M8 From The Universe To The Atom Flashcards
basic evolution of the universe
what happened after the big bang
Inflation
an extremely short period during which the universe expanded out from a single point
shortly after the BB, what happened in terms of mass
the universe did not have an increase in mass
as the universe rapidly expanded outward and occupying more space, the density of the universe decreased causing the universe to rapidly cool
some time after BB, matter was formed from
matter was formed from energy
(not hydrogen and helium atoms, antimatter or a continual process of annihilation)
what is annihilation
the transformation of matter to energy, it occurs when antimatter and matter pairs collide
when they collide, their mass returns to energy
how were stars initially formed
basic matter clumping together in free space
hundreds of millions of years after BB, the universe was relatively calm. once enough mass accrued into a single clump, its own sheer size initiated fusion inside of it, forming a star
what happens when stars die
stars under fusion inside their cores
fusion combines smaller elements into larger more complex ( heavy elements) ones to produce energy. when stars die, all the heavy elements formed inside their core are released into the universe
what is an AU
what is a solar mass
what does hubble’s law tell us
used to find out how fast a galaxy is moving away from us, given its distance away
hubble’s law graph
hubble’s law spectra
red shift - interpreted to mean that galaxies are receding away from us at very high velocities
what is a black body radiator
absorbs all incident EM radiation and will emit different amounts of each frequency of light
for a particular temperature, there is a unique spectrum emitted
what happens to spectral radiance as the wavelength of light emitted approaches zero
spectral radiance (intensity) approaches zero regardless of the temp of the body
there is no such thing as light with wavelength of zero
why are black bodies called that
from the fact that they absorb all colours of light
black bodies come in huge ranges of colours
a gas discharge produces a discrete spectrum of light
an incandescent lamp produces a continuous spectrum of light
identify an assumption of each model which determines the shape of its curve
classing stars TEMP
stars at a higher temp will emit radiation at a higher frequency and be bluer
classing stars LUMIOSITY
intrinsic brightness of a star is how much energy it gives off
brightness doesn’t take into account the distance
spectral class
highest temp to lowest classes
colour
OBAFGKM
temp range of stars
2000K - 50 000K
hertzsprung russell diagram
x axis
y axis
3 main groups
life of a star starting on main sequence
main sequence
red giant
yellow giant
red supergiant
planetary nebula
white dwarf
where are the hot/cold/bright/dim stars
most stars begin their lives and live most of their days on the main sequence
our sun on HR diagram
HR diagram giants
how bright? how hot?
stars migrate off the main sequence and reach later stages of life as giant
HR diagram white dwarves
how bright? how hot?
have very long lifetimes
HR diagram how to figure out mass
as mas increases, so does luminosity
if a star has more mass, its core is under a greater amount of pressure and fusion occurs more frequently
more fusion means more energy, which is more luminous star
y axis on HR diagram
shows luminosity RELATIVE to our Sun
how much energy a star outputs in each stage of their life
x axis on HR diagram
temperature in Kelvin
relate temp to its colour, spectral class and what kind of fusion within its core
white dwarves
extremely hot (as residual heat from previous stage) , however do not undergo any fusion, so they don’t produce any energy so they’re not luminous
as white dwarves age, where do they move on HR diagram
they are always cooling as they age
as their temp drops, they will move slowly to the right of HR diagram
age of the 3 main groups on HR diagram
main sequence
then they transition to red giants because they run out of hydrogen fuel for fusion
then becomes white dwarf once fusion stops entirely because ALL of its fuel has run out
initial formation of stars
protostar (hydrogen gas and stellar dust) held together by gravity
begin to collapse in on itself
pressure increases, generating heat
hot enough to ignite hydrogen and start nuclear fusion
