G485 STANDARD ANSWERS

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G485 Standard Answer Document

Fields, EM Induction and Capacitors

Explain in terms of movement of electrons how the capacitor plates acquire an equal but opposite charge

• Electrons move from one plate to the other plate (clockwise or anticlockwise), making the

plate they leave positively charged and the plate that they arrive at negatively charged;

• The size of the charge is the same because the number of electrons that are removed

from one plate is the same as the number of electrons that are deposited on the other

plate.

Explain in terms of movement of electrons how the potential difference across the capacitor changes

• Electrons move in anticlockwise (or clockwise)

• Charge on plate decreases

• Potential difference decreases exponentially

Name the rule that may be used to determine the direction of the force acting on charge particles in a

magnetic field

• Fleming's Left Hand Rule

Explain why the speed of charged particles travelling in a uniform magnetic field does not change despite

the force acting on the charged particles

• The magnetic force acts perpendicular / at a right angle to the velocity,

• so no work is done by the magnetic force on the charged particles;

• So their kinetic energy does not change, and so their speed does not change.

Explain why an ion with a larger mass describes an arc of greater radius in a mass spectrometer

• The magnetic force (BQv) is equal to the resultant centripetal force (mv2/r), hence

BQv = mv2/r;

• Rearranging gives r = mv/BQ, so radius is directly proportional to mass.

The primary coil of a transformer is connected to an alternating voltage supply. Explain how an E.m.f. is

induced in the secondary coil

• A changing magnetic flux is produced in the primary coil;

• the iron core of the transformer links this magnetic flux to the secondary coil;

• The changing magnetic flux through the secondary coil induces an E.m.f. in the secondary

coil.

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State how you could change the transformer to increase the maximum e.m.f. induced in the secondary

coil

• Increase the number of turns on the secondary coil;

• Decrease the number of turns on the primary coil.

An AC supply is replaced by a battery (Transformer) explain why the p.d. is zero sometime after battery is

connected

• The rate of change of flux falls to zero

Describe in terms of energy conservation explain the polarity of a coil as a north pole is moved towards it

and a current is induced

• There is a repulsive force between the magnet and the coil and the work done against this

repulsive force is transferred into electrical energy in the coil

Atomic Theory and Fundamental Particles

Describe how the alpha-particle scattering experiments provide evidence for the existence, charge and

size of the nucleus

• Most of the alpha particles aimed at the gold foil went straight through, and some were

deviated through small angles;

• hence, most of the atom is empty space;

• A very small number of alpha particles were scattered through large angles (more

Than 90o);

• this showed the existence of a tiny positive nucleus;

• The size of the nucleus is about 10-14 m.

Explain why during the closest approach of an alpha particles (during alpha scattering off a gold nucleus)

the gold nucleus has a velocity and the alpha particle does not

• There is a repulsive electrical force between the gold nucleus and the alpha particles;

• linear momentum is conserved because there are no external forces;

• The initial kinetic energy of the alpha particle is transformed into electrical potential

energy.

State properties common to all isotopes of an element

• Same number of protons; same number of electrons.

• Same charge.

Name the fundamental forces experienced by hadrons (neutrons and protons)

• Strong nuclear force;

• Gravitational force.

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Particles: Study

State quantities conserved in a beta decay

• Charge;

• Momentum;

• Lepton number;

• Baryon number.

Describe the structure of the proton in terms of the quark model

• The proton is composed of two up quarks and one down quark.

Describe what happens in a beta-plus decay using the quark model

• An up quark transforms into a down quark, plus a positron and a neutrino.

Name the fundamental forces experienced by hadrons (neutrons and protons)

• strong nuclear force;

• Gravitational force.

Describe the nature and range of the three forces acting on protons and neutrons in the nucleus

Gravitational Force

• This force is attractive;

• And is long-ranged.

Strong Nuclear Force

• This force is attractive at larger distances and repulsive at short distances;

• And is short-ranged (of the order of 10-14 m).

Electrostatic Force

• This force is repulsive between protons and zero between neutrons and protons/neutrons;

• And is long-ranged.

Why is the probability of a proton and helium fusing less than two protons fusing at a given temperature

• Helium nucleus has a greater charge than a proton

• Electrostatic repulsive force between nuclei is greater hence a smaller chance of fusion

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Radioactivity

Describe what determines whether a radioisotope will decay by beta+ or beta- decay

• A radioisotope will decay by β- decay when there are more protons than required

• A radioisotope will decay by β+ decay when there are more neutrons than required

Describe what is meant by the spontaneous nature of radioactive decay of unstable nuclei

• The decay cannot be induced; it occurs without external influence.

