Module 4 + 6 Model Answers Flashcards
(92 cards)
1
Q
Using Oscilloscope to measure Frequency
A
Oscilloscope to measure frequency
- Use sig. generator/tuning fork with mic and CRO
- Use loudest amplitude sound possible
- Adjust time base to get largest trace possible
- Adjust volts/div to get largest amplitude
- Multiply ms/div by number of divisions to get period - Frequency = 1/T
2
Q
Demonstrating/Explaining interference patterns
A
- Use appropriate detector to measure intensity/amplitude
- Maxima = highest intensity, constructive interference, in phase, path difference = nλ, Phase difference = even integer of π
- Minima = lowest intensity, destructive interference, in antiphase, path difference = (n+1/2)λ, Phase difference = odd integer of π
3
Q
I-V Characteristics PAG
A
- Set up circuit with variable resistor in series with component.
- Use variable resistor to change distribution of pd across circuit - record I at each setting.
- Plot graph of I against V
4
Q
Formation of standing waves (eg string, sound, microwaves)
A
- Incident wave reflects off end of string/surface
- Reflected wave superposes/interferes with incident wave
- Antinodes - where always constructive and Amplitude = MAX
- Nodes - where destructive and displacement always ZERO
5
Q
Finding Speed of sound from column of air
A
- Place tube vertically in bucket of water.
- Use signal generator to produce sound of known frequency and mic linked to CRO to detect
- Raise tube from 0 until Amplitude on CRO reaches max.
- This is first harmonic and so length is
- Multiple length by 4 to get
- Use c=3x10^8
6
Q
Describing example of PE effect
A
- Gold leaf electroscope - Charge it up and gold deflects.
- Shine normal light in Zn disc & gold leaf remains deflected regardless of time.
- Shine UV & g. leaf immediately returns loss of charge from Zn
7
Q
Explaining PE effect
A
- Electron emitted from surface of metal when light incident on surface
- Only occurs if frequencey > threshold frequency or if hf > work function of metal
- FTh in minimum f required to cause PE emission
- Work function is minimum energy required to remove photo electron from surface of metal.
- Rate of emission is proportional to Intensity (as long as if f > FTh)
8
Q
Evidence as particular nature of light
A
- Were light a wave light of any f would eventually cause PE emission
- Changing intensity has no effect on emission
9
Q
Conditions for interference with light
A
- Coherent sources (from a single monochromatic light split through slits),
- Narrow slits (to cause diffraction),
- Slits close together (so diffraction patterns can overlap),
- A distant screen (so the pattern is visible and measurable).
10
Q
Double slit method to measure wavelength and limitations
A
Measure D with ruler, fringes over several for accuracy.
Use micrometer for tiny slit separation.
Main issue: % uncertainty in fringe width — measure n fringes.
11
Q
Potential Dividers - Thermistor
A
- As T↓ R(thermistor)↑ so V(therm)↑ and V(fixed)↓
- To turn component ON as T↑ place across FIXED
- To turn component OFF as T↓ place across THERMISTOR
- Vice Versa for response to decreasing Temperature
12
Q
Potential Dividers - LDR
A
- As L↑ R(LDR)↓ so V(LDR)↓ and V(fixed) ↑
- To turn component ON as L↑ place across FIXED
- To turn component OFF as L↑ place across LDR
- Vice Versa for response to decreasing Light
13
Q
Describing and explaining interference patterns (eg walking past two speakers)
A
- Interference pattern is described by areas of Maxima and minima
- ·Maxima (loudest/brightest) - constructive interference - waves in phase - path difference 0 or any whole number of wavelengths nλ
- Minima (quietest/dullest) - destructive interference - waves in ANTIphase - Path difference = (n+1/2)λ
14
Q
Young’s double slit as evidence of wave nature of light
A
- Light passed through single slit - then to double slit to create coherent waves
- Double slit produced interference - we know that water waves interfere - therefore light must be wave
15
Q
Polarisation of Waves
A
- Can only occur with transverse waves
- Unpolarised wave has oscillations in all planes
- Polarising filter only allows through oscillations in direction of filter
16
Q
Proving a light wave is polarised (eg reflected off water)
A
- View wave through filter
- Rotate filter and observe change in intensity
- When filter is at 0 degrees to plane of polarisation I = max
- When filter is at 90 degrees to plane of polarisation I = 0
- When filter is at 180 degrees to plane of polarisation I = max
17
Q
Proving microwaves are polarised
A
- Use Microwave emitter and microwave receiver
- Either place grill/grating between and rotate OR
- Rotate receiver - Same as last 3 points above
18
Q
Plank Constant PAG + limitations
A
Method:
- Use a bank of LEDs (known wavelengths) with a flying lead and variable resistor
- Gradually increase voltage until each LED just begins to glow
- Record striking voltage V
- Plot graph of V against f
- Gradient = h/e so h = gradient x e
Limitation:
- External light makes LED appear to glow early → striking V too low → value of h too high
- Solution: View LEDs through a dark tube to reduce ambient light
19
Q
Describe and explain how the capacitor plates A and B acquire opposite charges when the switch is closed
A
Electrons in the circuit move in a clockwise direction and electrons are deposited on plate B. An equal number of electrons are removed from plate A giving it a positive charge of equal magnitude.
