lines i.e. don’t diffract
they are particles not waves (for now…)
What did the Paddle Wheel prove?
They have energy and momentum
What did J.J. Thompson figure out with cathode rays and how?
the charge:mass ratio q/m using qvB = mv^2/r with electric and magnetic fields
What model of the atom did J.J Thompson make?
Plum pudding model, where the electron ‘plums’ were in a sort of positive ‘dough’
What did Milikan figure out with q/m?
The charge and thus mass of an electron, by making mg = qE with terminal velocity of an oil driblet (and v depended on mass and radius),
He concluded that charge is quantised
What was the Thompson model supposed to predict that?
The deflections would be minimal due to the whole atom being in positive and pass straight through as the charges (of the atoms) cancelling out would be too weak to affect the alpha particles
What did the Gold Foil Experiment show?
Most alpha particles went through the foil but 1/8000 got deflected over 90°
What model of the atom did Rutherford make?
Rutherford model, where the atom is mainly empty space that has electrons floating around and a tiny dense positive nucleus
What were the issues with the Rutherford model?
- Rutherford did not know how the electrons were arranged around the nucleus
- Rutherford did not know how the electrons moved without creating EMR and losing energy
- Rutherford did not know how the electrons did not collapse into the positive core
The unknown neutral radiation was thought to be gamma, why was it concluded it wasn’t?
Because it could knock protons off of paraffin wax which photons couldn’t do (i.e. it had mass and momentum)
Which two laws of conservation did Chadwick use to find the neutron?
- Momentum (since the proton mass ≈ neutron mass)
- Energy (since it’s elastic, velocity in ≈ velocity out)
Why was the paraffin wax used?
Neutrons could not be detected because they didn’t have a charge while protons (from the wax) could be
What did the inclusion of the neutron in the model of the atom achieve?
- Explained the extra mass of the atom
- Explained how electrons do not fall into the centre (as charges cancel out)
For the Balmer Formula, wavelength of emitted UV photon,
nf = 1 and ni = ?
ni = 2, 3, 4…
For the Balmer Formula, wavelength of emitted UV photon,
nf = ? and ni = 2, 3, 4…
nf = 1
For the Balmer Formula, wavelength of emitted visible photon,
nf = 2 and ni = ?
ni = 3, 4, 5…
For the Balmer Formula, wavelength of emitted visible photon,
nf = ? and ni = 3, 4, 5…
nf = 2
For the Balmer Formula, wavelength of emitted infrared photon,
nf = 3 and ni = ?
ni = 3, 4, 5…
For the Balmer Formula, wavelength of emitted infrared photon,
nf = ? and ni = 3, 4, 5…
nf = 3
What model of the atom did Bohr make?
Bohr Model:
- Electrons are situated around nucleus in ‘stationary states’
- Electrons absorb energy and move up state
- Electrons emit photon and move sown state
- Angular momentum is quantised (nh/2π)
Which two important pieces of information did Bohr use for his model?
- Planck’s quanta
- Balmer equation
- Other data
What were the issues with the Bohr model?
- Mix of classical and modern physics
- Only works for hydrogen
- Could not explain relative intensities
- Could not explain very thin spectral lines
- Could not explain Zeeman effect
What is the Zeeman effect?
The phenomena of spectral lines split in magnetic fields
De Broglie stated that that…
The electrons that orbit the nucleus are actually standing waves (the number of wavelengths corresponding with their electron number), which explain how they move without emitting a photon
The Schrodinger model states that…
- Electrons exist in probability clouds and that they can only be inferred by squaring the Schrodinger equation (a wave function which contains all the info on a particle)
- Orbit position can vary depending on energy of electron (explaining hyperfine lines)
- Denser the cloud → Higher the probability
What was Schrodinger’s contribution to physics?
