Physics HSC

Physics 2025

Low Earth Orbit Satellites

• orbit approx 500km

• 1 orbit approx 90 mins

• used for:

  • weather

  • military monitoring purposes

Geostationary Satellites:

• orbit every 24 hours

• around 35,000 km above

• used for

  • tv broadcasts

  • mobile phones.

Keplar’ 1st law

The orbit of every planet is an ellipse with the Sun at one of the foci.

Keplar 2nd Law

A line joining a planet and the sun sweeps out equal areas during equal intervals of time.

Keplar 3rd law

The square of the orbital period of a planet is directly proportional to the cube of the semi‐major axis of its orbit. T2  R3

Unit for magnetic flux

wb webber - Tm²

Define Emf. + measurement

• Volts

electric force from converting any form of energy into electrical energy

• when a conductor cuts magnetic field lines.

faradays law

induced emf is proportional to the rate of change of magnetic flux.

Lenz’s law building upon faradays

minus sign

• direction of induced emf

• induced current’s magnetic field opposes the original change in flux

N

• number of coils increases induced emf.

Conservation of energy + lenz’s law working

because the the magnetic field opposes the motion, work needs to be done to either the coil or the magnet.

this works is being converted into electrical energy.

If conservation of energy law is broken lenz’s law?

if magnetic field doesn’t oppose motion

• magnet moves and cuts flux lines, this attracts magnet and it moves faster.

• as it moves faster more flux cut per second, field strength increases, magnet moves perpetually faster.

• break law of conservation of energy.

4 ways transformers are inefficient

1. heating effect of current in coil

2. heating effect of induced eddy currents

3. flux leakage

4. magnetism of the iron core

How is power lost from heating of core from current in transformers + how to resolve this?

How:

• As a current flows through the coil, it heats

• lower is lost as heat I²R.

Fix:

• thick copper wires - low resistance

• use coolant to reduce the temperature of the transformer.

How is power lost from heating of core from eddy currents in transformers + how to resolve this?

How:

• when the magnetic field in the iron core fluctuates, eddy currents are generated in the iron core - heating

Fix:

• use a laminated iron core, where layers are insulated with enamel paint

• resistance reduces prevalence of eddy currents and heating.

How is power lost from flux leakage in transformers + how fix?

How:

• some of the induced magnetic flux in the primary coil is not transmitted to the secondary coil, thus emf in the secondary coil is decreased.

Fix:

• secondary coil coils tightly intertwined with the primary coil, to increase flux linkage.

• Iron core forms a closed loop.

How is power lost from magnetisation of iron core in transformers + how fix?

How:

• the energy used to magnetise and de-magnetise the iron core each time the current changes direction is known as HYSTERESIS.

Fix:

• Use a soft iron core that is more easily magnetised and de-magnetised.

DC motor parts + Roles -6

Magnets:

• supply magnetic field.

Armature:

• carries coils, has laminations to reduce eddy currents

Coils:

• provides torque, as current in coil cuts magnetic flux

Split Ring commutator:

• point of contact between rotor coils and external circut

• serves to reverse direction of current flow in each half revolution, this maintains torque.

Brushes:

• fixed electrical contacts between circuit and commutator

Axle:

• centre of rotation for moving parts of rotor.

Operation of an AC induction Motor

• as the magnetic field rotates the conductive metal rods in the rotor cut the magnetic flux, inducing an emf and current in the rotor bars

• this current induces an opposite magnetic field, lenz’s law

• newtons 3rd law (every action has an equal and opposite reaction), so the magnetic repulsion (force) between the induced B feild and rotating feild causes the rotor to rotate (anti-clockwise, same direction as field).

• the torque causing the rotor to rotate is induced and the rotor always rotates slower than the feild.

• this converts electrical energy into mechanical energy.

How Magnetic Breaking Works?

Examples of Magnetic Breaking

• trains 

• amusement Park

Energy Conservation in magnetic breaking

energy is seen to be conserved as kinetic energy is transformed into thermal energy in the conductive material.

Maxwell’s 4 equations?