20
Q
State and explain what affects the time constant of a capacitor-resistor circuit.
A
- Double the resistance and time constant doubles and the rate of flow of charge halves.
- Double Capacitance doubles time constant as twice a much charge is needed for each volt increase or decrease.
21
Q
A student investigates the discharge of a capacitor.
Explain what graph they would plot to obtain a linear relationship and what key values can be obtained from the graph.
A
V=V₀eᵗ/ᶜᴿ
lnV=-t/CR
lnV=(-1/CR)t + lnV₀
Gradient (dy/dx)=-1/CR
so cr=-1/gradient.
22
Q
The capacitor consists of two parallel metal plates separated by air. The switch is closed to charge the capacitor. The switch is then opened and the separation between the charged plates is doubled. State and explain what happens to the energy stored by the capacitor.
A
The charge on each plate remains the same. C = ε0A/d, hence the capacitance is halved. E = ½ Q2/C, E ∝ 1/C and hence energy stored doubles.
23
Q
The capacitance of B is twice the capacitance of A. Explain why the potential difference across capacitor A is twice the potential difference across capacitor B.
A
The charge Q is the same on each capacitor is the same V = Q/C so V ∝ C⁻¹ hence CA is half CB so VA will be double VB
24
Q
Describe how a student could investigate how the voltage varies with time when a capacitor is discharged. PAG
A
- Choose values of C and R to give a time constant of about 2 minutes (Allows time to measure)
- Close switch to charge up capacitor. Measure initial p.d. and open the switch and recorded V and time every 20s for 5 minutes. Plot a graph of V against time. (or InV against t gradient = - CR)
25
Explain how you can prove that the data obtained for the voltage across a discharging capacitor against time is an exponential relationship using a Voltage time graph
* Plot a graph of Voltage against time.
* In exponential relationships the factor drops by the same ratio in equal time intervals.
* From the graph measure initial Vo and V1 after say 60s and calculate V1/Vo.
* Measure V2 after another 60s and calculate the ratio V2/V1.
* If the ratios are the same it is exponential decay
26
Define the time constant of a capacitor-resistor discharge circuit.
The time taken for the p.d / current / charge to decrease to 1/e (37%) of its initial value.
27
Describe how the time constant of this circuit can be determined experimentally in the laboratory.
Connect a voltmeter across the resistor (or capacitor) A stopwatch is started when the switch is opened and stopped when the p.d. decreases to 37% of its initial value. The time constant is the time taken for the p.d. to decreases to 37% of its initial value.
28
What is meant by exponential decay.
Factor drops by the same ratio in equal time intervals.
29
An electric field always exists around a charged particle. Explain what is meant by an electric field.
A region in which a charged particle experiences a force / acceleration.
30
Describe the similarities and the differences between the gravitational field of a point mass and the electric field of a point charge.
**Differences**
* gravitational field /force is attractive
* electric field / force can be either attractive or repulsive
**Similarities**
* Force / field (strength) inversely proportional to distance squared
* Radial fields
31
Describe some uses of capacitors as stores of energy
* Timing circuits
* Smoothing converted AC to DC
* Storing energy, e.g flash bulbs in a camera
32
Derive the equation for the capacitance of an isolated charged sphere
C=4πEoR
Using:
V=QC and V=Q/4πEor
33
A positively charged particle is travelling in a uniform field. at right angles to the direction of the field.