- Showed the probabilistic (not deterministic) nature of particles and the universe
- Used and improved upon the Bohr model
- Copenhagen interpretation (everything is in a superposition of states until collapsing)
Heisenberg Uncertainty Principle states that…
- The more you know about a particle’s momentum, the less you know about position (and vice versa)
- Set limits on knowledge
Pauli’s Exclusion Principle states that…
No 2 quantum numbers of an electron can have the same quantum numbers (n, l, m1, m2)
This explains how electrons are arranged around an atom
Wave-particle duality states that…
Light behaves like a wave with itself
Light behaves like a particle with matter
De Broglie’s logic for thinking about wave-particle duality with particles is because…
- Waves carry energy
- Matter has energy (E = mc^2)
- Therefore matter must also have a wavelength
What experiment showed wave-particle duality of matter?
The diffraction pattern created from a electrons escaping a vacuum tube crack
What is radiation?
The spontaneous breakdown of an unstable element by the emission of α or β particles or γ-rays
What is a transmutation
The change of element due to its instability and radiation (in alpha and beta decay)
What is alpha decay and what is the formula for it?
The emission of an alpha particle causing a transmutation of the original unstable element
aXz → 4He2 + a-4Yz-2
note number/letter before is atomic mass, after is atomic number
What is beta decay and what are the formulae for it?
The emission of a beta particle causing a transmutation of the original unstable element
β-: aXz → aYz+1 + e + anti-ν
β+: aaXz → aYz-1 + anti-e + ν
What happens to the neutron (in beta minus) and the proton (in beta plus) and what is an important point to note?
Neu → Pro + e
Pro → Neu + p
The neutron is NOT made up of a proton and electron
The proton is NOT made up of a neutron and positron
They simply change forms in beta decay
Because beta decay consists of the release of two particles, what quality will the kinetic energy of the emission have?
Kinetic energy can be shared between the two particles. If an electron has high KE then the neutrino has low KE an vice versa.
This can be demonstrated on a beta spectrum graph, where the KE of an electron is plotted against the probability of an electron with this KE existing i.e. Kinetic energy can vary widely
What is gamma decay and what is the formula for it?
The emission of a gamma particle
- aXz → 4He2 + aXz
- note * *aXz indicates an excited element
Rank speed from highest to lowest
- γ (3x10^8)
- α (2x10^8)
- β (2x10^4)
Rank penetration from highest to lowest
- γ (high penetration)
- β (higher than α penetration)
- α (low penetration)
Rank ionisation from highest to lowest
- α (high ionisation)
- β (lower than α ionisation)
- γ (lower than β ionisation)
‘Rank’ ionisation from highest to lowest
- α (+2)
- β (±1)
- γ (0)
What is the nature of these particles?
α = helium particle β = electron/positron γ = EMR
What is a half life?
The time it takes for mass of a substance to be halved
How can you find how many half lives are in a radioactive substance (Nh)?
Nh = t/th
t = total time th = half life
What is the strong nuclear force?
The very strong force between nucleons that keeps them together in spite of the repulsive electrostatic forces
What does this diagram say about the strong nuclear force?
https://i.stack.imgur.com/Ts7EV.png
- Holds all nucleons together (charged or not)
- Much stronger than electrostatic
- Very limited range, attractive at small distances
- Repulsive at VERY small distances
Explain the band of stability
https://image.slidesharecdn.com/5-151101143038-lva1-app6892/95/58-nuclear-stability-and-halflife-2-638.jpg?cb=1446388282
In order to be stable, atoms at larger atomic numbers must have more nucleons to compensate for electrostatic repulsion.
Define Mass Defect
Mass Defect: The difference between an atom and its components
Why does a mass defect occur?
To create a strong nuclear force to counter electrostatic repulsion, the mass of the constituents must be converted into energy (i.e. SNF), causing a mass reduction
Define Binding Energy (BE)
The energy required to seperate the nucleons of an atom
What is the formula for Mass Defect (Md)
Md = Ac - A
Md = Mass Defect (Au) Ac = Mass of Constituents (Au) A = Atom Mass (Au)
What is Mass Defect equivalent to?