1. any electric charge produces an electric field. (gauss’s law)

2. magnetic monopoles can never be found in nature (gauss’s law in magnetism)

3. a changing magnetic field induces an electric field (faraday’s law of induction)

4. a changing electric field induces a magnetic field. (ampere-maxwell law)

Maxwell’s contributions

• showed that light was an electromagnetic wave

• he theorised that electromagnetic waves:

  • can propagate through empty space

  • propagate through space at the speed of light

  • generated by oscillating electric charges.

  • carry energy and momentum

  • cover many frequencies

Hertz validating maxwell’s predictions?

• used an induction coil with a high voltage source, connected to a transmitter

• transmitter has two spherical electrodes

• a spark was seen to jump between the electrodes - energy transferred at the speed of light

• this showed the em spectrum exists by detecting em waves (radio waves).

original bar used to measure a meter

platinum iridium bar

what is black body radiation and what is a black body.

radiation emitted from a heated object

• a black body is a cavity in a material which only emits thermal radiation, incoming radiation is absorbed in this cavity

Application of black body radiation

cooler objects:

• emit less radiation

• appear reddish

hotter objects:

• emit more radiation

• appear yellowish

As a black body heats up, increases in intensity, wavelength for max intensity reduce

Examples of a black body

• lava

• sun and other stars

• heated metal

What unit is weins displacement law in and conversion

in kelvin - to convert degrees to kelvin + 273

when is diffraction optimised?

when the size of the gap is equal to the wavelength of the incident wave.

Newton’s theory of light - what is it?

Theory:

• waves are particles - called corpuscles

• corpuscles travel in straight lines in all directions at high speed

• when corpuscles enter the eye = sensation of vision.

• different sized corpuscles = different colours

• repelled by reflective surfaces, attracted by transparent surfaces.

Newtons theory of light positives + negatives

Positives:

• explains rectilinear propagation

• explains refection + refraction separately.

Negatives:

• cannot explain simultaneous reflection + refraction.

• cannot explain diffraction

• though velocity of light was faster in a denser medium.

• if particle emitted from source, mass should reduce.

Huygen’s theory of light - what is it?

because light travelling in particles would collide - proposed light as a longitudinal wave.

Wavelets:

• light spreads out evenly in all directions

• all wavefronts could be a source of spherical wavelets - with same velocity, frequency and phase.

• when wavelets are in phase they combine to create a new wavefront.

• waves propagate due to the superposition of wavelets.

Huygen’s theory positives + negatives

Positives:

• explains diffraction

• explains partial reflection + refraction

• light moves slower in a denser medium.

Negatives:

• assumed the existence of an ether

• cannot explain rectilinear propagation.

• cannot explain light bending.

• thought waves were longitudinal

Classic model vs quantum model

Classic:

• frequency - affects colour

• Intensity - amplitude

Quantum:

• frequency - energy

• intensity - number of photons

Photoelectric effect process + Results

• light shone onto a metal plate

• if light has enough energy it should knock photoelectrons off.

• in an electric field to attract disturbed photoelectrons, and in a vacuum.

Results:

• below a threshold frequency, increasing intensity did not produce photoelectrons.

• above threshold frequency Increasing intensity produced more photoelectrons

• increasing frequency of incident light, made escaping photoelectrons move faster.

• KE of emitted photons was dependant on frequency.

What is planks constant

rate at which Kmax of escaping photoelectrons is changing with respect to frequency (gradient of work function graph).

What is a work function

minimum ammount of energy required for a photoelectron to escape

What is an inertial frame of reference?

• a frame with no net external forces acting upon it

• no acceleration

• where newtons 1st law will be obeyed

What are Einstiens postulates?

1. all inertial frames of reference are equivalent.

2. the speed of light in a vacuum is an absolute constant.

what does Einstiens 1st postulate mean?

• there is no absolute frame of reference

• no experiment can be performed entirely within and intertial frame to determine whether it is resting or stationary.

Einstein’s thought experiment 1

superman flying at the speed of light can or cannot see his reflection.

• yes - light would have to exceed c

• no - he must know he is travelling at c

Einstein’s thought experiment 2

light bulb in the centre of a carriage with doors at either end with light sensors.

• person inside see at same time

• person outside see rear door open first.

What is a muon?

Subatomic particles created by interactions between cosmic rays and gas molecules in the upper atmosphere.

• travel towards earth at speeds close to c.

• have an average lifespan of 2.2 microseconds

How are Muons evidence for special relativity?

