A-Level Physics G485 Flashcards
1
Q
Define Electric Field Strength
A
Electric field strength at a point in space is the force per unit positive charge
2
Q
Define Magnetic Flux Density
A
a measure of the strength of a magnetic field at a given point, expressed by the force per unit length on a conductor carrying unit current at that point.
3
Q
Define Tesla
A
One Tesla is the uniform magnetic flux density which, acting normally to a long straight wire carrying a current of 1 ampere, causes a force per unit length of 1Nm-1 on the conductor.
4
Q
Define Magnetic flux
A
magnetic flux = magnetic flux density x area (perpendicular to field direction)
B x A (normal to B). Magnetic flux=magnetic field x Area
5
Q
Define The Weber
A
One Weber is equal to one Tesla metre²
6
Q
Define Magnetic Flux Linkage
A
The change of magnetic flux linkage is equal to the product of the change in magnetic flux and the number of turns N of a conductor involved in the change in flux
7
Q
Define Capacitance
A
Capacitance = charge per (unit) potential differences
Ratio of charge to potential for a conductor
8
Q
Define The Farad
A
coulomb per volt
A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt
9
Q
Define The Time Constant Of A Circuit
A
Time for the charge to have decreased to “1/e” of its initial charge
10
Q
Define Proton Number
A
The number of protons found in the nucleus of an atom
11
Q
Define Nucleon Number
A
The mass number, the sum of the number of neutrons and protons in an atomic nucleus
12
Q
Define Isotopes
A
Isotopes are different forms of the same element which have the same number of protons but different numbers of neutrons in their nuclei
13
Q
Define Activity (Radioactivity)
A
Spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
14
Q
Define The Decay Constant
A
The probability of decay of a nucleus per
unit time
Reciprocal of decay time
15
Q
Define Half Life
A
The half-life of a radioactive nuclide is the time taken for the number of un-decayed nuclei to be reduced to half its original number
16
Q
Define Binding Energy
A
The energy equivalent of the mass defect of a nucleus. It is the energy required to separate to infinity all the nucleons of a nucleus
17
Q
Define Binding Energy Per Nucleon
A
Binding energy per nucleon is defined as the total energy needed to completely separate all the nucleons in a nucleus divided by the number of nucleons in the nucleus
18
Q
Define Intensity
A
Power per unit area(W/m²)
19
Q
Define The Distance Measured In Astronomical Units (AU)
A
The astronomical unit is defined as the radius of the circular path round the sun followed by a body in 365.25 days
20
Q
Define The Distance Measured In Parsecs (pc)
A
Distance from a base length of 1 AU that subtends an angle of 1 (arc) second
21
Q
Define The Distance Measured In Light-Years (ly)
A
The distance travelled by electromagnetic radiation (light) in one year
22
Q
Define Critical Density
A
The average density of the universe
- Above which the universe will collapse (closed universe)
- Below which the universe will expand forever (open universe)
- If the density is equal to the critical universe get a flat universe.
23
Q
State that electric fields are created by electric charges
A
Electric charges exert forces on each other when they are a distant apart. An electric field is a region of space where a stationary charge experiences a force
24
Q
State and use Fleming’s left-hand rule to determine the force on a current conductor places at right angles to a magnetic field.
A
If the first two fingers and thumb of the left hands are placed at right angles then the first finger is in the direction of the field, the second in the direction of the current and the thumb in the direction of motion
25
State and use Faradays Law of electromagnetic induction
Induced e.m.f is proportional to the rate of change of (magnetic) flux
26
State and use Lenz’s law
The direction of the induced e.m.f is such as to cause effects to oppose the change producing it
27
State and use the equation for the total capacitance of two or more capacitors in parallel
C= C1+C2+C3.......
28
State and use the equation for the total capacitance of two or more capacitors in series
1/Ct =1/C1+1/C2+1/C3 ......
29
State the quantities conserved in a nuclear decay
The charge, the total number of neutrons and protons, total energy, the total momentum of the system and the total lepton number.
30
State that there are two types of β decay
β- decay produces an emission of electrons. (Electron) antineutrinos are produced.
A β- particle IS an electron.
β+ decay produces an emission of positrons. (Electron) neutrinos are produced.
A β+ particle IS a positron.
31
State which Group electrons and neutrinos are members of.
Electrons and neutrinos are members of a group of particles called "Leptons".
(There are six members of this group in all, the Electron, Muon and Tao, and their associated neutrinos)
32
State the approximate magnitude of the parsec in meters
3.1 x 1013km
_or_
3.1 x 1016m
33
State the approximate value in meters of the light year.
9 x 1015m
(sometimes it is taken to be
10 x 1015 the true value is
9.46 × 1015 [to 3sf])
34
State Olbers’ paradox
Based on: the universe being static, homogeneous and infinite - there should be an infinite number of stars visible (the night sky should be as bright as at day).
35
State and interpret Hubble’s law
All objects observed in deep space (intergalactic space) are found to have a Doppler shift observable relative velocity to Earth, and to each other; and that this Doppler-shift-measured velocity, of various galaxies receding from the Earth, is proportional to their distance from the Earth and all other interstellar bodies.
The interpretation of this law is that the universe is expanding.
36
State the cosmological principle
On large enough scales the universe is isotropic and homogenous. That is that there is no "special" point in the universe and no discernable centre.