Mass Defect ≡ Binding Energy
E = Md = Parts - Products
What is the formula for converting Kg → Au?
Aur = kgr/(1.661 x 10^-27)
What is the formula for converting Au → MeV?
Aur = 931.5 MeVr
What does Binding Energy per Nucleon (BE/N) measure?
How tightly the nucleons of an atom are placed together and the distribution of BE over all nucleons in an atom
Why are atoms with lower AND higher atomic numbers more unstable and what doe this mean?
For lower: There are not enough nucleons to counter the electrostatic force
For higher: There are too many nucleons where the big radius of the atom causes BE to be distributed poorly among all the nucleons
What element has the highest BE/N, why and what does this mean?
Iron 56, because the atom has a balance of small radius and great energy. To add nucleons would consume energy
As a result Iron can not be easily fused or fissioned, which can be seen in the core of suns where the last product is iron
What do all atoms desire?
To be stable, which it will do at any cost
In order to become stable, unstable lower atoms tend to go through…
Fusion, releasing lots of energy
e.g. H 1
In order to become stable, unstable higher atoms tend to go through…
Fission, releasing lots of energy
e.g. U 238
What is the critical mass?
The point when the production of neutrons equals the loss of neutrons in a fissionable material
What is neutron capture?
The absorbing of a neutron by a nucleus that may or may not result in fission
Name 3 situations in which fission via neutron capture can fail and why?
- Capture without fission
- Capture by other atom or material
- No capture
Very fast neutrons cannot be captured but slowed ones can. How can neutrons be slowed down?
Through moderators, substances which reduce the thermal energy of the neutron
What are the 5 major components of a nuclear reactor?
- core of fuel → fissionable element
- moderator → slows down neutrons
- means of regulating free neutrons → control rods
- coolant → cools reactor
- radiation shielding → reactor and biological shields
What is a fertile material?
An element that can be converted into a fissionable form through neutron capture
E.g. Uranium 238
Reactors are a combination or (what?) and how can chances of fission be increased?
Fissionable and fertile materials. Chances of fission can be increased by increasing the amount of fissionable material in the core
How can a fertile material fail to sustain a chain reaction?
- An impure sample may not accept a neutron, failing to cause neutron capture
- Neutrons may miss because it is too small to hit target
What is the smallest amount of a fissionable substance necessary where a chain reaction is possible?
Critical mass
What do control rods do and how do they do it??
They slow down the rate of fission by absorbing neutrons
By pushing them in, they absorb excess neutrons
By pulling them out, they allow neutrons to initiate more
What are the two types of reaction and what do they look like?
Controlled Reaction: Where only one neutron can hit another atom with excess neutrons being absorbed
Uncontrolled Reaction: Where neutrons will spread everywhere rapidly
https://dc.edu.au/wp-content/uploads/power-generating-fission.png
What is nuclear fusion and fission and what do they look like
Fusion: The combining of two light elements which forms a heavier element and releases energy + neutron/s
Fusion: The splitting of one heavy element by a neutron into multiple lighter elements and releases energy + neutron/s
https://img.jagranjosh.com/imported/images/E/GK/Fission-Fusion-reaction-difference.png
Which pieces of evidence showed that protons and neutrons were NOT fundamental particles?
- beta decay showed protons and neutrons can change form
- Neutrons had a magnetic moment despite not having a charge
- In 1969, high energy particle accelerators indicated tiny particles within protons and neutrons
What are protons and neutrons composed of respectively?
Up (+2/3) and down quarks (-1/3)
P = U + U + D = +1 N = U + D + D = 0
What are the four groups of particles?
Matter particles (and anti matter equivalent - Quarks - Leptons Force particles (aka gauge bosons) Higgs Boson
Name of quarks?
Up, Down, Charm, Strange, Top, Bottom
What are the two ways to categorise quarks?