• live only 2.2μs

• newtonian physics predicts in this time they could only travel 660m but they are created multiple kilometres above earths surface, should shouldn’t ever reach the surface.

Time dialation:

• from earths perspective, the time of the muon dilates, so earth see’s them make it to the surface.

Length Contraction:

• from the muon’s perspective, the distance to the earth is shorter, length contraction, so they see themselves making it.

What is an atomic clock

• very precise clocks

• use the frequency of radiation emitted during electron transitions within atoms to measure time.

• this allows them to measure very small time differences.

Hafele keating + atomic clocks evidence for special relativity.

• three atomic clocks were used, one on earth, one on a plane travelling west, and one on a plane travelling east.

• earth rotates to the east, so relative to earth, the west travelling plane moved faster. 

• the time relative to earth on west travelling plane dilated more than the eastward plane.

Big bang before -2

• hot point of energy called a singularity

• high radiation and heat

Within the first second of the big bang - 5

• cosmic inflation

• 4 fundamental forces separate (strong, weak, electromagnetic, gravitational)

• fundamental particles called quarks are created from energy - ‘quark soup’

• quarks, leptons and neutrinos make up most of the universe’s matter

• as the universe expands, it cools, quarks collide, this forms hadrons (protons + neutrons).

3 mins after the big bang to 380,000 years after -4

• leptons and anti leptons annihilate each other leaving a surplus of matter particles, (electrons).

• primordial nucleosynthesis - temperature drops and nuclei form through nuclear fission (hydrogen, helium, lithium)

• electrons and nuclei are unattached

• universe is opaque

380,000 years after the big bang and onwards - 5

• temperature drops below 3000K, electrons start to orbit nuclei, forming the first atoms.

• universe is transparent.

• lots of photons released from recombination, cosmic background radiation.

• temperature low + gravity = first galaxies.

• heat from gravitational compression - thermonuclear reactions = first stars formed.

evidence for the big bang

Cosmic background radiation

• radio waves

• longer wavelength than visible light

• suggests universe expanding, and has expanded from a singularity - big bang.

Hubble’s constant

the further a galaxy away, the more redshifted em radiation is.

• suggests galaxies are moving away and the universe is expanding.

how to determine the temperature of a star

wiens law.

hertzsprung russell diagram

plots luminosity (or magnitude) against surface temperature.

A - blue giants

B - supergiants

C - main sequence stars

D - red giants

E - white drawfs

apparent magnitude vs absolute magnitude

apparent magnitude - how bright the star appears from earth

Absolute magnitude - how much light is actually given off.

Main sequence stars

90% of stars

younger only fuse hydrogen - pp chain

older main sequence fuse hydrogen but use PP chain and CNO cycle.

Red Giants + Red super giants

Fused most of their hydrogen

now fuse helium, becomes carbon - tripple alpha process.

White drawfs

• no more nuclear fusion

• energy from residual heat.

Life cycle of stars - small stars

1. nebula

2. protostar

3. main sequence star

4. red giant

5. planetary nebula

6. white dwarf

Life cycle of stars - large stars

1. nebula

2. protostar

3. main sequence star

4. red super giant

5. super nova

6. neutron star - or - black hole.

Proton-Proton chain summary

• fuses hydrogen into helium in two nuclear fusion reactions

• converts 4 hydrogen nuclei into a helium nucleus.

• this process is called nucleosynthesis

• as the mass of the individual hydrogen molecules is greater than the two combined - some mass must be converted into energy

• e=mc²

• energy is released in the form of gamma ray photons

Proton-Proton chain process

A hydrogen nucleus = a proton

1. 2 ¹hydrogen nuclei combine to form a ²hydrogen (deuterium) - positron and neutrino produced

2. a ¹hydrogen collides with a deuterium to form helium (tritium) - gamma radiation released.

3. two ³helium collide, to form ⁴helium - two ¹hydrogen released.

CNO Cycle

a series of nuclear fusion reactions which occur in main sequence stars - like our sun

involves carbon, nitrogen, and oxygen

a He-4 nucleus is normed fro every one cno cycle.

gamma radiation is produced.

Tripple alpha process

fuses helium to produce helium and carbon.