37
Explain the effect of a uniform electric field on the motion of a charged particle
If E is uniform, then the acceleration of the charged particle is constant. If the particle has a positive charge, then its acceleration is in the direction of the electric field. If the particle has negative charge, then its acceleration is in the direction opposite the electric field
38
Explain the use of deflection of charged particles in the magnetic and electric fields of a mass spectrometer
Depending on the strength of the magnetic and electric fields the mass of charged particles detected can be changed. E.g: the smaller the electric field the larger massed particles can be detected
39
What does the area under a potential difference vs charge graph represent.
It is equal to the energy stored bvy a capacitor.
40
Explain the propertiers of an exponential decay graph
At first gradient is large in magnitude and this gradient then decreases in magnitude over time. THE MOST IMPORTANT property of exponential decay graphs is that they have a constant ratio property, in a certain time "t" they will always decay to half the previous value.
41
Explain why Protons and neutrons are not fundamental particles.
Protons and Neutrons (as well as all mesons and hadrons) are made of smaller constituent particles called "Quarks", and so are not fundamental particles.
42
Explain how soft tissues like the intestines can be imaged using barium meal
In order to make soft tissue more visible, contrast media, such as barium, are used. The patient swallows a liquid rich in barium as it will readily absorb X-rays. The barium meal coats the wall of the tract enabling its outline to be seen in X-rays
43
Explain what is meant by the Doppler effect
Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave and whatever is measuring, seeing or hearing the wave.
44
Explain qualitatively how the Doppler effect can be used to determine the speed of blood
Doppler effect uses ultrasound waves. Sound waves are reflected by the moving blood cells. Change in frequency/wavelength enables the speed of blood flow or rate of flow of blood to be found
45
Explain how ultrasound transducers emit and receive high frequency sound
Transducer is the name given to any device that converts energy from one form to another. In this case electrical energy is converted into ultrasound energy by means of a piezo-electric crystal such as a quartz
46
Explain that the standard model of the universe implies a finite age for the universe (hot big bang)
galaxies are moving apart / universe is expanding
if galaxies have always been moving apart then at some stage they must have been closer together / or started from a point
evidence in red shift either optical / microwave
further away the galaxy the faster the speed of recession
the existence of a (2.7 K) microwave
background radiation
there is more helium in the universe than expected
47
Explain that the universe can be ‘open’, ‘flat’ or ‘closed’, depending on its density
Open: Universe expands for all time
Flat: expands to a limit (but never reaches it)
Closed: Universe contracts / collapses
back
48
Explain that the ultimate fate of the universe depends on its density
if average density of the Universe is less than critical then it will be too small to stop it expanding / it goes on forever
if the average density of the Universe is greater than the critical value it will cause the contraction (and produce a big crunch)
close to critical value and therefore a universe expands that will go towards a limit / expands at an ever decreasing rate asymptotic
49
Explain that it is currently believed that the density of the universe is close to, and possibly exactly equal to, the critical density needed for a ‘flat’ cosmology
*p*0 = 3(H0)2/8πG
Estimates give values of 1 or 2 orders of magnitude less than critical. But rotation of galaxies show they have more mass than we can see, and the inflationary expansion theory suggests that the density is exactly equal to critical
50
Describe the difference between A-scan and B-scan
A-scan in one direction only / range or distance or depth finding
B-scan uses a number of sensors or a sensor in different positions / angles (to build up a 2D/3D image)
51
Describe the importance of impedance matching
There is a large difference in density between air and skin/fat/flesh. Because of this large difference roughly 99% of the Ultrasound would be reflected, resulting in a poor quality image. By use of a gel of similar "acoustic impedance" to the human body Ultrasound will transmit into the body and return to the transducer so an image can be processed
52
Describe the principle contents of the universe, including stars, galaxies and radiation
There are at least 1010galaxies in the universe. From a side view there is a disc shaped conglomeration of stars with a bulging central nucleus
53
Describe the solar system in terms of the Sun, planets, planetary satellites and comets
Solar system contains 9 well known planets and their satellites; it also contains a number of small or dwarf planets. These planets all orbit the sun. Comets have an elliptical orbit, which means that they return regularly often passing close enough to the earth to be visible
54
Describe the formation of a star, such as our Sun, from interstellar dust and gas.
1. Gas / dust (cloud) drawn together by gravitational forces
2. Loss in (gravitational) PE / KE increases / PE changes KE / temperature increase
3. Fusion of protons / hydrogen nuclei (produces helium nuclei and energy)
4. A stable star is formed when radiation pressure is equal to gravitational pressure
55
Describe the Sun’s probable evolution into a red giant and white dwarf
Sun is on the main sequence but becoming redder, it will take 5x109 years before becoming a red giant
In the red giant stage no further energy can be obtained so the star will shrink under its internal gravitational attraction. As it gets smaller emitted radiation becomes whiter, it now becomes a white dwarf
56
Describe how a star much more massive than our Sun will evolve into a super red giant and then either a neutron star or black hole.
Supernova followed by neutron star / black hole
Great mass, so the core collapses under its gravity. The KE and temperature are so high that fusion takes places; there is enough energy to turn electrons and protons into neutrons. Core contracts until it becomes entirely neutron, it is then a neutron star (high density)
However gravitation force on neutrons could become so strong it prevents the light being emitted, no radiation emitted means it will appear black, this is a black hole.
