Numbers
OCR A-Level Physics A H556
Practical Skills in the Written Papers
The Practical Endorsement
Topic overviewAnalogue and digital measuring instrumentsImproving accuracy with repeat timing, fiducial markers and plumb linesTiming, calipers and micrometersConstructing and testing circuitsSignal generators and oscilloscopesGenerating and measuring wavesData loggers, modelling software and ionising radiation
Physical Quantities and Units
Making Measurements and Analysing Data
Nature of Quantities
Motion
Forces in Action
Work, Energy and Power
Materials
Newton’s Laws of Motion and Momentum
Charge and Current
Energy, Power and Resistance
Electrical Circuits
Waves
Topic overviewProgressive waves and their propertiesThe wave equationReflection, refraction and diffractionWave graphs and intensityThe electromagnetic spectrumPolarisationRefraction and refractive indexCritical angle and total internal reflectionThe principle of superpositionInterference, coherence and path differenceTwo-source interference, Young's double-slit experiment and the diffraction gratingForming stationary wavesStationary waves on strings and in air columnsMeasuring the speed of soundNode spacing, amplitude and phase in stationary wavesHarmonics and the fundamental mode
Quantum Physics
Thermal Physics
Topic overviewThermal equilibrium and absolute temperatureThe kinetic model of solids, liquids and gasesBrownian motion and internal energySpecific heat capacityMeasuring specific heat capacitySpecific latent heatMeasuring specific latent heatMoles, the Avogadro constant and kinetic theoryGas laws, the ideal gas equation and r.m.s. speedMaxwell-Boltzmann distribution, Boltzmann constant and internal energy
Oscillations
Gravitational Fields
Astrophysics and Cosmology
Topic overviewThe solar system and the birth of a starThe death of a low-mass starSupernovae, neutron stars and black holesThe Hertzsprung-Russell diagramEnergy levels and emission spectraAbsorption spectra and spectral linesPhoton energy and the diffraction gratingWien's law and Stefan's lawAstronomical distances, parallax and the cosmological principleDoppler shift and Hubble's lawThe expanding universe and the Big BangEvidence for the Big Bang and dark energy
Capacitors
Topic overviewCapacitance and charging a capacitorCapacitors in seriesCapacitors in parallel and combined circuitsEnergy stored by a capacitorCharging and discharging through a resistorInvestigating capacitor dischargeThe time constantIterative modelling, exponential decay and the constant-ratio property
Electric Fields
Electromagnetism
Nuclear and Particle Physics
Topic overviewAlpha-particle scattering and the nuclear modelProton number, nucleon number and isotopesThe strong nuclear force and nuclear radiusParticles, antiparticles and hadronsLeptons and the quark modelQuark composition and chargesBeta decay in the quark modelRadioactive decay and the three radiationsNuclear decay equationsActivity, decay constant and half-lifeExponential decay and radioactive datingMass-energy equivalenceAnnihilation, mass defect and binding energyBinding energy per nucleon and induced fissionThe fission reactor and nuclear wasteNuclear fusion and balancing nuclear equations
Capacitors
- 8 subtopics
- 24 things to know
- Papers 1, 2 and 3
What Capacitors covers
Storing charge and energy: capacitance, combining capacitors, the energy on a charged capacitor, and the exponential curve that governs charging and discharging.
Where it is assessed
Papers 1, 2 and 3
Newtonian world, astrophysics and particles, drawn on across the papers.
Check the OCR specification ↗The 8 subtopics
Each one has its own page.