Cathode v anode

cathode: negative electron emitting electrode

anode: positive electron absorbing electrode

what is a cathode ray

• Cathode rays were produced in partially evacuated discharged tubes called Crookes tubes

• a cathode ray tube consists of two electrodes connected to a high potential difference. (cathode + anodes

• energy given to cathode to emit cathode ray - eg: heating - thermionic emission

• ray - streams of electrodes (scientists originally didn’t know electrons existed).

Thomson Charge to Mass ratio experiment

• developed charge to mass ratio

• found that the cathode ray was deflected in both E and B feilds.

• found when F(E) was equal and opposite to F(B) and cathode ray was undeflected.

• found electron was 1800x less than hydrogen

  • Atoms were made of smaller particles

  • Plum pudding model

Thomson deriving charge to mass ratio

• B field:

  • F_B = F_C

  • qvb = mv²/r

  • q/m = v/Br

• E field:

  • F_E = qe

  • F_E = F_B

  • qE = qvb

  • v = E/B

• Equate:

  • q/m = E/B²r

Milikans Model

Purpose: to find the charge of an electron

Process:

1. fine oil sprayed - falls due to gravity

2. x rays negatively ionise the droplets (gain electrons)

3. E field is applied - F_E on droplets

4. F_E is adjusted to be equal and opposite to to gravity - droplets are suspended

5. velocity found using kinematics

6. F_E = mg

7. charge on droplets is always a multiple of -1.602×10^-19

Chadwick’s experiment

• discovered the neutron

How:

• bombarded beryllium with alpha particles

• emitted a stream of radiation

• very penetrating - didn’t get reflected

• the stream hit paraffin and carbonised it

• the rays did not move an electroscope so was not gamma as originally thought.

• using kinematics chadwick found velocity of protons

• using momentum conservation and proton velocity - chadwick determined the mass of a neutron.

• Paraffin has a large number of hydrogen atoms containing single protons. When the unknown radiation hit these protons, they were ejected from the paraffin.

History of the atom -6

Democritus:

• solid indestructible, no electrons or hadrons

Daltons atomic theory:

• tiny particles - not subdivided, created or destroyed

JJ Thomson:

• discovered the electron, negatively charged so must have positive charges to counteract this - plum pudding model.

Ernest Rutherford:

• gold foil, alpha particles, some defelcted/bounced/passed through - discovered the nucleus:

  • small

  • large mass

  • positively charged

Bohr Model:

• planetary model

• electrons travel in definate orbits around the nucleus

  • closer orbits, more stable

  • electrons moving between orbits - emits spectra.

Quantum mechanic model/ Schrodinger’s atom model

• based on theory of wave mechanics

• atom mostly empty space

• two regions:

  • nucleus - protons+neutrons

  • electron cloud - where likely to find an electron

Limitations of Rutherford

• an electron orbiting a nucleus should be accelerated towards the nucleus

  • this should cause the electron to continuously emit radiation and loose energy.

  • thus the electron would slow, not be able to resits the nucleus’s attraction and spiral inwards.

• does not explain the arrangement of electrons in the atom.

Bohr’s postulates -4?

• electrons can orbit the nucleus in metastable orbits without radiating energy or falling towards the nucleus despite having an opposite charge.

• when an electron moves to a lower orbit it emits em radiation E=hf

• if an electron moves to a higher orbit it must gain energy e=hf

• angular momentum is a multiple of mvr=nh/2(pi)

Bohr Limitations -4

• could not explain spectra Relative Intensity.

• Could not explain spectral Hyperfine structure

• only account for Hydrogen emission spectrum (one electron in valance shell)

• cannot explain the ‘Zeeman’ splitting of spectral lines in a B field.

Balmer series

emission lines in visible light range (hydrogen)  - drops to n=2

De Broglie idea

Proposed that moving matter can exhibit wave properties

• postulated that electrons orbit the nucleus as standing waves.

When electrons behave as standing waves they no longer emit radiation - provided an explanation for bohr’s 1st postulate.

• so electrons should be able to be diffracted and have interference patterns

Davisson + Gremmer experiement + de broglie confirmed

1. fired electrons at a nickle target.

2. the slits between the nickle atoms acted as a diffraction grating to diffract electrons

3. the image of the metals crystal lattice was then able to be obtained obtained

as the electrons were diffracted - the exhibited a wave nature - this supported De Broglie’s theory

Transmutation Def

changing one element into another by radioactive decay, nuclear bombardment, or similar processes.