57
Describe and interpret Hubble’s red shift observations
Observations that the wavelengths of identifiable spectral lines in the spectra of light from distant galaxies did not correspond with wavelength measured on earth. Column of light seemed to be shifted towards the red end of the spectrum. This was interpreted as a continuous expansion of the universe
58
Describe and explain the significance of the 3K microwave background radiation
The 3K CMB radiation is a remnant of the "Big Bang". The early universe was very energetic and "hot". It was enhabited by high energy gamma rays, as the universe expanded these gamma rays were redshifted so that their wavelength was increased and their energy and frequency reduced. This energy now exists as microwaves which pervade the whole universe.
59
Describe qualitatively the evolution of universe 10-43s after the big bang to the present
10-43s temperature was high 1032K and any particles will be moving with average KE of 1019GeV
At 10-43s Change occurred; gravitational force appeared as a separate force. Still no distinction between quarks and leptons 10-35s
The universe had expanded, the temperature fallen to 1027K, strong nuclear force distinguished as were quarks and leptons. Leptons included electrons, neutrinos and all corresponding antiparticles. Quarks were initially free but soon began to form nucleons and hadrons
## Footnote
10-6s Temperature fell to 1013K, average KE was insufficient to create particle-antiparticle pairs from nucleons. Annihilation continued leading to a universe with far fewer nucleons and more particles than antiparticles
60
Describe how electric field lines represent an electric field
The direction of the electric field is defined as the direction in which a positive charge would move if it were free to do so. So the lines of force can be drawn with arrows that go from positive to negative
61
Describe the similarities and differences between the gravitational fields of point masses and the electric fields of point charges
Both fields decrease in magnitude as the distance from the point charge/mass decreases in accordance with the r2 law.
The magnitude of an electric field depends on the amount of charge, the magnitude of a gravitational field depends on the amount of mass.
Electric fields are in general stronger than gravitational fields because the gravitational constant is much smaller than its equivalent.
62
Describe the magnetic field patterns of a long straight current-carrying conductor and a long solenoid
Magnetic field patterns due to a long straight wire are concentric circles centred on the middle of the wire. The separation of the line increases with distance from the wire.
A solenoid may be thought to be made up of many flat coils placed side by side. The field lines are parallel and equally spaced over the centre section of the solenoid indicating the field is uniform
63
Describe the function of a simple ac generator
An electric generator converts mechanical energy in the form of the rotation energy of a coil of wire into electrical energy. This occurs as the coil is rotated in a magnetic field, the change in magnet field induces an e.m.f. which produces a current in the coil.
64
Describe the function of a simple transformer
A simple transformer is two coil of insulated wire wound on to a laminated soft iron core. And alternating e.m.f is applied across the primary coil and an e.m.f is induced in the secondary
65
Describe the function of step-up and step-down transformers
Step up- when Vs is greater than Vp there are more turns in the secondary coil than the primary. Low to high voltage
Step down- when Vs is less than Vp there are more turns in the primary coil than the secondary. High to low voltage
66
Describe the uses of capacitors for the storage of energy in applications such as flash photography, lasers used in nuclear fusion and as back-up power supplies for computers
Capacitor takes a few seconds to charge then it is either discharged rapidly when connected to the flash bulb to give a short but intense flash, or it can be released slowly, when being used as a back up battery
67
Describe qualitatively the alpha-particle scattering experiment and the evidence this provides for the existence, charge and small size of the nucleus
α - particle scattering
suitable diagram with source, foil, moveable detector
2 or more trajectories shown
vacuum
most particles have little if any deflection
large deflection of very few
reference to Coulomb’s law /elastic scattering
alphas repelled by nucleus (positive charges)
monoenergetic
OR electron scattering
High energy diagram with source sample, moveable detector / film
Vacuum
Electron accelerator or other detail
Most have zero deflection
Characteristic angular distribution with minimum
Minimum not zero
De Broglie wavelength
68
Describe the basic atomic structure of the atom and the relative sizes of the atom and the nucleus
Protons are in the nucleus they have a mass u and charge +e
Neutrons are also in the nucleus they do not have a charge and have a mass u
Electrons orbit the nucleus and have mass u/2000 and a charge -e
69
Describe how the strong nuclear force between nucleons is attractive and very short-ranged
Due to a strong force that binds quarks together to form neutrons and protons. Must be short range as it does not influence beyond the nuclear surface and strong enough to overcome the repulsive force of the protons.
70
Describe a simple quark model of hadrons in terms of up, down and strange quarks and their respective antiquarks, taking into account their charge, baryon number and strangeness.
There are three quarks with corresponding antiquarks. They have a fractional charge of either 1 or 2 thirds.
Baryons are made up of three quarks
Mesons are small and made of a quark and antiquark
71
Describe how the quark model may be extended to include the properties of charm topness and bottomness
3 more quarks called charmed, bottom and top.