Describe the motion of the particle in terms of the force it experiences when the field is magnetic compared to electric
**For magnetic field**
* the motion is circular in the plane of paper
* Because the force is right angles to the motion / velocity.
**For electric field**
* particle moves to the right and either comes out or goes into the plane of the paper (in a parabolic path).
* Because particle experiences a force perpendicular to motion / velocity.
34
The figure shows two particles with the same charge but of opposite sign.
State and explain the magnitude of the electric potential at the midpoint between the particles.
* The magnitude of the electric potential is the same for both particles at the midpoint but of opposite sign.
* The total potential at the midpoint is zero.
35
Define electric potential at a point in space
Electric potential is the work done per unit charge in bringing a positive charge from infinity to the point.
36
Describe how a PET scanner is used to locate an area of increased activity within the patient
* The patient is surrounded by gamma detectors.
* Patient injected with tracer
* Increased activity where tracer accumulates
* Positrons emitted from tracer decay annihilate with electrons in patients body
* Each annihilation produces two gamma photons travelling in opposite directions
* Scanner detects gamma photons and arrival times are used to locate position of increased activity.
* Computer connected to detectors / gamma camera and an image is formed by the computer (using the electrical signals from the detectors).
37
Calculate the maximum photon wavelength that could create a pair production of an electron and a positron
* Remember what ever energies you are given in the question ignore!!!!!
* This is the minimum energy needed to create an electron positron pair without any extra KE, which will mean the photon has this minimum, thus the maximum wavelength possible.
* E = mc2 = 2mₑc2 (mₑ = mass of electron )
* E = hc/λ
38
What are the advantages and disadvantages of using CAT scans over traditional X-rays?
**Advantages**:
* CAT scans produce three-dimensional imaging.
* CAT scans can distinguish between soft tissues of similar attenuation coefficient
**Disadvantages**:
* CAT scans are more expensive and take longer than traditional x-ray
* The dosage for a CAT scan is much higher than the for a simple x-ray
* Patients need to remain very still during the scanning process.
39
Describe the process in using of CAT scans to form an image
* X-ray tube rotates around patient
* Fan shaped beam of X-rays
* Slice of X-ray image of patient produced
* Slices added together to create a 3D image
40
Describe and explain what contrast materials can be used in X-ray imaging and why they are needed.
* Soft tissues have low absorption coefficient, so contrast materials are used to improve visibility of internal structures in x-ray images.
* Barium and iodine are used as they have large atomic numbers, meaning attenuation coefficient is much higher than soft tissue.
* Barium sulphate is used in imaging of the digestive system.
* Iodine is used as contrast medium in liquids e.g. blood flow.
41
How does a gamma camera create an image from gamma radiation emitted by a radioactive tracer in the body?
* A radioactive tracer (gamma emitter) is injected into the patient.
* Gamma rays are emitted from the target organ as the tracer collects there.
* A collimator (lead grid) ensures only rays travelling straight through reach the detector.
* The rays hit a scintillator, which emits flashes of light.
* These are converted to electrical signals by photomultiplier tubes.
* A computer processes the signals to build a 2D image showing tracer distribution in the body.
42
Explain how an ultrasound transducer can emit ultrasound. and how it detects the received ultrasound
It uses the Piezoelectric effect
* An alternating p.d. is applied to the Piezoelectric crystal causing it to resonance (produce vibrations) which produces ultrasound.
* The reflected ultrasound causes the crystal to resonate, producing an alternating voltage.
43
During an ultrasound scan it is important that most of the ultrasound from the transducer is transmitted into the patient. Describe and explain how this is achieved.
* Gel is used (between transducer and skin).
* The acoustic impedance / Z of gel is similar to that for skin hence less reflection (at the skin)
44
Describe the basic structure of an X-ray tube and explain how X-ray photons are produced.
Electrons are produced in an evacuated tube by hot filament cathode (-)
They electrons are accelerated by a high voltage (supply) connected between cathode and metal anode target. The electrons hit the target metal anode and their KE is transformed into X-ray photons
45
PET scanners are not available in all hospitals. This is because fluorine-18 requires expensive on-site particle accelerators and fluorine-18 has a very small 'shelf-life'.
Discuss the ethical issues this raises in the treatment of patients.
Doctors have to make difficult decisions about who can and cannot have a PET scan. Some patients will miss out on PET scans because of their location / not all patients will have access to the scans.
