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
Fields and Their Consequences
Capacitor charge and discharge
- 7 things to know
- Papers 2 and 3
Overview
The time constant, the exponential equations, and the log-linear graphs used to find RC.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
How is the time constant defined, and why is it measured in seconds?
Numbers
How can the time constant be found graphically from a discharge curve?
Numbers
How do charge and potential difference vary with time during discharge?
Numbers
What do I₀ and RC represent in the discharge current equation?
Numbers
What happens to discharge current over time, and why does charging include (1 − e^(−t/RC))?
Numbers
What shape is a log-linear discharge plot, and how does its gradient give the time constant?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe how the charge on a capacitor changes with time when it is charged through a resistor.
Model answer
The charge increases from zero and asymptotically approaches a maximum value, following an exponential growth curve.
- 2
What shape of curve is produced when charge is plotted against time for a capacitor charging through a resistor?
Model answer
An exponential growth curve.
- 3
What shape of curve is produced when charge is plotted against time for a discharging capacitor?
Model answer
An exponential decay curve.
- 4
How does the potential difference across a capacitor change during charging?
Model answer
It increases exponentially from zero towards the supply voltage.
- 5
Describe how the current varies with time when a capacitor is being charged through a resistor.
Model answer
The current starts at a maximum value and decreases exponentially towards zero as the capacitor charges.
- 6
Why does the charging current decrease as a capacitor charges?
Model answer
As charge accumulates on the capacitor, the p.d. across it increases, reducing the p.d. across the resistor and hence reducing the current.
Other ways to work this
The same content, four other ways.
What is inside Levo
Six ways to work the same material.
Every question in Fields and Their Consequences, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
Or £46 a year, about £3.83 a month. Cancel anytime.