Charmed quarks have a charge +2e/3 and a baryon number of 1/3
Bottom quarks have a charge of –e/3 and a baryon number of 1/3
Top quarks have a charge of +2e/3 and a baryon number of 1/3
72
Describe the properties of neutrons and protons in terms of a simple quark model
Neutrons- No charge, mass u, made of 1 up and 2 down quarks
Protons-+1 charge, mass u, made of 2 up and 1 down quark
73
Describe how there is weak interactions between quarks and that this is responsible for ß decay
Because of weak interactions between quarks a down quark is able to become an up quark turning a neutron into a proton and emitting an electron
74
Describe the two types of ß decay in terms of a simple quark model
β- decay a down quark turns into an up quark, this results in a neutron turning into a proton and emits an electron and an anti-electron neutrino (to conserve charge and lepton number)
β+ decay an up quark turns into a down quarkm, this meas that a proton turns into a neutron and a positron is emitted along with an electron neutrino
75
Describe the spontaneous and random nature of radioactive decay of unstable nuclei
Spontaneous: the decay cannot be induced / occurs without external influence
Random: cannot predict when / which (nucleus) will decay next
76
Describe the nature, penetration and range of α particles, ß particles and γ rays
Alpha particles are helium nuclei, have a charge +2e and cantravel through a few cm of air
## Footnote
Beta emissions are fast moving electrons, each has a charge of –e and can penetrate a few mm of aluminium
Gamma rays are electromagnetic radiation, as such they have no charge and penetrate a few cm of lead
77
Describe the use of radioactive isotopes in smoke alarms
Ionisation of air caused by a small alpha particle emitter with a long half-life, the alpha particles pass between electrodes producing a current. If there is more than a certain concentration of smoke alpha particles are absorbed and the current is then reduced, this then triggers the alarm
78
Describe the nature of x-rays
Composition of electric and magnetic fields which move perpendicular to each other
79
Describe in simple terms how x-rays are produced
Firing high energy particles at a metal target results in collisions. These collisions are inelastic and some of the KE is transfered into X-ray radiation. The most powerful radiation is produced when the particles collide "head on" as this is where the largest loss of KE occurs.
80
Describe how x-rays interact with matter (limited to the photoelectric effect, Compton effect and pair production)
Some of the photons interact with the particles of the matter and their energy can be absorbed or scattered, others do not interact. The number of photons transmitted depends on thickness and density
81
Describe the use of x-rays in imaging internal body structures including the use of image intensifiers and of contrast media
Intensifier used as X-ray would pass through film
Intensifier converts X-ray photon to many visible (light) photons (which are absorbed by film)
Lower exposure / fewer X-rays needed
Iodine / barium (used as contrast material)
High Z number / large attenuation coefficient / large absorption coefficient (used to improve image contrast)
Contrast media are ingested / injected into the body
Absorption of X-rays by (silver halide molecules) by a photographic film
Uses of fluorescent / scintillator/ phosphor
Photon releases electron (that is accelerated onto a fluorescent screen)
number of electrons increased /multiplied
82
Describe the operation of a computerised axial topography (CAT) scanner
Series of c rays obtained through a section of body from a different angle, the computer recreates a 3D image
83
Describe the advantages of a CAT scan compared with an x-ray image
Differences: Simple X-ray is one directional / produces single image
Simple X-ray is one directional / produces single image
Computer processes data / image constructed from many slices
Advantages: X-ray image is 2D / CT scan produces 3D image
Greater detail / definition / contrast with CT scan / ‘soft tissues can be seen’
Image can be rotated
84
Describe the use of medical tracers like technetium-99m to diagnose the function of organs
Tracer administered will be giving off radiation so the path can be followed. It will not interfere with any functions of the body. And it must emit detectable radiation so that the image of the organs can be observed
85
Describe the main components of a gamma camera
Photon passed into a photomultiplier tube where it falls on a photocathode emitting an electron, which is accelerated towards a dynode. The dynode emits several electrons which are then accelerated and repeated multiple times and can then be amplified and processed
86
Describe the principles of positron emission tomography (PET)
1. A positron / beta-plus emitting tracer / source is used
2. The positron annihilates with an electron (inside the patient)
3. This produces two gamma photons
4. The photons travels in opposite directions
5. The patient is surrounded by a ring of gamma detec-tors
6. The arrival times of the photons / delay time indicates location (of tumour inside the body)
7. A 3-D image is created (by the computer connected to the detectors)
87
Describe the main components of an MRI scanner
**Superconducting Magnet** - Provides the strong magnetic field of flux density about 2 T.
**Radio-frequency (RF) transmitter coil** - Transmits Radio-frequency (RF) pulses into the patient.
**RF receiver coil** - Picks up the radio waves emitted by the nuclei returning to their low-energy state.
**Gradient coils** - Produce an additional external magnetic field along the length, depth and width of the patient. The Larmor frequency is therefore different for each part of the body.
**Computer** - Controls the radio-frequency pulses from the RF transmitter coils and analyses the signals from the RF receiving coils. The location of the tissues is pinpointed by the slightly different Larmor frequencies due to the gradient coils. The type of tissue is identified from the different relaxation times. The computer produces images (slices) through the patient and gives a detailed 3D image
88
Describe the advantages and disadvantages of MRI
Advantage: not ionising radiation (as with X-rays) / better soft tissue contrast
Disadvantage: heating effect of metal objects /effect on cardiac pacemakers / takes a long time to perform MRI scan
method does not use ionising radiation
hence no radiation hazard to patient or staff
89
Describe the need for non invasive techniques in diagnosis
No surgery, less infections. Easy to monitor health with minimal harm to the body. Also allows more time to observe the body.
90
Describe the properties of ultrasound
The typical frequency of ultrasound used in medical imaging is 2 MHz. The wavelength can be as small as 1mm so smaller details are detected by the scan. the speed of the ultrasound is depends on the material it is travelling through.
The gel allows maximum transmission of ultrasound (into the body).