protostar def
protostar: a cloud of hydrogen gas and stellar dust in space held together by gravity
the more massive the main sequence star on HR diagram
main sequence stars are characterised by…
nuclear fusion of hydrogen into helium (2 H into 1 He)
helium has less mass than hydrogen
(this mass defect is converted into energy)
this energy provides pressure outwards that balances inward force of gravity, which stabilises the star
hydrogen fusion 2 varieties
proton-proton chain
or
CNO cycle
proton-proton chain
form of hydrogen fusion
main process for small main sequence stars
4H→He-4
cno cycle
form of hydrogen fusion
main process for big main sequence stars
converts a carbon (catalyst) atom between nitrogen and oxygen to produce
4 hydrogen nuclei –> 1 helium nucleus & energy
after hydrogen fusion
when the star runs out of hydrogen fuel, the core starts to contract and outer gas shell expands
temp drops and luminosity increases as star becomes RED GIANT
how are giant stars formed
when hydrogen fuel runs out and helium is used as fuel instead
helium fusion requirement and effect on star
requires much higher temp to initiate fusion
star overall temp is decreasing but the core temp is increasing
2 processes of helium fusion
triple alpha process to carbon
helium fusion into oxygen
< 8 solar masses (He fusion)
stop fusion after He runs out and leave core filled with carbon and oxygen
> 8 solar masses (He fusion)
continue fusion and leave core filled with iron
how is fusion inside stars initiated
by gravitational force
the squeeze from gravity generates heat and pressure in the core
a star would collapse under its own gravity if not for…
the outward pressure from fusion in the star’s core
what are protostars formed from
basic elements in free space
why is CNO cycle H fusion for larger main sequence stars
fusion processes involving heavier elements require more energy to initiate
proton-proton chain involves light elements however since carbon and oxygen are heavier (needs more energy) , fusion can occur
how much energy is released during the proton-proton chain fusion of H to He
describe two processes which account of energy production in stars
(death) white dwarves are formed when
helium runs out and star loses mass (main sequence to giant to white dwarf)
< 8 solar masses (smaller main sequence stars)
( death) neutron stars
red giants (from larger main sequence stars) are fueled by He fusion then core is filled with iron
when He runs out, star explodes
supernova (explosion that compresses the star’s core)
neutron star
small and dense core
8-20 solar masses
( death) black holes
red giants (largest main sequence stars) are fueled by He fusion which fills core with iron
when He runs out, star explodes
supernova (explosion) due its size, the remnants collapse and form black hole
black hole is infinitely small and dense, prevents light from escaping
death of stars
MS is main sequence
small MS < 8 solar masses
red giant (He into C, O)
white dwarf
medium MS 8-20 solar masses
red giant (He into C, O, Fe)
neutron star (medium supernova)
big MS > 20 solar masses
red giant (He into C, O, Fe)
black hole (big supernova)
death of star HR diagram
why do stars die
they run out of fuel
outward fusion forces are required to balance the inward force of gravity on the star
when fuel runs out, no more fusion, star collapses
the effects of gravity play a significant role in stellar evolution. describe the processes of death for stars with masses above and below 8 solar masses and the role gravity plays
what is an arcsecond
what is a parsec
what is parallax (angle)
the apparent change in position of an object when you observe it from 2 different points
more distant galaxies are receding from Earth at
greater rates, proportional to their distance from Earth
Hubble’s constant
The Hubble constant (denoted H₀) is a measure of the rate at which the universe is expanding
units: kilometers per second per megaparsec (km/s/Mpc)
relative mass and charge of protons, neutrons and electrons
5 in ten-thousandths column
what is an isotope
a variant of a chemical element
same no. of protons (which DEFINES the element)
diff no. of neutrons
so different atomic mass, but same atomic number
element notation
(bigger number)
atomic mass (nucleon number = protons + neutrons)
atomic number (protons)