Describe what is meant by the random nature of radioactive decay of unstable nuclei

• It is impossible to predict when a nucleus will decay.

Name the force responsible for beta decay

• The weak nuclear force.

Explain what is meant by the half-life of a..........................

• The average time taken for half of the................. In a sample to decay.

Describe carbon-dating

• Living organisms (such as plants) take in carbon (such as CO2) whilst they are alive, and

when they die, they stop taking in carbon;

• Some of this carbon will be carbon-14;

• The ratio of carbon-14 to carbon-12 for the dead object is determined;

• The current (today's) ratio of carbon-14 to carbon-12 is determined;

• The age of the sample is found using A = Ao e-λt.

Explain the major limitations of carbon-dating

• The ratio of carbon-14 to carbon-12 is assumed to be constant;

• The activity of the sample may be comparable to the background activity.

Suggest why the activity of a sample undergoing carbon-dating is measured over a long time period and

then averaged

• The activity is very small, so a long time is needed to build up enough data.

Explain why the method of carbon-dating is not appropriate for samples that are greater than 105 years

old

• The activity of a very old sample is so low that it cannot be differentiated from the

background.

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Explain why the activity of a radioactive material is a major factor when considering the safety

precautions in the disposal of nuclear waste

• If material has a large λ initial activity is high it will be highly ionising so precautions need

to be taken for the initial period of disposal

• Mater with a small λ will remain active for a long time so there is a need for long term

disposal

Describe how smoke Detectors work

• An Alpha emitter, Americium-241 is placed in a small chamber

• The alpha emitted ionizes the air so that it conducts a small current (pA is needed)

• If smoke particles enter the chamber they attract the ions and reduce the current

• The rapid drop is detected by the circuit and triggers an alarm

• The half-life of americium-241 is very long (432 years) so its natural drop in activity does

not cause a false alarm to be triggered.

Nuclear Fission and Fusion Advantages of producing electrical power by nuclear fission

• Does not produce acid rain or waste gasses that could cause pollution

Disadvantages of producing electrical power by nuclear fission

• Problems with reaction getting out of control

• Maintaining the reaction so that it proceeds continuously

• Risks from radiation: emissions due to an accident; emissions from radioactive wastes

• Long half-life of some of the waste products

Explain the term binding energy of a nucleus

• Minimum energy to separate all protons and neutrons of a nucleus.

Explain why the total mass of the individual nucleons of a particular nucleus is different from the mass of

the nucleus

• The mass of the nucleus is less than the total mass of the individual nucleons;

• The nucleus has a binding energy, so energy must be supplied in order to free the

nucleons from the nucleus;

• The binding energy is equal to the mass difference (mass defect) x c2.

Explain how nuclear fission can provide energy

• In a fission reaction, there is a decrease in the mass;

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• This mass defect is converted into energy by E = mc2.

Explain why nuclei with less than approximately 56 nucleons cannot produce energy by fission

• The binding energy per nucleon will decrease for fission, which is impossible unless

external energy is supplied.

Describe the process of induced nuclear fission

• A thermal neutron is absorbed by a massive nucleus;

• The massive nucleus splits into two daughter nuclei and one or more fast moving

neutrons.

• Coulomb repulsion pushes the fragments apart

Name two forms of energy produced in thermonuclear reactions

• Kinetic energy;

• Electromagnetic energy / photons.

Describe how a nuclear reaction can lead to a chain reaction

• The neutrons that are produced during one reaction go on to interact with other fissile

nuclei (often uranium), causing these nuclei to undergo fission reactions.

How can two protons remain together after fusion

• Attractive strong nuclear force

Describe the process of induced nuclear fission in core of sun

• Protons join together to form He Nuclei

• The protons repel one another so they need a high energy to fuse

• During the process there is a decrease in mass from total mass of reactants to total mass

of products. This mass defect is released as energy E=mc2

How Nuclear Reactors work

Explain the role of fuel rods in a nuclear reactor

• These contain the fissile material (often uranium nuclei).

Explain the purpose of using a moderator in the core of a nuclear reactor

• Fission reactions produce fast moving neutrons;

• the neutrons make collisions with the moderator nuclei and transfer some of their kinetic

energy;

• so the moderator slows down the fast moving neutrons;

• And slow moving (thermal) neutrons have a greater probability of causing fission.