91
Describe the piezoelectric effect
The application of a p.d. across a material / crystal causes an expansion / contraction / vibration
92
Describe the principles of ultrasound scanning
Pulses of ultrasound (sent into the body)
Wave / ultrasound / pulse / signal is reflected (at boundary of tissue)
Time of delay used to determine depth / thickness
The fraction of reflected signal is used to identify the tissue
Small wavelength used which means finer detail can be seen / greater resolution
93
Describe the process of induced nuclear fission
The splitting of a heavy nucleus into two lighter nuclei of approximately the same mass
94
Describe the techniques of radioactive dating
Living plants / animals absorb carbon(-14)
Once dead, the plant does not take in any more carbon(-14)
The fraction of C-14 to C-12 (nuclei) or number of C-14 (nuclei) or activity of C-14 (nuclei) measured in dead and living (sample)
## Footnote
x = x0 e-(labda)t used with data above to estimate the age
95
Describe and explain the process of nuclear chain reaction
Occurs when one nuclear reaction causes an average of one of more nuclear reactions, thus leading to a self-propagating series of reactions
96
Describe the basic construction of a fission reactor and explain the role of the fuel rods, control rods and the moderator
Reactor core holding the fission fuel. Moderator for slowing fast neutrons. Control rods to control the rate of fission by absorbing excess electrons. A monitoring system. Energy transfer system to take heat away
97
Describe the use of nuclear fission as an energy source
Advantages-does not produce acid rain or waste gases which cause pollution
-provides energy for nuclear power and can provide electricity
Disadvantages-problems with the reaction getting out of control
-risks from radiation
-long half life of waste
-can be used to drive nuclear weapons
98
Describe the peaceful and destructive uses of nuclear fission
Peaceful-Create Energy
Destructive-Nuclear Weapons
99
Describe the environmental effects of nuclear waste
Nuclear waste in water can contaminate wildlife, especially if it is still highly radioactive
100
Describe the process of nuclear fusion
Two or more atomic nuclei join together to form a single heavier nucleus, accompanied by the release of large quantities of energy
101
Describe the conditions in the core of stars
Fusion in the core of the sun: Protons / hydrogen nuclei to produce Helium nuclei (positrons and neutrinos)
There is electrostatic repulsion (between the protons) / The protons repel (each other because of their positive charge)
High temperatures / 107 K needed (for fusion
(At high temperatures some of the fast moving) protons come close enough to each other for the strong (nu-clear) force (to overcome the electrostatic repulsion) High density / pressure (in the core of the Sun) There is a decrease in mass, hence energy is released / products have greater binding energy
102
Analyse the circular orbits of charged particles moving in a plane perpendicular to a uniform magnetic field by relating the magnetic force to the centripetal acceleration it causes
Consider positively charged particle of mass m carrying charge q and moving with velocity v, when it enters the magnetic field which is normal to the direction of motion of the particle it will experience a force normal to its direction. This does not affect speed but will change the direction of motion so the body moves in a circular motion
103
Analyse the motion of charged particles in both electric and magnetic fields
The force on a particle of charge q moving at speed v and an angle θ to a uniform magnetic field of flux density B is given by F=BqvSinθ
104
State the approximate magnitude of the parsec in meters
3.1 x 1013km
_or_
3.1 x 1016m
105
State the approximate value in meters of the light year.
9 x 1015m
(sometimes it is taken to be
10 x 1015 the true value is
9.46 × 1015 [to 3sf])
106
State Olbers’ paradox
Based on: the universe being static, homogeneous and infinite - there should be an infinite number of stars visible (the night sky should be as bright as at day).
107
State and interpret Hubble’s law
All objects observed in deep space (intergalactic space) are found to have a Doppler shift observable relative velocity to Earth, and to each other; and that this Doppler-shift-measured velocity, of various galaxies receding from the Earth, is proportional to their distance from the Earth and all other interstellar bodies.
The interpretation of this law is that the universe is expanding.
108
State the cosmological principle
On large enough scales the universe is isotropic and homogenous. That is that there is no "special" point in the universe and no discernable centre.
109
Explain the effect of a uniform electric field on the motion of a charged particle
If E is uniform, then the acceleration of the charged particle is constant. If the particle has a positive charge, then its acceleration is in the direction of the electric field. If the particle has negative charge, then its acceleration is in the direction opposite the electric field
110
Explain the use of deflection of charged particles in the magnetic and electric fields of a mass spectrometer
Depending on the strength of the magnetic and electric fields the mass of charged particles detected can be changed. E.g: the smaller the electric field the larger massed particles can be detected
111
What does the area under a potential difference vs charge graph represent.
It is equal to the energy stored by a capacitor.
112
Explain the propertiers of an exponential decay graph
At first gradient is large in magnitude and this gradient then decreases in magnitude over time. THE MOST IMPORTANT property of exponential decay graphs is that they have a constant ratio property, in a certain time "t" they will always decay to half the previous value.
113
Explain why Protons and neutrons are not fundamental particles.
Protons and Neutrons (as well as all mesons and hadrons) are made of smaller constituent particles called "Quarks", and so are not fundamental particles.
114
Explain how soft tissues like the intestines can be imaged using barium meal
In order to make soft tissue more visible, contrast media, such as barium, are used. The patient swallows a liquid rich in barium as it will readily absorb X-rays. The barium meal coats the wall of the tract enabling its outline to be seen in X-rays
115
Explain what is meant by the Doppler effect
Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave and whatever is measuring, seeing or hearing the wave.