46
Describe how ultrasound scanning is used to obtain diagnostic information about the internal structure of body. In your description include the difference between an A-scan and B-scan.
* Pulses of ultrasounds sent into the body, reflects of the boundary between tissues, due to a change in density.
* Time of delay used to determine depth/thickness
* The fraction of reflected signal is used to identify the tissue.
* A scan is in one direction only
* B-scan uses a number of senses in different positions producing 2D or 3D images
47
Explain a method using ultrasound to determine the speed of blood in an artery in the arm
Pulses of ultrasound waves reflected from the moving blood cells in the artery.
The transducer is placed at an angle (usually 600)
The frequency of reflected waves is different to that of the emitted waves.
The ratio of the frequencies enables the speed of blood flow to be calculated
48
Describe and explain a technique that can be used for revealing blood vessels in x-rays
Iodine is injected into the blood as a contrast material.
It has a high absorption coefficient, because of its large atomic size (Z is high)
49
Briefly describe the function of the collimator, scintillator and photomultiplier tubes in a gamma camera.
* **Collimator**: Is made of long and thin tubes so only gamma photons travel along the axes of lead tubes are detected. This produces a sharper image of the patient
* **Scintillator**: Each gamma photon produces thousands of photons of visible light.
* **Photomultiplier**: An electrical pulse is produced from each photon of visible light entering a photomultiplier tube.
50
Explain how the reflection of ultrasound at a boundary between two tissues depends on the physical properties of the tissues.
* Refection is caused when there is a change in acoustic impedance Z, between two tissues. (Z = )
* Same impedance results in no reflection,
* The greater the difference in impedance the greater the reflected intensity.
* Ir/I0 = [Z1 - Z2]2/[Z1 + Z2]2
51
Define the acoustic impedance of a material and give the SI unit
acoustic impedance = speed (of ultrasound in the material) × density (of material)
kg m⁻² s⁻¹
52
Explain what is meant by the piezoelectric effect.
Applying a p.d across the material makes it expand / compress / deform / strain
53
Explain what is meant by Doppler effect.
Change in the frequency / wavelength because of source / 'observer' moving
54
State, with a reason, whether or not protons and neutrons are fundamental particles.
They are not fundamental particles because they consist of quarks
55
Explain how the experiments on the scattering of alpha-particles by a metal foil provided evidence for the nuclear model of the atom
* Most of the alpha particles went straight through showedthat most of the atom is empty space
* Some of the alpha particles were scattered through small angles showing a positive nucleus
* Very few of the alpha particles were scattered through large angles showed the existence of small / dense
56
State the quark composition of a proton and neutron
Neutron - u d d
Proton - u u d
57
Describe the nature of the strong nuclear force
It acts between quarks / nucleons / hadrons 'Short-range' force Repulsive below about 0.5 fm Attractive up to about 3 fm
58
State two fundamental particles that can be classified as leptons.
Any two from: electron / positron / neutrino / antineutrino
59
The alpha-particle comes to rest instantaneously a short distance away from a gold nucleus. It then reverses its direction of travel, to the left. Describe and explain the motion of the gold nucleus at the instant the alpha-particle is at rest
The gold nucleus has velocity / accelerates / moves to the right. There is a repulsive force on the gold nucleus. According to conservation of momentum the gold nucleus must move to the right
60
What is the definition of a Hadron
A Particle or antiparticle that is affected by the strong nuclear force, e.g. a proton.
61
What is the definition of a Lepton
A fundamental particle or anti particle that is not affected by the strong force, e.g. an electron
62
What type of nucleus decays beta minus emission? and describe what happens in beta minus decay
* An unstable nucleus which is neutron heavy (rich) decays by beta minus emission.
* A neutron decays into a proton, an electron and an electron antineutrino.
63
Explain why the mean density of all nuclei is about the same.
Density = mass/volume
Mass ∝ A
Volume ∝ r³ ∝ A¹/³ ∝ A
Therefore ∝ A/A or constant
64
What are the similarities and differences between mesons and baryons?
Both are hadrons, baryons are made up of three quarks, mesons are made up of a quark and an antiquark.
65
What type of nucleus decays beta plus emission? and describe what happens in beta minus decay.
An unstable nucleus which is proton heavy (rich) decays by beta plus emission.
A proton decays into a neutron, a positron and an electron neutrino.