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Suggest a suitable material which could be used as a moderator in a fission reactor

• Water;

• Graphite / Carbon.

Explain the purpose of using control rods in the core of a nuclear reactor

• The control rods absorb some of the neutrons;

• The control rods are inserted into the reactor so as to allow on average one neutron from

a previous fission reaction to cause subsequent fission reactions.

Suggest a suitable material which could be used in a control rod in a fission reactor

• Boron;

• Cadmium.

Discuss the physical properties of nuclear waste that makes it dangerous

• Nuclear waste is radioactive for a long time;

• And it causes ionisation, which is harmful to life.

• If λ is large short half-life so have high initial activity so precautions needed for initial

period material long half-life will last for a long time so need for long term disposal

Explain what is meant by fusion

• Fusion is the joining together of lighter nuclei in order to make heavier nuclei;

• This process releases energy as the total mass before the reaction is larger than the total

mass after the reaction.

Explain why nuclei with more than approximately 56 nucleons cannot produce energy by fusion

• The binding energy per nucleon will decrease for fusion, which is impossible unless

external energy is supplied.

Suggest a reason why fusion typically occurs at lower temperatures than those calculated in the previous

question / at temperatures as low as 107 K

• Some nuclei will have a kinetic energy greater than the mean kinetic energy and so will be

travelling faster;

• So they will have a larger energy to overcome the electrostatic repulsion, and hence

become close enough for the strong nuclear force to have an effect and cause fusion.

Explain why a proton must have a very high velocity in order to fuse together with another proton

• As the proton travels towards the other proton, it experiences an electrostatic repulsive

force that slows it down;

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• The proton needs a very high velocity to get close enough to the second proton for the

attractive short range strong nuclear force to have an effect and fuse the two protons

together.

Medical Physics: General

Explain what is meant by a non-invasive technique

• No cutting or incision of the patient's body, so no surgery is required.

State some of the advantages of using non-invasive techniques

• Lower risk of infection;

• Less trauma, such as bruising or bleeding.

Medical Physics: X-rays

State the main properties of X-ray photons

• They can travel in a vacuum;

• They travel at the speed of light in a vacuum;

• They have no charge;

• They have no rest mass;

• They are highly ionising.

Explain why an X-ray photon has greater energy than a photon of visible light

• E = hf;

• X-ray photons have a higher frequency than visible light photons, so they have a higher

energy.

Describe briefly how X-rays are produced in an X-ray tube

• Fast moving electrons hit a metal surface;

• The loss in kinetic energy of the electrons produces X-ray photons.

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Describe how X-ray photons are produced in a hospital X-ray machine

• Electrons are accelerated through a high potential difference;

• the high speed electrons hit a metal surface;

• The loss in kinetic energy of the electrons produces X-ray photons.

Describe the Compton Effect in terms of an X-ray photon

• An X-ray photon interacts with an orbital electron;

• The electron is ejected and the energy of the scattered photon is reduced.

State interaction mechanisms between X-ray photons and matter, and describe what happens during the

mechanism to the X-ray photon interacting with a single atom •

Photoelectric effect; the X-ray photon provides enough energy to remove a

delocalised/free electron from the surface of a metal, and provides kinetic energy to

the electron;

Compton scattering; the incoming X-ray photon collides with an electron in an atom. The

electron is ejected from the atom and the photon is scattered with a lower energy;

Pair production; the incoming X-ray photon disappears and produces an electron positron

pair.

Name an element used as a contrast material in X-ray imaging

• Barium or iodine

Explain why contrast materials are used in the diagnosis of stomach problems

• The contrast medium absorbs X-rays because it has a large attenuation coefficient (it has

a larger atomic number);

• This is ideal for imaging the outline of soft tissues, as if there is a hole then the barium will

highlight this by flowing out of the hole, revealing problems with the tissue.

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Describe the use of image ores when X-rays are used to produce images of internal body structures

• Intensifier is used as X-rays would pass through the film;

• Intensifiers converts an X-ray photon in to many visible light photons, which are absorbed

by the film;

• Therefore, a lower exposure to X-ray radiation is needed.