116
Explain qualitatively how the Doppler effect can be used to determine the speed of blood
Doppler effect uses ultrasound waves. Sound waves are reflected by the moving blood cells. Change in frequency/wavelength enables the speed of blood flow or rate of flow of blood to be found
117
Explain how ultrasound transducers emit and receive high frequency sound
Transducer is the name given to any device that converts energy from one form to another. In this case electrical energy is converted into ultrasound energy by means of a piezo-electric crystal such as a quartz
118
Explain that the standard model of the universe implies a finite age for the universe (hot big bang)
galaxies are moving apart / universe is expanding
if galaxies have always been moving apart then at some stage they must have been closer together / or started from a point
evidence in red shift either optical / microwave
further away the galaxy the faster the speed of recession
the existence of a (2.7 K) microwave
background radiation
there is more helium in the universe than expected
119
Explain that the universe can be ‘open’, ‘flat’ or ‘closed’, depending on its density
Open: Universe expands for all time
Flat: expands to a limit (but never reaches it)
Closed: Universe contracts / collapses
back
120
Explain that the ultimate fate of the universe depends on its density
if average density of the Universe is less than critical then it will be too small to stop it expanding / it goes on forever
if the average density of the Universe is greater than the critical value it will cause the contraction (and produce a big crunch)
close to critical value and therefore a universe expands that will go towards a limit / expands at an ever decreasing rate asymptotic
121
Explain that it is currently believed that the density of the universe is close to, and possibly exactly equal to, the critical density needed for a ‘flat’ cosmology
*p*0 = 3(H0)2/8πG
Estimates give values of 1 or 2 orders of magnitude less than critical. But rotation of galaxies show they have more mass than we can see, and the inflationary expansion theory suggests that the density is exactly equal to critical
122
Describe the difference between A-scan and B-scan
A-scan in one direction only / range or distance or depth finding
B-scan uses a number of sensors or a sensor in different positions / angles (to build up a 2D/3D image)
123
Describe the importance of impedance matching
There is a large difference in density between air and skin/fat/flesh. Because of this large difference roughly 99% of the Ultrasound would be reflected, resulting in a poor quality image. By use of a gel of similar "acoustic impedance" to the human body Ultrasound will transmit into the body and return to the transducer so an image can be processed
124
Describe the principle contents of the universe, including stars, galaxies and radiation
There are at least 1010galaxies in the universe. From a side view there is a disc shaped conglomeration of stars with a bulging central nucleus
125
Describe the solar system in terms of the Sun, planets, planetary satellites and comets
Solar system contains 9 well known planets and their satellites; it also contains a number of small or dwarf planets. These planets all orbit the sun. Comets have an elliptical orbit, which means that they return regularly often passing close enough to the earth to be visible
126
Describe the formation of a star, such as our Sun, from interstellar dust and gas.
1. Gas / dust (cloud) drawn together by gravitational forces
2. Loss in (gravitational) PE / KE increases / PE changes KE / temperature increase
3. Fusion of protons / hydrogen nuclei (produces helium nuclei and energy)
4. A stable star is formed when radiation pressure is equal to gravitational pressure
127
Describe the Sun’s probable evolution into a red giant and white dwarf
Sun is on the main sequence but becoming redder, it will take 5x109 years before becoming a red giant
In the red giant stage no further energy can be obtained so the star will shrink under its internal gravitational attraction. As it gets smaller emitted radiation becomes whiter, it now becomes a white dwarf
128
Describe how a star much more massive than our Sun will evolve into a super red giant and then either a neutron star or black hole.
Supernova followed by neutron star / black hole
Great mass, so the core collapses under its gravity. The KE and temperature are so high that fusion takes places; there is enough energy to turn electrons and protons into neutrons. Core contracts until it becomes entirely neutron, it is then a neutron star (high density)
However gravitation force on neutrons could become so strong it prevents the light being emitted, no radiation emitted means it will appear black, this is a black hole.
129
Describe and interpret Hubble’s red shift observations
Observations that the wavelengths of identifiable spectral lines in the spectra of light from distant galaxies did not correspond with wavelength measured on earth. Column of light seemed to be shifted towards the red end of the spectrum. This was interpreted as a continuous expansion of the universe
130
Describe and explain the significance of the 3K microwave background radiation
The 3K CMB radiation is a remnant of the "Big Bang". The early universe was very energetic and "hot". It was enhabited by high energy gamma rays, as the universe expanded these gamma rays were redshifted so that their wavelength was increased and their energy and frequency reduced. This energy now exists as microwaves which pervade the whole universe.
131
Describe qualitatively the evolution of universe 10-43s after the big bang to the present
10-43s temperature was high 1032K and any particles will be moving with average KE of 1019GeV
At 10-43s Change occurred; gravitational force appeared as a separate force. Still no distinction between quarks and leptons
10-35s The universe had expanded, the temperature fallen to 1027K, strong nuclear force distinguished as were quarks and leptons. Leptons included electrons, neutrinos and all corresponding antiparticles. Quarks were initially free but soon began to form nucleons and hadrons
10-6s Temperature fell to 1013K, average KE was insufficient to create particle-antiparticle pairs from nucleons. Annihilation continued leading to a universe with far fewer nucleons and more particles than antiparticles
132
Describe how electric field lines represent an electric field
The direction of the electric field is defined as the direction in which a positive charge would move if it were free to do so. So the lines of force can be drawn with arrows that go from positive to negative
133
Describe the similarities and differences between the gravitational fields of point masses and the electric fields of point charges
Both fields decrease in magnitude as the distance from the point charge/mass decreases in accordance with the r2 law.
