Numbers
AQA A-Level Physics 7408
Measurements and Their Errors
Particles and Radiation
Topic overviewConstituents of the atomStable and unstable nucleiParticles, antiparticles and photonsParticle interactionsClassification of particlesQuarks and antiquarksApplications of conservation lawsThe photoelectric effectCollisions of electrons with atomsEnergy levels and photon emissionWave-particle duality
Waves
Mechanics and Materials
Electricity
Further Mechanics and Thermal Physics
Fields and Their Consequences
Topic overviewFieldsNewton's lawGravitational field strengthGravitational potentialOrbits of planets and satellitesCoulomb's lawElectric field strengthElectric potentialCapacitanceParallel plate capacitorEnergy stored by a capacitorCapacitor charge and dischargeMagnetic flux densityMoving charges in a magnetic fieldMagnetic flux and flux linkageElectromagnetic inductionAlternating currentsTransformers
Nuclear Physics
AstrophysicsOptional topic
Topic overviewAstronomical telescope consisting of two converging lensesReflecting telescopesSingle dish radio telescopes, I-R, U-V and X-ray telescopesAdvantages of large diameter telescopesClassification by luminosityAbsolute magnitude, MClassification by temperature, black-body radiationPrinciples of the use of stellar spectral classesThe Hertzsprung-Russell (HR) diagramSupernovae, neutron stars and black holesDoppler effectHubble's lawQuasarsDetection of exoplanets
Medical PhysicsOptional topic
Topic overviewPhysics of visionDefects of vision and their correction using lensesEar as a sound detection systemSensitivity and frequency responseDefects of hearingSimple ECG machines and the normal ECG waveformUltrasound imagingFibre optics and endoscopyMagnetic resonance (MR) scannerThe physics of diagnostic X-raysImage detection and enhancementAbsorption of X-raysCT scannerImaging techniquesHalf-lifeGamma cameraUse of high-energy X-raysUse of radioactive implantsImaging comparisons
Engineering PhysicsOptional topic
Turning Points in PhysicsOptional topic
Topic overviewCathode raysThermionic emission of electronsSpecific charge of the electronPrinciple of Millikan's determination of the electronic charge, eNewton's corpuscular theory of lightSignificance of Young's double slits experimentElectromagnetic wavesThe discovery of photoelectricityWave–particle dualityElectron microscopesThe Michelson-Morley experimentEinstein's theory of special relativityTime dilationLength contractionRelativistic mass and energy
ElectronicsOptional topic
Topic overviewMOSFET (metal-oxide semiconducting field-effect transistor)Zener diodePhotodiodeHall effect sensorDifference between analogue and digital signalsLC resonance filtersThe ideal operational amplifierInverting amplifier configurationNon-inverting amplifier configurationSumming amplifier configurationReal operational amplifiersCombinational logicSequential logicAstablesPrinciples of communication systemsTransmission mediaTime-division multiplexingAmplitude (AM) and frequency modulation (FM) techniques
Medical Physics
Absorption of X-rays
- 4 things to know
- Paper 3, section B
Overview
The exponential attenuation equation, the attenuation coefficients, and half-value thickness.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
What do the symbols in I = I₀e⁻μx mean, and how is the mass attenuation coefficient defined?
Numbers
What is half-value thickness, and how does it relate to the attenuation coefficient?
Key term
What is the physical basis for contrast in X-ray imaging?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How does X-ray intensity change as it passes through a material — linearly or exponentially?
Model answer
X-ray intensity decreases exponentially as it passes through a material, not linearly.
- 2
What does the linear attenuation coefficient μ represent physically?
Model answer
The linear attenuation coefficient μ represents the fraction of X-ray photons removed from the beam per unit thickness of material.
- 3
What is the unit of the linear attenuation coefficient μ?
Model answer
The unit is per metre (m⁻¹) or per centimetre (cm⁻¹).
- 4
State the exponential attenuation equation for X-rays passing through a material.
Model answer
I = I₀e⁻μx
- 5
In the X-ray attenuation equation I = I₀e⁻μx, what does the symbol I represent?
Model answer
I represents the transmitted intensity of the X-ray beam after passing through the material.
- 6
How is mass attenuation coefficient μₘ defined in terms of linear attenuation coefficient?
Model answer
Mass attenuation coefficient is defined as the linear attenuation coefficient divided by the density of the material: μₘ = μ/ρ
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