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
Electronics
Astables
- 4 things to know
- Paper 3, section B
Overview
The RC time constant, mark-to-space ratio and duty cycle, and varying the running frequency.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
What is the formula for an RC time constant, what happens to an astable's frequency if C is reduced, and what does the product RC give?
Numbers
What mark-to-space ratio gives a 50% duty cycle, and how is the frequency varied?
Process
What happens to the oscillation frequency of an astable if the resistance in the RC timing network is increased?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What type of circuit is an astable, and what does it produce without any external triggering?
Model answer
An astable is an oscillator circuit that continuously switches between two unstable states, producing a continuous square wave output without any external triggering.
- 2
Why is an astable described as having 'unstable' states?
Model answer
Because the circuit cannot remain permanently in either state; it automatically switches between the two states continuously.
- 3
What is the function of a clock pulse in digital circuits?
Model answer
A clock pulse is a regular, repeating digital signal used to synchronise operations in digital circuits.
- 4
What component provides the clock pulse for digital systems?
Model answer
An astable circuit provides the clock pulse.
- 5
Define clock rate (or pulse rate).
Model answer
Clock rate is the frequency of the clock signal, measured in hertz, representing the number of complete cycles per second.
- 6
What is the period of a clock pulse?
Model answer
The period is the time taken for one complete cycle of the clock pulse, measured in seconds.
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