The magnitude of an electric field depends on the amount of charge, the magnitude of a gravitational field depends on the amount of mass.
Electric fields are in general stronger than gravitational fields because the gravitational constant is much smaller than its equivalent.
134
Describe the magnetic field patterns of a long straight current-carrying conductor and a long solenoid
Magnetic field patterns due to a long straight wire are concentric circles centred on the middle of the wire. The separation of the line increases with distance from the wire.
A solenoid may be thought to be made up of many flat coils placed side by side. The field lines are parallel and equally spaced over the centre section of the solenoid indicating the field is uniform
135
Describe the function of a simple ac generator
An electric generator converts mechanical energy in the form of the rotation energy of a coil of wire into electrical energy. This occurs as the coil is rotated in a magnetic field, the change in magnet field induces an e.m.f. which produces a current in the coil.
136
Describe the function of a simple transformer
A simple transformer is two coil of insulated wire wound on to a laminated soft iron core. And alternating e.m.f is applied across the primary coil and an e.m.f is induced in the secondary
137
Describe the function of step-up and step-down transformers
Step up- when Vs is greater than Vp there are more turns in the secondary coil than the primary. Low to high voltage
Step down- when Vs is less than Vp there are more turns in the primary coil than the secondary. High to low voltage
138
Describe the uses of capacitors for the storage of energy in applications such as flash photography, lasers used in nuclear fusion and as back-up power supplies for computers
Capacitor takes a few seconds to charge then it is either discharged rapidly when connected to the flash bulb to give a short but intense flash, or it can be released slowly, when being used as a back up battery
139
Describe qualitatively the alpha-particle scattering experiment and the evidence this provides for the existence, charge and small size of the nucleus
α - particle scattering
suitable diagram with source, foil, moveable detector
2 or more trajectories shown
vacuum
most particles have little if any deflection
large deflection of very few
reference to Coulomb’s law /elastic scattering
alphas repelled by nucleus (positive charges)
monoenergetic
OR electron scattering
High energy diagram with source sample, moveable detector / film
Vacuum
Electron accelerator or other detail
Most have zero deflection
Characteristic angular distribution with minimum
Minimum not zero
De Broglie wavelength
140
Describe the basic atomic structure of the atom and the relative sizes of the atom and the nucleus
Protons are in the nucleus they have a mass u and charge +e
Neutrons are also in the nucleus they do not have a charge and have a mass u
Electrons orbit the nucleus and have mass u/2000 and a charge -e
141
Describe how the strong nuclear force between nucleons is attractive and very short-ranged
Due to a strong force that binds quarks together to form neutrons and protons. Must be short range as it does not influence beyond the nuclear surface and strong enough to overcome the repulsive force of the protons.
142
Describe a simple quark model of hadrons in terms of up, down and strange quarks and their respective antiquarks, taking into account their charge, baryon number and strangeness.
There are three quarks with corresponding antiquarks. They have a fractional charge of either 1 or 2 thirds.
Baryons are made up of three quarks
Mesons are small and made of a quark and antiquark
143
Describe how the quark model may be extended to include the properties of charm topness and bottomness
3 more quarks called charmed, bottom and top.
Charmed quarks have a charge +2e/3 and a baryon number of 1/3
Bottom quarks have a charge of –e/3 and a baryon number of 1/3
Top quarks have a charge of +2e/3 and a baryon number of 1/3
144
Describe the properties of neutrons and protons in terms of a simple quark model
Neutrons- No charge, mass u, made of 1 up and 2 down quarks
Protons-+1 charge, mass u, made of 2 up and 1 down quark
145
Describe how there is weak interactions between quarks and that this is responsible for ß decay
Because of weak interactions between quarks a down quark is able to become an up quark turning a neutron into a proton and emitting an electron
146
Describe the two types of ß decay in terms of a simple quark model
β- decay a down quark turns into an up quark, this results in a neutron turning into a proton and emits an electron and an anti-electron neutrino (to conserve charge and lepton number)
β+ decay an up quark turns into a down quarkm, this meas that a proton turns into a neutron and a positron is emitted along with an electron neutrino
147
Describe the spontaneous and random nature of radioactive decay of unstable nuclei
Spontaneous: the decay cannot be induced / occurs without external influence
Random: cannot predict when / which (nucleus) will decay next
148
Describe the nature, penetration and range of α particles, ß particles and γ rays
Alpha particles are helium nuclei, have a charge +2e and cantravel through a few cm of air
## Footnote
Beta emissions are fast moving electrons, each has a charge of –e and can penetrate a few mm of aluminium
Gamma rays are electromagnetic radiation, as such they have no charge and penetrate a few cm of lead
149
Describe the use of radioactive isotopes in smoke alarms
Ionisation of air caused by a small alpha particle emitter with a long half-life, the alpha particles pass between electrodes producing a current. If there is more than a certain concentration of smoke alpha particles are absorbed and the current is then reduced, this then triggers the alarm
150
Describe the nature of x-rays
Composition of electric and magnetic fields which move perpendicular to each other
high energy, typically short wavelength and high frequency, highly penetrative.