Explain how image intensifiers are used to improve the quality of the X-Ray Image

• Absorption of X-Rays by (silver halide molecules) a photographic film releases many

photons

• Use of Fluorescent/scintillator/phosphor

• Photons release electron that are accelerated onto fluorescent screen

• Number of electrons increased

Describe the operation of a computerised axial tomography (CAT) scanner

• An X-ray beam passes through the patient at different angles as the X-ray tube rotates

around the patient;

• A thin fan-shaped beam is used;

• Images of slices through the patient in one plane are produced, with the help of computer

software;

• X-ray tube / detectors are moved along the patient for the next image slice through the

patient.

State an advantage of a CAT scan image over a conventional X-ray image

• 3D image;

• Better contrast between different (soft) tissues.

• Image can be rotated

Explain how the production of a CAT scan image differs from that of a X-ray image

• A simple X-ray produces a single image;

• Whereas a CAT scan takes images at many different angles.

• Computer processes data/image constructed from many different slices

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Medical Physics: Ultrasound

State the main properties of ultrasound

• Longitudinal wave;

• Frequency of sound is greater than 20 kHz.

Describe the piezoelectric effect

• The application of a potential difference across a crystal causes a vibration of the crystal

atoms.

Describe how the piezoelectric effect is used in an ultrasound transducer both to emit and receive

ultrasound

• Emission: the piezoelectric film / crystal is connected to an alternating potential difference,

making it vibrate / resonant, and hence emit ultrasound;

• Reception: ultrasound makes the piezoelectric film / crystal vibrate / resonant and this

produces an alternating potential difference.

Describe the principles of ultrasound scanning

• A piezoelectric transducer is used to send pulses of ultrasound into the patient;

• The ultrasound signal is reflected at the boundaries between tissues;

• The intensity of the reflected signal depends on the acoustic impedances at the boundary,

which is linked to the type of tissue;

• The time between transmission of the waves and receiving the reflected wave is used to

determine the depth of the tissue boundary.

What is meant by acoustic impedance matching

• The acoustic impedances of the media are similar.

Explain why a gel is used between the ultrasound transducer and the patient's skin during a scan

• Without the gel, the ultrasound would be reflected at the skin to air interface, so the gel

allows the transmission of the ultrasound into the body;

• The gel and the skin have similar acoustic impedances.

Explain the difference between an ultrasound A-scan and B-scan

• An A-scan is one directional, whereas a B-scan involves different directions / angles;

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• B-scans produce 2-D or 3-D images.

Describe and explain the principles of a B-scan

• Ultrasound is reflected at the boundary between materials;

• The B-scan takes place in different directions;

• The intensity of the reflected ultrasound depends on the acoustic impedances of the

materials, and this is greater when the difference between acoustic impedances is

greater.

Suggest why it is desirable to have ultrasound of short wavelength for a scan

• Using smaller wavelengths allow finer details to be seen and provides greater resolution.

Explain a method using ultrasound to determine the speed of blood in an artery in the arm

• The transducer is placed at an angle to the artery;

• ultrasound pulses are reflected by moving blood cells;

• The frequency (Wavelength) of ultrasound is changed

• This change in frequency (Wavelength) is related to the speed of blood.

What factors affect the acoustic impedance

• The density of the medium

• The speed of ultrasound in the medium

Medical Physics: Nuclear Medicine

Explain what is meant by a medical tracer

• A radioactive substance is injected into the patient;

• Which is then absorbed by the organ/tissue.

Give an example of a medical tracer that is commonly used to diagnose the function of organs

• Technetium-99m;

• Iodine-131;

• Fluorine-18;

• NOT Barium.

Name and describe the function of the main components of a gamma camera

• The collimator / lead tubes - gamma ray photons travel along the axis of the lead tubes;

• Scintillator / sodium iodide crystal - the incident gamma ray photon produces many

photons of visible light;

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• Photomultiplier tubes / photocathode and dynodes – An electrical pulse is/electrons

produced by the photons of visible light;

• Computer – Signals/electrons from the photomultiplier tubes are used to generate an

image.

State how the quality of the image produced by a gamma camera can be improved

• The quality of the image is improved by using thin/narrower or longer collimators, or a longer

scanning time.

Explain the basic principles of PET scanning, including how the image is formed

• The brain/body is surrounded by a ring of gamma cameras/detectors;

• The positrons from the F-18 nuclei annihilate electrons;

• The annihilation of a positron and an electron produces two identical gamma photons,

which travel in opposite directions;

• The delay time between the detection of these two photons in the gamma cameras is

used to determine the location of the annihilation (which are areas of increased activity);

• A computer is connected to the gamma cameras/detectors and an image is formed by the

computer using the electrical signals from the detectors.