def of amu (atomic mass unit)
1/12 of the mass of carbon-12 isotope
(roughly the mass of a single nucleon)
cathode ray def
beam of electrons
electron beam
cathode ray tube composition
made of glass
evacuated (vacuum inside to minimise cathode ray collisions with air etc)
cathode ray tube “process”
the cathode is heated
thermionic emission (giving off charged particles with heating)
the free electrons within a heated metal gain a lot of KE
with sufficient energy, the electrons break free from the surface of the cathode
strong electric field
electrons are accelerate toward anode and some hit the glass, causing fluorescence
nature of cathode rays
experimental observation –> inference
EO: cause a sharp edged shadow when fired at a cross
I: rays travel in straight lines and can’t pass through solid objects
nature of cathode rays
experimental observation –> inference
EO: cause a glass wheel to spin along its tracks
I: rays have momentum to transfer and therefore mass
nature of cathode rays
experimental observation –> inference
fluorescence
EO: collide with glass, causing fluorescence
I: cathode rays have energy
nature of cathode rays
experimental observation –> inference
cathode to anode
EO: emitted from negatively charged cathode, attracted to positive anode
I: cathode rays are negatively charged
nature of cathode rays
experimental observation –> inference
variety of metals
EO: emitted from cathodes made from a variety of metals
I: particles comprising cathode rays are contained with every atom (the ELECTRON)
what did thomson do
charge to mass experiments
maths of charge to mass ratio
equate centripetal force and magnetic force (on electron)
thomson’s experiment
undeflected path
balance the electric and magnetic fields so the electrons have an undeflected path
equate Fb and Fe so you have an equation for v
thomson’s experiment
deflected path
turn off E field
measure deflection
equate Fc and Fb
sub v = E/B into q:m ratio equation
thomson’s experiment
turn off the E field to measure r
the radius of the magnetic field deflection
describe how milikan and thomas each used fields to determine properties of the electron
q:m value
Stoke’s Law formula
what did milikan do
measure the charge of a single electron
oil drop experiment
milikan’s experiment set up
atomiser
variable power source
microscope
opposite parallel plates
milikan’s calculations
without E field
at terminal velocity, a = 0 (no net force acts on the oil drop)
equate weight force and viscous drag force
formula for r²
milikan’s calculations
with E field
when v=0
equate electric force and weight force
formula for “q” that involves r³
significance of milikan’s results
quantised charge: charge only exists in multiples of e charge
breakthrough of idea of quantised charge (packets of particular size)
milikan’s experiment method
milikan sprayed oil drops through an atomiser and balanced the forces on the oil drop in 2 ways
1: (viscosity of air) balance weight force and viscous drag force
2: (turn on E field) balance weight force and electric force
milikan’s experiment
where did the oil drops gain their charge
from the atomiser
when the oil drops pass through the small gap in the atomiser they are charged by friction, since they are rubbing against the wall of the atomiser before they are released
did the oil drops have velocity with no E field
the oil drops were moving at terminal velocity
why need terminal velocity to measure radius of oil drop
equate mg = 6πηrv (v is terminal velocity)
mass: volume x density
radius: solve for r or r²
how did milikan measure the velocity of the drops when the electric field was turned off
since v = d/t
measured the distance and time
milikan’s experiment
why was the viscous force 0 when the E field was turned on
since the Fe and Fg balanced, the velocity was zero
oil was suspended in air
he adjusted the variable power supply to ensure Fg was balanced by Fe
how did milikan find the charge of an electron
calculating the difference in charge between a number of oil drops
when placed in E and B fields, DEFLECTION of the cathode rays occurred –> they were charged (not a property of EM waves)
cathode ray made a glass wheel spin –> they had momentum and mass
what is geiger-marsden experiment (GM experiment)
outline and hypothesis
outline: firing alpha particles at thin sheet of metal foil
