Past Paper Qu Flashcards
(25 cards)
Describe the operation of a MRI scanner
Protons/nuclei have spin, meaning they behave like tiny magnets
Protons process around the magnetic field (provided by the electromagnet)
The frequency of this procession is known as the Larmor frequency
Transmitting coil provides pulses of radio waves equal to the Larmor frequency
Protons resonate and enter higher energy state
When they relax the emit photons of radio waves
The relaxation time is the average time taken for them to relax back to their low energy state
The relaxation time depends of the tissue
Describe the operation of at CAT scanner
X ray beam is passed through the patient at different angles
A THIN fan shaped beam is used
Produces an image of that slice of the patient
X ray detectors are moved along for next slice
They produce a better contrast between soft tissues than an x ray, also 3D image
Describe how a star forms
Dust clouds are drawn together by gravitational forces over time
Loss in PE means they increase in KE so temp increases
Fusion of protons/hydrogen nuclei takes place under the heat
Energy is released in fusion reaction
A stable star is formed when gravitational pressure is equal to the radiation pressure/ force due to fusion
Describe some characteristics of a white dwarf
Extremely dense
Low luminosity
No fusion occurs
Is a remnant of a low mass star
State Olbers paradox and explain two assumptions about the universe
The night sky should have uniform brightness
Number of stars is proportional to r^2 and intensity to 1/r^2
Assuming infinite, static, uniformly distributed matter/stars
State Hubbles law and explain how it resolves Olbers paradox
Speed of recession of galaxy is equal to its distance from the earth
The universe is finite
Visible light is red shifted due to this expansion
Describe the principles of PET
Positron emitting subject is injected into the patient
Annihilation of electron and positron
This produces two gamma rays at 180 degrees
Patient surrounded by a ring of gamma detectors
Delay times used to calculate position
A 3D image is created
Describe how high frequency ultrasound can help tell the speed of blood through a patient
Ultrasound device emits and detects ultrasound
It is placed at an angle to the artery
Ultrasound is reflected by the blood cells
Change is frequency is measured and using that the speed of the blood can be calculated.
Bing bang
two points for evidence
Creation of an expanding universe that started from a very hot very dense singularity.
Background radiation
Existence of primordial helium
Tiny variations in background temperature.
Name and describe the main components of a gamma camera
Collimator and gamma ray photons travel along the axis of lead tubes
Scintillator and gamma photon produces many photons of light
Photomultiplier tubes and dynodes -pulse/signal/electrons produced by
photons of visible light
Computer signals are used to generate an image
QWC: Quality of image improved by
narrower / thinner / longer collimators OR longer scanning
time
Desceibe what is meant by the big bang and it explains the origin of cosmic microwave backroud radiation
Creation of the universe from which space and time evolved
At the start it was hot, infinitely dense
Expansion led to cooling
Current temperature is 3k
The gamma radiation from the big bang ahas been stretched to microwaves by the expansion
QWC - MBR is isotropic which supports the cosmolgical principle
Explain why the total mass of individuals nucleons in hydrogen 2H1 is different from the mass of it in reality
Mass of the nucleus is less than the mass of the nucleons
Energy released when nucleons combine
E=mc2 and e is the binding energy is the mass difference
Explain in terms of the movement of electrons how X and Y acquire opposite charge
Electrons accumulate on Y
Y becomes negative
An equal number of electrons that are deposited on Y are repelled of X so the equal but opposite charge.
Explain what is meant by the term induced nuclear fission
Where a thermal nucleon collides with a nucleus casuing it to split up into two parts and fast moving neutrons
Explain the purpose of control rods and the moderator in a nuclear reactor
Fission produces fast neutrons
The moderator slows down the neutrons
Slow moving neutrons have a better chance of causing fission
The control rods absorb neutrons
So only one remains from every collision so no chain reaction occurs
QWC The neutrons collide with the moderator nuclei and transfer their kinetic energy
Describe and explain the principle of B scans
Ultrasound reflected at boundaries between materials
B-scan takes place in different directions or is multiple A scans
QWC the intensity of the reflected ultrasound depends on the acoustic impedance
State some of the properties of the microwave radiation observed from earth, discuss how the background microwave radiation is linked to the big bang
It is observed in every direction at the same intensity
The temperature of the universe is 2.7K
Gamma rays from the big bang have been stretched ( red shifted) over time to microwaves
Electric field strength is a a vector
Two positive charges have opposite E’s
The process of nuclear fusion in the core of the sun
Hydrogen nuclei fuse together to produce helium nuclei
The electrostatic force of attraction has to be overcome
requires temperatures up to 10^7 K
The mass loss (binding energy) in converted in evergy
E=mc^2
High pressure and density
At high temperatures some protons fuse by overcoming the electrostatic force of replusion
Formation of a star such as the sun
Gas cloud drawn together by gravitational forces
Loss in PE means a increase in KE
Fusion of hydrogen nuclei occur when KE is large enough
A stable star is formed when radiation pressure is equal to gravitational pressure
When stars run out the core shrinks
Red giant formed which eventually becomes a white dwarf
Ways which X ray photons react with matter 3
The photoelectric effect where a orbital electron is ejected from an atom
Compton scattering where x-ray scattered by interaction with longer wavelength and electron scattered
Pair production is where a X ray photon interacts with the nucleus of an atom and an electron and a positron are produced
Using a image intensifier
Absorption of x rays by a photographic film
Use of scintillator which converts one x ray photon into many visible light photons
Photon releases electron that is accelerated into a fluorescent screen
Photon reaches a photoelectric substance that releases an electron which is detected by a computer and intensity and software used to create image
Nature and range of forces acting on protons and nuetrons
Gravitational force, attractive
and is long ranged
Strong nuclear force, attractive at longer distances and repulsive at shorter distances
and is short ranged
Electrostatic force is repulsive between protons and zero between neutrons
And is long ranged
1 pc
3*10^16m