- Capacitance and charging a capacitorRecall questions on capacitance, the farad and C = Q/V with calculations, and how electrons move onto and off the plates when a capacitor charges and discharges.Open →
- Capacitors in seriesRecall questions on total capacitance in series and calculations, charge and potential difference across series capacitors, and investigating capacitors in series with voltmeters and an ammeter.Open →
- Capacitors in parallel and combined circuitsRecall questions on total capacitance in parallel and calculations, potential difference and charge for parallel capacitors, Kirchhoff's laws in capacitor circuits, and investigating capacitors in parallel.Open →
- Energy stored by a capacitorRecall questions on the p.d.-charge graph, the three expressions for stored energy, and uses of capacitors as energy stores.Open →
- Charging and discharging through a resistorRecall questions on how charge, potential difference and current change as a capacitor charges and discharges through a resistor, the charging equation, and the ln(x) against t graph.Open →
- Investigating capacitor dischargeRecall questions on investigating capacitor discharge manually with a voltmeter and stopwatch or with a data-logger, and the linearised logarithmic form of the discharge equation.Open →
- The time constantRecall questions on the time constant CR with calculations, the fractions reached after one time constant during charging and discharging, the exponential discharge equation, and finding CR from a ln(x) against t graph.Open →
- Iterative modelling, exponential decay and the constant-ratio propertyRecall questions on the iterative equation ΔQ/Δt = −Q/CR, modelling capacitor discharge on a spreadsheet, why logarithms help analysis, and the shape and constant-ratio property of exponential decay.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
State the equation for the time constant of a capacitor-resistor circuit, and which quantities are multiplied to give it.
Numbers
State the exponential equation for capacitor discharge and what x₀ represents, and the fraction of its final value the charge or voltage reaches after one time constant of charging.
Key term
Define capacitance.
Numbers
State the equation relating capacitance, charge, and potential difference.
Numbers
State the formula for calculating the total capacitance of capacitors connected in series.
Numbers
For two capacitors in series, state the simplified formula for total capacitance.
Key term
What relationship should be verified when investigating capacitors in parallel?
Numbers
What is the gradient of a p.d.–charge graph for a capacitor?
Numbers
State the formula for energy stored by a capacitor in terms of charge and potential difference.
Numbers
How is the change in charge ΔQ calculated at each step in a spreadsheet model of discharge?
Key term
What is done after calculating the new charge value in spreadsheet modelling of discharge?
Key term
Express one farad in terms of base SI units of charge and potential difference.
Key term
During the charging of a capacitor through a resistor, where does the current flow from?
Key term
At the instant a fully charged capacitor begins to discharge, what can be said about the current?
Key term
What can be done with data collected by a data-logger after a capacitor experiment?
Key term
What is the SI unit of capacitance?
Numbers
Calculate the total capacitance when capacitors of 46 μF and 66 μF are connected in series.
Key term
For two capacitors in parallel, write the equation for total capacitance.
Key term
On a graph of p.d. against charge for a capacitor, what shape is produced and where does it pass through?
Key term
What happens to the charge on the plates of a capacitor as it charges through a resistor?
Key term
Explain why the current decreases during the discharge of a capacitor.
Key term
How does the recording method of a data-logger differ from manual measurements?
Key term
What is the first step when setting up a spreadsheet model for capacitor discharge?
Take Capacitors further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Capacitance vs Charge
Capacitance: the charge stored per unit potential difference. Charge: quantity of electricity held on capacitor plates.
Questions from this topic
Each one with the model answer underneath.
- 1
Define capacitance.
Model answer
Capacitance is the charge stored per unit potential difference across the capacitor.
- 2
What is the SI unit of capacitance?
Model answer
The farad (F).
- 3
State the formula used to calculate capacitance from charge and potential difference.
Model answer
C = Q/V, where C is capacitance, Q is charge, and V is potential difference.
- 4
What does the charge stored on a capacitor refer to, given that the capacitor as a whole has no net charge?
Model answer
The magnitude of the charge on either plate: one plate holds +Q and the other −Q.
- 5
In the equation C = Q/V, what does each symbol represent?
Model answer
C is capacitance (in farads), Q is charge stored (in coulombs), and V is potential difference across the capacitor (in volts).
- 6
Calculate the capacitance when charge = 0.0046 C, potential difference = 6 V.
Model answer
Capacitance = 0.0046 ÷ 6 = 0.000767 F.
What is inside Levo
Six ways to work the same material.
Capacitors revision questions
- What does Capacitors cover in OCR A-Level Physics A?
- 8 subtopics: capacitance and charging a capacitor, capacitors in series, capacitors in parallel and combined circuits, energy stored by a capacitor, charging and discharging through a resistor, investigating capacitor discharge, the time constant and iterative modelling, exponential decay and the constant-ratio property. Each one has its own page with questions and model answers.
- How is Capacitors organised?
- By the OCR H556 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Capacitors, 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.
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