66
Explain why the total mass of the individual nucleons of a nucleus is different from the mass of the nucleus.
Energy must be supplied to remove the nucleons from the nucleus, so the mass of the nucleons increases.
(Δ)E = (Δ)mc2 and (Δ)E is the (binding) energy and (Δ)m is the mass defect or the difference in mass.
67
Energy in the core of a nuclear reactor is produced by induced nuclear fission of uranium-235 nuclei. Explain what is meant by induced nuclear fission.
A (thermal / slow-moving) neutron splits the nucleus into two (smaller) nuclei and (fast-moving) neutron(s)
68
Explain the purpose of using control rods in the core of a nuclear reactor.
The control rods absorb some of the neutrons.
So one neutron survives between successive fission reactions.
69
Explain what is meant by the binding energy of a nucleus
The helium nucleus has greater charge so the nucleus experiences a greater repulsive force Helium nuclei need to get close together for the strong force to initiate fusion, so need to be moving faster, hence the higher temperature.
70
A neutron inside a nucleus is stable. However, a 'free' neutron, when outside the nucleus, undergoes beta decay with a half-life of about 11 minutes.
Explain what is meant by the half-life of a free neutron.
(Average) time taken for half of the neutrons (in a sample) to decay.(Average) time taken for half of the neutrons (in a sample) to decay.
71
Explain the purpose of using a moderator in the core of a nuclear reactor.
* Fission reactions produce fast neutrons.
* The moderator slows down the fast-moving neutrons as the neutrons collide with the moderator nuclei and transfer some of their kinetic energy.
* Slow-moving neutrons have a greater chance of causing fission reactions
72
Explain why energy is released in any nuclear reaction (This applies to any nuclear equation you are given!!!)
There is a decrease in mass
Energy released given by ΔE = Δmc²
73
Explain why fusion of helium requires higher temperatures than the fusion of hydrogen (protons)
The helium nucleus has greater charge so the nucleus experiences a greater repulsive force Helium nuclei need to get close together for the strong force to initiate fusion, so need to be moving faster, hence the higher temperature
74
State what is meant by the decay constant of an isotope.
The decay constant is the probability of decay of a nucleus per unit time.
75
What different conditions are required for nuclear fission and fusion to occur in a sustained manner?
* **Fission**: Sustained fission requires controlling the chain reaction by absorbing or slowing released neutrons (using control rods or moderators) to keep the reaction steady in a reactor.
* **Fusion**: Sustained fusion needs a very high temperature, high density, and sufficient plasma so that nuclei collide frequently enough to fuse—conditions found in stars like the Sun.
76
Explain why the method of carbon dating is not appropriate for samples that are greater than 105years old
Activity so low that it cannot be differentiated from the background
77
Describe the processes of fission and fusion of nuclei stating one similarity and one difference between the two processes
**fission**: slow moving neutron is absorbed by the nucleus causing it to split into two smaller nuclei and several neutrons
**fusion**: two light nuclei moving rapidly enough overcome the electrostatic repulsion between them to fuse.
**similarity (S)**
1. release of energy
2. total (rest) mass decrease
3. 'increase' in binding energy
4. conservation of charge / mass-energy.
**difference (D)**
1. Fission cold, fusion hot
2. Fission involves heavy nuclei, fusion light nuclei
3. Fission releases a large amount of energy release per reactioncompared to fusion
78
State one major disadvantage of having fission reactors.
Fission reactors produce radioactive by-products which affect future generations and the environment in terms of possible contamination / exposure to humans and animals.
79
Energy is released in both fission and fusion reactions. Describe two differences between fission and fusion reactions
* A nucleus is split up in a fission reaction. In a fusion reaction nuclei are fused
* High temperatures are required for fusion reaction
* More energy per reaction produced in a fission reaction
* A neutron causes fission reaction
* Chain reaction possible in fission
* 'Larger' nuclei produced in fusion, Smaller' nuclei produced in fission
80
Describe an experiment in order to investigate the absorption coefficient of lead for gamma radiation and to determine the half-thickness for lead
* Measure background radiation over a 60 seconds and calculate background count rate
* Set the GM tube at a distance from the gamma source which is just larger than the total thickness of the lead used.
* Measure the count-rate for different thicknesses of lead and subtract background count rate
81
Fusion reactions between hydrogen nuclei occur inside stars. Explain why very high temperatures and high pressures within stellar cores are necessary for fusion.