Describe the operation of the MRI scanner with particular reference to the:

• Larmor frequency of the protons;

• resonance of the protons;

• relaxation times of the protons.

• Protons have a net spin and so they behave like tiny magnets;

• protons precess around the strong magnetic field which is provided by the strong

electromagnet;

• The frequency of precession is known as the Larmor frequency;

• Transmitting coils provide pulses of radio waves of frequency that is equal to the Larmor

frequency;

• The protons absorb energy from the radio waves, resonate and enter into a higher

energy state (they become excited);

• When the Pulse is off protons return back to their low energy state (that is when they

relax), they emit photons of radio frequency;

• The relaxation time is the average time taken for the protons to return back to their low

energy state after being excited;

• The relaxation time of the protons depends on the surrounding tissue;

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• A computer processes all the signals from the receiving coils and using computer

software, a 3D image is generated.

Diagnostics of internal organs

• Use of non-uniform/gradient field

• To locate positon of nuclei in body

State advantages of a MRI scan

• Non-ionising and non-invasive;

• Better contrast between soft tissues than CAT scan

•

State disadvantages of a MRI scan

• Patients with metallic objects cannot be scanned, such as those with cardiac pacemakers;

• Patient has to remain still for a long time;

• Scan takes place in a confined space, which is difficult for claustrophobic patients;

• Produces an unpleasant loud noise.

Discuss the major differences between an MRI scan and a PET scan of the brain

• PET scans use radioactive substances such as F-18 / MRI scans do not use radioactive

substances;

• PET scans reveal the function of the brain (they can diagnose dyslexia and

Alzheimer's disease);

• MRI scans show variation in the tissues (in the brain);

Cosmology Evolution of Stars and stellar fusion

Describe briefly the sequence of events which occur in the formation of a star, such as our

Sun, from interstellar dust and gas clouds and its most probable evolution

• Interstellar dust and gas clouds are drawn together by gravitational forces;

• The loss in gravitational potential energy increases the temperature of the gas;

• Fusion of protons occurs at a temperature of about 107

• Energy is released from the fusion reactions, where protons fuse together into helium;

• A stable star is formed when the gravitational pressure is equal to the radiation pressure.

• When the hydrogen is used up the outer layers of the star expand whilst the core

contracts

• A red giant is formed and it eventually becomes a white dwarf star

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Describe and explain the evolution of a star much more massive than our Sun

• When the hydrogen / helium fuel runs out in the star, the outer layers of the star expand,

and the core collapses rapidly forming a supernova

• Depending on the initial mass of the star, the remnant is either a neutron star or a black

hole.

Explain what is meant by fusion

• Fusion is the joining together of lighter nuclei in order to make heavier nuclei;

• This process releases energy as the total mass before the reaction is larger than the total

mass after the reaction.

Explain nuclear fusion and the conditions necessary for it to occur in the core of a star e.g. The Sun

• Protons/Hydrogen Nuclei fuse together to form He Nuclei

• There is electrostatic repulsion between protons due to their positive charge

• High temperatures of the order 107 K are needed for fusion to occur;

• High pressures/Density are required in the core;

• The protons within the core repel each other because they have like charges;

• When the nuclei are close enough, the strong nuclear force causes the protons to fuse

together and release energy.

Name two forms of energy produced in thermonuclear reactions

• Kinetic energy;

• Electromagnetic energy / photons.

Explain why a star of similar mass to the Sun is brightest when it is at the coolest temperature during its

evolution and why it is at its coolest

• The star will be a red giant;

• The star is cooler at this point, but it has a large surface area and so radiates a large

amount of energy, making it very bright.

• Surface Temperature decreases because work done expanding

Describe some of the characteristics of a white dwarf

• Extremely dense, very hot and low luminosity (counted as one characteristic);

• No fusion reactions occur;

• It is the remnant of a low-mass star;

• The mass of the star is below Chandrasekhar's limit, so the star cannot collapse and

overcome the electron degeneracy pressure to form a neutron star/black hole.

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One of the possible remnants of a supernova event is a black hole. State the properties of a black hole

• very dense;

• very strong gravitational field, so that light cannot escape from it;

• curves space;

• slows down time;

• Emits Hawking radiation.