151
Describe in simple terms how x-rays are produced
Firing high energy particles at a metal target results in collisions. These collisions are inelastic and some of the KE is transfered into X-ray radiation. The most powerful radiation is produced when the particles collide "head on" as this is where the largest loss of KE occurs.
152
Describe how x-rays interact with matter (limited to the photoelectric effect, Compton effect and pair production)
Some of the photons interact with the particles of the matter and their energy can be absorbed or scattered, others do not interact. The number of photons transmitted depends on thickness and density
153
Describe the use of x-rays in imaging internal body structures including the use of image intensifiers and of contrast media
Intensifier used as X-ray would pass through film
Intensifier converts X-ray photon to many visible (light) photons (which are absorbed by film)
Lower exposure / fewer X-rays needed
Iodine / barium (used as contrast material)
High Z number / large attenuation coefficient / large absorption coefficient (used to improve image contrast)
Contrast media are ingested / injected into the body
Absorption of X-rays by (silver halide molecules) by a photographic film
Uses of fluorescent / scintillator/ phosphor
Photon releases electron (that is accelerated onto a fluorescent screen)
number of electrons increased /multiplied
154
Describe the operation of a computerised axial topography (CAT) scanner
* The patient lies on table that moves in and out of a round opening known as the 'gantry'
* The ring inside the gantry contains a single X-ray tube and about 720 X-ray detectors.
* X-ray tube moves at high speed around the patient.
* X-rays pass through the patient and reach the detectors on the opposite side of the tube.
* Detectors monitor the intensity of the X-rays absorbed.
* The computer connected to the detectors records thousands of images or 'slices' through the patients.
* In a modern scanner, the X-ray tube can make three rotations every second and the computer can record 200 slices through the patient.
* A scan can take 10 to 30 minutes.
155
Describe the advantages of a CAT scan compared with an x-ray image
Differences: Simple X-ray is one directional / produces single image
Simple X-ray is one directional / produces single image
Computer processes data / image constructed from many slices
Advantages: X-ray image is 2D / CT scan produces 3D image
Greater detail / definition / contrast with CT scan / ‘soft tissues can be seen’
Image can be rotated
156
Describe the use of medical tracers like technetium-99m to diagnose the function of organs
Tracer administered will be giving off radiation so the path can be followed. It will not interfere with any functions of the body. And it must emit detectable radiation so that the image of the organs can be observed
157
Describe the main components of a gamma camera
Photon passed into a photomultiplier tube where it falls on a photocathode emitting an electron, which is accelerated towards a dynode. The dynode emits several electrons which are then accelerated and repeated multiple times and can then be amplified and processed
158
Describe the advantages and disadvantages of MRI
Advantage: not ionising radiation (as with X-rays) / better soft tissue contrast
Disadvantage: heating effect of metal objects /effect on cardiac pacemakers / takes a long time to perform MRI scan
method does not use ionising radiation
hence no radiation hazard to patient or staff
159
Describe the need for non invasive techniques in diagnosis
No surgery, less infections. Easy to monitor health with minimal harm to the body. Also allows more time to observe the body.
160
Describe the piezoelectric effect
The application of a p.d. across a material / crystal causes an expansion / contraction / vibration
161
Describe the principles of ultrasound scanning
Pulses of ultrasound (sent into the body)
Wave / ultrasound / pulse / signal is reflected (at boundary of tissue)
Time of delay used to determine depth / thickness
The fraction of reflected signal is used to identify the tissue
Small wavelength used which means finer detail can be seen / greater resolution
162
Describe the process of induced nuclear fission
The splitting of a heavy nucleus into two lighter nuclei of approximately the same mass
163
Describe the techniques of radioactive dating
Living plants / animals absorb carbon(-14)
Once dead, the plant does not take in any more carbon(-14)
The fraction of C-14 to C-12 (nuclei) or number of C-14 (nuclei) or activity of C-14 (nuclei) measured in dead and living (sample)
## Footnote
x = x0 e-(labda)t used with data above to estimate the age
164
Describe and explain the process of nuclear chain reaction
Occurs when one nuclear reaction causes an average of one of more nuclear reactions, thus leading to a self-propagating series of reactions
165
Describe the use of nuclear fission as an energy source
Advantages-does not produce acid rain or waste gases which cause pollution
-provides energy for nuclear power and can provide electricity
Disadvantages-problems with the reaction getting out of control
-risks from radiation
-long half life of waste
-can be used to drive nuclear weapons
166
Describe the peaceful and destructive uses of nuclear fission
Peaceful-Create Energy
Destructive-Nuclear Weapons
167
Describe the environmental effects of nuclear waste
Nuclear waste in water can contaminate wildlife, especially if it is still highly radioactive
168
Describe the process of nuclear fusion
Two or more atomic nuclei join together to form a single heavier nucleus, accompanied by the release of large quantities of energy
169
Outline Main principles of MRI scanning
Magnetic resonance:
some nuclei behave as small magnets / certain nuclei possess a net spin / nuclei line up in the magnetic field
Need for a strong magnetic field
the frequency of precession is known as Lamor frequency
Application of RF pulses
produces resonance / flip energy states
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RF pulse turned off nuclei relax / flip back (and emit RF signal)
RF detected (by coil receiver) and processed
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Use of non-uniform field / gradient field
To locate position of nuclei in body
QWC mark: difference in the relaxation times for hydrogen in different tissues / materials