(hypothesis: would support Thomson’s atom model [plum pudding is a ball of positive charge, and the plums inside it are the electrons) since the alpha particles are smaller than the atom, would not collide with anything as there was not much solid mass in the atom
what is geiger-marsden experiment (GM experiment)
results and implications
rutherford scattering
- many particles passed right through the foil
- those that scattered did so in various directions
implications:
- the atom must be a lot of empty space
- must have some very small and dense thing inside (nucleus)
- (this thing) nuclei should be positively charged (proton and neutron) [large repulsive force between the nucleus and pos alpha particles, accounting for the large deflections)
what is rutherford scattering
Rutherford scattering occurs when the alpha particles are scattered at a variety of angles by an atom (could not be explained by plum pudding)
rutherford model of atom
what is not part of rutherford’s model of atom
composition of the nucleus
protons and neutrons weren’t discovered yet
rutherford simply stated that the centre of an atom was a dense positive mass called nucleus
discovery of neutrons experiments and chadwick
the experiments
Bothe and Becker
fired alpha particles at beryllium and noticed a neutral radiation (no charge) that passed through
it was highly penetrative so they thought it was gamma rays
BUT this radiation have energy 10MeV (much more than gamma rays)
Joliot and Curie
fired the neutral radiation from beryllium through paraffin wax and noticed protons were emitted, that had energy 5MeV
discovery of neutrons experiments and chadwick
james chadwick
showed the existence of neutral, heavy particles called neutrons
mass similar to a proton
atomic model of nucleus changed from just protons to protons and neutrons
chadwick used conservation of momentum and applied it to alpha, unknown particle, and protons to draw conclusions about the mass of unknown
chadwick measured the final velocity of the protons after collision, and assuming the collisions were elastic, using conservation of momentum and KE to calculate mass of mystery
the fact it had mass showed it was a particle and not radiation
what chadwick analysed diagrams
planck’s contribution to Bohr Model
Bohr Model of Atom
(upgrade of rutherford model)
3 postulates
- Electrons exist in stable orbits around the nucleus at discrete radii, with specific energies for each orbit
- Electrons emit/absorb energy as EM radiation when moving between orbits, with the energy equal to the difference between the orbital energies
- the electron’s angular momentum is quantised
Bohr Model of Atom
3 postulates
1st
each orbit has a specific energy
these orbits are stable (electrons won’t lose energy)
energy decreases according to an inverse square law as the level increases
Bohr Model of Atom
3 postulates
2nd
electrons can move between orbits, which releases/absorbs energy (explains line spectra)
Bohr Model of Atom
3 postulates
3rd
n: orbital level
h: Planck’s constant
when jumping to higher energy level, electrons…
absorb photons
excitation
when falling down an energy level, electrons…
emit photon
de-excitation
2 limitations of rutherford model
- “orbital” decay since it loses energy when the electron accelerates
- cannot account for emission spectra
5 limitations of bohr model
1st
model cannot predict the spectra of atoms other than hydrogen
5 limitations of bohr model
2nd
model cannot explain why some spectral lines have a higher intensity than others
5 limitations of bohr model
3rd
5 limitations of bohr model
4th
5 limitations of bohr model
5th
electron energy levels
every atom has diff levels
why are the energies negative
the PHOTON’s energy is equal to the diff between energy levels
formula
E=hf is in JOULES
emission spectrum
when electrons fall down an energy level, they emit photon/s
the wavelengths of these photons are the coloured lines against the black
absorption spectrum
when you shine white light on an atom, the atom absorbs some of the light’s energy (photons)
the spectrum appears to be continuous with a set of black lines, corresponding to the wavelengths of light that are absorbed by the atoms in the gaseous substance. the photons matching these wavelengths will have an energy that is precisely equal to the amount of energy required for an electron to transition to a higher level.