Hubble, Olber’s Paradox, the big bang and the fate of the universe

State Olber’s' paradox

• The night sky should have uniform brightness, but it doesn't;

• The line of sight in any direction should end on the surface of a star.

State the two assumptions made about the universe in Olber's paradox

• The universe is infinite / is infinitely old;

• The universe has matter / stars distributed evenly throughout.

Describe an absorption spectrum

• Dark lines / bands (where particular wavelengths have been absorbed);

• Against a background of continuous spectrum.

State what is meant by the big bang

• The creation of the universe, from which space and time evolved.

Explain why galaxies do not collapse on each other

• The galaxies are moving away from each other due to the big bang;

• The acceleration between galaxies is too small to cause them to collapse.

• Other galaxies may be pulling in opposite direction

Explain how Hubble's Law resolves Olbers' paradox

• The universe is finite in its size and it is expanding;

• As the universe is expanding, it must have been smaller in the past and therefore had a

beginning where it was extremely small, and so cannot be infinitely old;

• Visible light is red-shifted due to the expansion of space.

Describe qualitatively the evolution of the universe immediately after the big bang to the present day

• At the start the universe was very hot and extremely dense;

• all the fundamental forces of nature were unified into one;

• the first particles began to form: they were quarks and leptons;

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• there was (and still is) more matter than antimatter in the universe;

• expansion of the universe led to cooling;

• the quarks combined to form hadrons;

• atoms formed once the universe had cooled further;

• the gravitational force of attraction between clouds of gas and dust caused stars and then

galaxies to form;

• The universe has continued to expand and cool to its present state of 2.7 K.

Describe observations that directly support the idea of the big bang

• Spectra from galaxies show shift to longer wavelengths. This suggests galaxies are

moving away from the Earth;

• The more distant galaxies are moving away from the Earth faster than ones closer to

Earth;

• If the galaxies have always been moving away from each other, then they will have been

much closer in the past;

• The existence of a (2.7K) microwave background radiation, which is the same intensity in

all directions, supports the big bang model of the universe, as the initial gamma radiation

in the universe has red shifted microwaves radiation as the universe expanded;

• There is more helium in the universe than expected shows the universe must have been

hot enough for fusion to have occurred in history amount of helium gives an idea of how

long it was hot enough for fusion

State some properties of the microwave background radiation observed from the Earth

• The intensity of the microwaves is the same in all directions;

• These microwaves correspond to a temperature of 2.7 K

Discuss how the microwave background radiation is linked to the big bang model of the universe

• The expansion of the universe following the big bang led to cooling and so we observe microwave radiation rather than short wavelength radiation such as gamma waves

• The intensity of the microwaves is the same in all directions (Isotropic)

• These microwaves correspond to a temperature of 2.7K

Describe how the big bang explains the origin of the microwave background radiation

• At the start, the universe was very hot;

• expansion of the universe led to cooling;

• the current temperature of the universe is 2.7 K;

• The universe, as a black body, is associated with microwaves at this temperature.

Describe how the microwave background radiation supports the cosmological principle

• The cosmological principle is supported because the microwave background is isotropic.

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Explain what is meant by the critical density of the universe

• The critical density is the density for which the universe will expand towards a finite limit

• the rate of expansion will tend to zero;

• And the result will be a flat-universe.

State the fate of the universe if its density is equal to the critical density

• Flat universe, so the universe will expand towards a limit / the rate of expansion will

become zero.

State the fate of the universe if its density is less than the critical density

• Open universe, so the universe will expand forever.

State the fate of the universe if its density is greater than the critical density

• Closed universe, so the universe's expansion will slow down and stop, and then the

universe will begin to collapse back down to a single point under the action of gravity.

Suggest reasons why it is difficult to predict the future of the universe

• The existence of dark matter, black holes, neutrinos and dark energy;

• Hubble's constant is not known to a high enough precision.

Suggest how the microwave background radiation may evolve in the future

• In an open (or flat) universe, further expansion will lead to the temperature decreasing

below 2.7K

• The wavelength of the EM radiation will then increase, and the microwaves will become

radio waves.

Jamie suggests that a star within our galaxy, moving towards us can be calculated using Hubble’s Law

discuss whether he is correct

• No Hubble’s Law can only be used on galaxies receding from us (and not on stars within

our own galaxy)

Explain why our understanding at the very earliest moments of the universe is unreliable

• No experimental Evidence/No Physical Evidence

• State of matter unknown/Laws of Physics Unknown

• Energies are not reproducible/Very High temperature