3 Generations (which increase in mass left to right) 2 Charges (top row 2/3, bottom row -1/3)
Why can’t quarks exist on their own and if so, how can they exist?
Due to the massive amount of energy required to separate quarks, if it happened, new quarks would be created from this energy
They exist in combinations called hadrons
What are the two types of hadrons?
Baryons; made of 3 quarks
Mesons; made of a quark and an anti quark
What attributes must be different in order to not violate Pauli’s Exclusion Principle?
Spin
Colour (Red, Blue, Green)
note colour doesn’t refer to actual colour, it’s just a metapha
How should colours add up to adhere to the conservation of colour?
In baryon, Red + Blue + Green = White
In meson, Colour + ‘Anticolour’ = White
note anticolour is the opposite of a whatever colour
Name of leptons?
Electron, Electron neutrino, Muon, Muon neutrino, Tau, Tau neutrino
What are the two ways to categorise leptons?
3 Generations (which increase in mass left to right) 2 Charges (non-neutrino row -1, neutrino row 0)
What are the four fundamental forces and where do they act?
Gravity → Anything with mass
Electrostatic → Anything with charge
Weak Nuclear Force → In beta decay
Strong Nuclear Force → Between quarks and nucleons
What bosons (force particles) do the fundamental forces work through?
Gravity → *Graviton
Electrostatic → Photons
Weak Nuclear Force → ±W, Z Particles
Strong Nuclear Force → Gluons (between quarks), *Pions (between nucleons)
- note* gravitons are hypothetical and have not been discovered
- note* pions are not fundamental particles, but they do mediate the SNF
How do photons mediate electromagnetism?
They exist as a virtual particle and when two charged objects interact, the photons coming out of the charges will either;
- collide and repel
- exchange photons in a way where they attract
How do weakons mediate weak nuclear force?
They will emit a virtual particle, changing a proton into a neutron (vice versa) in the form of a W+, W- or Z which then splits into;
- W- = Electron + Antineutrino
- W+ = Positron + Neutrino
- Z = others (neutrally charged)
How do gluons mediate strong nuclear force?
Gluons are virtual particles which create an attraction between quarks through particle exchange
How do pions mediate strong nuclear force?
Pions are virtual particles composed of a quark-antiquark pair which create an attraction between quarks through particle exchange
What particle creates mass for the particles (most notably the weakons)?
Higgs boson, with a Higgs Field
What are the 3 major problems with the Standard Model?
- Can’t explain gravity
- Can’t explain dark matter and energy
- Can’t explain the matter-antimatter inequality
Linear Accelerator?
Ions travel through and are accelerated by multiple drift tubes which are separated by progressively greater distances, with an AC voltage in a long linear path
Cyclotron?
Particles spun around between 2 magnetic Ds until they get spun outwards and hit a target. The gap between the 2 Ds increase the speed and radius of orbit
Synchrotron?
A particle is introduced into the machine and accelerated with a constant radius by increasing the magnetic field strength, before hitting a target
Advantages of Synchrotron?
- They can travel much faster
- Have greater energy
Disadvantages of Synchrotron?
- They can only have one packet of charged particles at a time (unlike cyclotrons)
What is the purpose of a particle accelerator?
They increase the speeds of particles, giving them great energy, replicating the conditions of the Big Bang
Formula for wavelength of emitted photon
1/λ = R[1/(nf)^2 - 1/(ni)^2]
[R = 1.097 x 10^7]
Formula for wavelength of de Broglie matter waves
λ = h/mv
[h = 6.626 x 10^-34]
Formula for radioactive decay
Nt = Noe^-λt
note the decay constant (λ) depends on the chemical and is either given or you must calculate it. Time (t) is in reference to decay time
Formula for decay constant
λ = ln(2)/t(½)
note t(½) is the time it takes for a piece of matter to be halved
When an atom absorbs energy, the electron goes (shell)?
Likewise, when an atom releases energy the electron goes (shell)?
up,
down