MOST OF THE ABSORPTION SPECTRUM CAN BE SEEN AS A CONTINUUM OF ALL WAVELENGTHS OF LIGHT. MOST WAVELENGTHS OF LIGHT WILL NOT BE ABSORBED BY THE ATOM, SINCE THE ENERGY OF THE PHOTNS WILL NOT EXACTLY MATCH THE ENERGY REQUIRED TO JUMP LEVELS
there is no transition from the ground state with an energy difference of 5eV, so electron remains in ground state
balmer series qualitative
(ONLY HYDROGEN)
a set of specific wavelengths of light emitted by HYDROGEN atoms when an electron falls from the 3rd, 4th, 5th and 6th to the 2nd level
red, light blue, dark blue, purple
balmer series quantitative
(ONLY HYDROGEN)
energy levels in eV
balmer series quantitative
(ONLY HYDROGEN)
energy levels in J
balmer series quantitative
(ONLY HYDROGEN)
from 3, 4, 5, 6
to 2
wavelengths
red: 656nm
light blue: 486nm
dark blue: 434nm
purple: 410nm
balmer series formula
wavelength of emitted light
describe the behaviour of electrons in the Bohr model of the atom with reference to the law of conservation of energy
energy conservation is not violated as the energy absorbed or emitted is equal to the difference between the discrete energy levels of the electron
when they ask about if an atom can absorb photons with X energy, be careful
about which energy level the atom is in
so maybe it could jump from 2 to 3
but it’s in ground state so it can’t
evidence for matter as waves
Davisson and Germer fired electrons at a nickel crystal and observed how the electrons were scattered
graphing angle of deflection (scattering angle) against intensity looks like an interference pattern (diffraction)
observed electrons scattered in an alternating pattern of maxima and minima around the electron detector
electron’s interference pattern provided conclusive evidence that electrons diffract
technicalities of matter waves
De Broglie’s formula
relates the wave nature of a particle (like an electron) to its momentum. It states that every particle can be associated with a wavelength.
De Broglie’s formula tells us that any moving particle, like an electron, has a wavelength (called the de Broglie wavelength) based on its momentum
de Broglie’s hypothesis
wave-particle duality, which suggests that matter exhibits both particle and wave behaviour
what evidence do we have that light behaves like a particle and matter behaves like a wave? explain how this evidence supports the theory of wave-particle duality
particle equations…
show
must
radioactive decay
“maintain” conservation of mass and charge
3 types of radiation (not EM)
what is an alpha particle
a helium nucleus
what is a beta particle
electron
3 radiations
penetrate
ionising ability
range
penetrate
alpha: stopped by sheet of paper
beta: sheet of metal
gamma: few cm of lead
way to remember
A: not very penetrating
B: kinda
G: very penetrating
penetration vs ionising ability
what is ionising ability
ability to strip electrons from an atom
what happens when there are too many nucleons?
radioactive decay
the nucleus is too big
- the forced between the nucleons isn’t strong enough to hold it together
- nucleus becomes unstable
ALPHA PARTICLE DECAY
the atom emits 2 protons and 2 neutrons
what happens when there are too many neutrons?
radioactive decay
number of neutrons is too many?
- small atoms: more than no of protons
- large atoms: 1.5 times no of protons
BETA PARTICLE DECAY
neutron splits into proton and electron (beta particle), the proton stays, the electron is emitted as beta decay
what happens when there are too many protons?
radioactive decay
nucleus starts to decay
- protons repel each other
- this repulsive force becomes strong enough to break up the nucleus
BETA PLUS DECAY
the proton splits into a neutron and positron (anti-electron/beta+ particle), the neutron stays, the positron is emitted as beta+ decay
the neutrino
neutrino appears in beta+ decay
antineutrino appears in beta- decay
In beta decay, the total energy before and after the decay didn’t seem to match, suggesting that something was missing.
what is n vs z graph
x axis: no of protons (z)
y axis: no of neutrons (n)
key features of n vs z graph
stability line
key features of n vs z graph
unstable zones
isotopes of any size can be stable
t or f
false
any isotope with an atomic number than lead (82) won’t be stable
apparently isotopes are most stable when the N:Z is 1.5:1
standard model of matter
hadron: combo of quarks
baryon: 3 quarks
meson: quark and anti quark
proton: baryon uud
neutron: baryon udd