• alpha, beta or gamma decay.

isotopes?

same atomic number different mass number - same number of protons, different number of neutrons.

Radioactivity

spontaneous emission of radiation from an unstable nucleus

• to be radioactive must absorb radioactive elements

Types of radioactive emission

Alpha:

• Particle type:

  • helium nucleus

• Penetrating ability

  • low

• ionising ability

  • high

Beta:

• particle type:

  • electron

• penetrating ability

  • medium

• Ionising ability;

  • medium

Gamma radiation:

• Particle type:

  • gamma ray photon

• Penetrating ability:

  • high

• Ionising ability

  • low

Alpha decay

helium nuclei emitted

^A_ZX → ^{(A - 4)}_{(Z - 2)}Y + ⁴₂He

Beta Decay minus

when a neutron changes into a proton, which causes an electron and antineutrino to be released.

^A_ZX → ^A_{(Z + 1)}Y + ⁰_-1 e + V(anti)

Beta Decay plus

proton changes to a neutron, and a positron and a neutrino are released

^A_ZX → ^A_{(Z - 1)}Y + ⁰₊₁ e + V

Gamma Decay

when a gamma ray photon is emitted, and the nuclear energy level decreases.

typically occurs alongside other decay types

^A_ZX → ^A_Z Y + ⁰₀γ

Half Life summary info

nuclei decaying is randomly occurring, and it cannot be predicted when a nuclei will decay.

through examining large number of nuclei, the probability that a nuclei will decay in a given time period can be determined.

half life = time for half the nuclei to decay.

(decay curve will never reach zero).

short v long half life

short = more radioactive isotope.

long = less radioactive isotope.

Fission Def?

a large nucleus is bombarded by a neutron, and it splits into 2 smaller nuclei and neutrons.

• products of fission have a smaller mass so energy produced - E=mc²

Fission Process?

1. neutron collides with a nucleus (typically uranium-235)

2. nucleus captures the neutron, which causes instability in the nucleus (uranium-236 is very unstable).

3. the nucleus splits into two fission fragments and releases neutrons

Uncontrolled fission reactions

a chain reaction when the fission of a nucleus produces neutrons which bombard another nucleus - chain reaction - multiple fissions

Real life fission examples

Controlled:

• nuclear power - uranium-235

Uncontrolled:

• Nuclear Bombs

  • Little boy - hiroshima

  • Fat man - nagasaki

Controlled fission reactions - power plant components to control

Fuel rods:

• contain nuclear fuel (uranium 235),

• surrounded by a moderator (eg: water) which controls the number of neutrons released.

• slower release of neutrons - less nuclear reactions per second.

Control Rods:

• control the rate of fission by moving in and out (absorb neutrons). (eg boron)

  • in = rate decreases

  • out rate increases

  • all in = stops

How nuclear power plants produce energy?

• energy released heats up the reactor

• water surrounding the reactor is heated, boiled to produce steam

• steam drives the turbine which turns a generator - producing electricity.

Nuclear Fusion?

two nuclei with low mass numbers to produce a single nucleus with higher mass numbers.

Fusion Process

2 nuclei collide

energy (em radiation) is released + typically a nucleon also.

Binding energy

• the energy binding nucleons together (per nucleon)

• measure of nuclear stability - high binding energy = more stable atom.

Binding energy Fe56

most stable element - more protons = more likely to undergo fission - less protons = more likely to undergo fusion.

• threshold

a reaction occurs when the products are more stable than the reactants.

Standard model what in

• fundamental forces

  • strong

    • boson = gluon

  • em

    • boson = photon

  • weak

    • boson = w + z particle

  • gravitational

    • boson = graviton

• Quarks:

  • up

  • down

  • strange

  • charm

  • bottom

  • top

• Hadrons:

  • Baryons

    • protons + neutrons

  • Meysons

    • pions

• Leptons

  • electron + muon

The Fundamental Forces:

EM force:

• binds charges particles atoms + nucleus

  • infinite range

  • boson = photon

EM force:

• binds charges particles atoms + nucleus

  • infinite range

  • boson = photon

Weak Nuclear force:

• binds interacts with nuclear particles

  • limited range

  • boson = w and z particle

Gravitational Force:

• draws masses together