* There is electrostatic repulsion between nuclei
* At high temperatures nuclei move fast / have more KE So the nuclei have greater chance of fusion.
* As nuclei get close enough to experience the strong force
82
Plan one or more experiments to determine the nature of the emissions from a rock sample that contains several different radioactive elements.
* Range or absorption experiment suggested
* Suitable arrangement and choice of apparatus e.g. on diagram; allow GM tube as detector for all particles.
* Description of range or penetration experiment: α place detector very close less than 1cm from source; measure count rate, use paper screen, measure count rate, interpret result; contrast to background count level and/or other emissions from same source β place detector e.g. 10 cm from source measure count rate, add thin sheets of Al until count drops to very low or almost constant value e.g. γ present; interpret result; γ place detector e.g. 10 cm from source measure count rate, add thin sheets of Pb until count drops to very low/background level; interpret result
83
A protactinium generator can be used in a lab to investigate half-life. When shaken it produces protactinium, a beta emitter with a half-life of about 70 seconds.
Describe how you collect data to determine the half-life of protactinium, what graph you would plot and how you would obtain a value for the half-life
Measure background count for 60 seconds and calculate background count per second.
Shake protactinium generator to produce protactinium.
Place GM tube very close to the top of the generator bottle
Measure the counts rate every 20 seconds for 5 minutes
Subtract the background count rate from each reading
Plot a graph of InC against time (C = count rate)
Gradient = -λ
Half life = (ln2)/λ
84
Describe the method of carbon dating technique for dating a piece of wood (e.g an axe handle) and explain one of its major limitations
* Living things take in carbon (dioxide), which stops after death.
* The ratio of carbon-14 to carbon -12 drops over time as carbon-14 decays.
* The count rate from the decay of carbon-14 for a sample of the axe is measured.
* The count rate from the decay of carbon-14 in the same mass of a living sample of wood is determined.
* The age of the relic is found using 'A = A0e-λt'.
**Limitations**: The ratio of carbon-14 to carbon-12 is assumed to be that same now as in the past. Count ratefrom relic may be comparable to background count rate.
85
The fusion of two 3/1Hnuclei produces a stable nucleus of 4/2He and some fast-moving neutrons.
Explain why the fusion of the 3/1H nuclei must produce two neutrons
total nucleon number after fusion = 3 + 3 − 4 = 2
total proton number after fusion = 1 +1 − 2 = 0
Hence it must be 2 neutrons after the fusion reaction
86
Describe what is meant by chain reaction in a fission reaction
More neutrons produced (from each fission reaction) Go on to produce further (fission) reactions / splitting (of nuclei) / energy
87
Describe an experiment in order to investigate the inverse square law of gamma radiation.
* Measure background count for 60 seconds and calculate background count rate
* Set up the gamma source and GM tube 5cm apart.
* Record the Count rate using a GM tube and Counter and subtract background count.
* Repeat for distances of 10, 15, 20, 25, 30, 35, 40, 45 and 50cm
* Plot a graph of Count rate against distance
* The graph should be a straight line through the origin, proving the inverse square law
88
Describe what is meant by 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.
89
Explain the process of simple scattering
* X-rays of energy between 1 and 20keV are directed at a material
* The X-rays will reflect off layers of atoms or molecules in the material because they have insufficient energy to undergo more complex processes (like the photoelectric effect)
90
Explain the process of the photoelectric effect.
* X-rays of energy less than 100keV are directed at a material
* The X-rays can be absorbed by electrons in the material if they have the same energy as the ionisation energy of the atoms
* When an X-ray is absorbed, a photoelectron is released and another electron may de-excite, releasing another photon in the process
91
Explain the process of the Compton Effect.
* X-rays of energy between 0.5 and 5MeV are directed at a material
* The X-rays will lose a small amount of their energy to electrons in the absorbing materials due to an inelastic collision between the photon and electron.
* The scattered X-ray photon will have less energy than before (greater wavelength)
* The Compton electron will be scattered in a different direction as momentum must be conserved.
92
Explain the process of pair production.
An X-ray of energy greater than 1.02MeV passes through the electric field of an atom
An electron-positron pair is produced
The positron will annihilate with another electron and produce two photons
This process is not very important in medical X-rays as the photon energies are usually not high enough to cause pair production.
