Numbers
WJEC A-Level Physics 1420QS
Basic Physics
Kinematics
Dynamics
Energy Concepts
Solids Under Stress
Using Radiation to Investigate Stars
Particles and Nuclear Structure
Topic overviewQuarks, leptons and hadronsThe four interactions and conservation lawsThe first generation of quarks and leptonsAntiparticles and annihilationBaryons, antibaryons and mesonsDeducing quark compositions from chargeBeta decay and quark flavour changeTesting a reaction against the conservation rules
Conduction of Electricity
Resistance
Topic overviewCalculating resistance from resistivityPotential difference, Ohm's law and powerResistivity, temperature and superconductivityThe volt: energy transferred per unit chargeCurrent–voltage characteristics of non-ohmic componentsMeasuring resistance and resistivity in the laboratoryThe heating effect of a current and choosing a power equationThermistors and how a semiconductor's resistance falls with temperatureConductance, conductivity and comparing materials
D.C. Circuits
Topic overviewKirchhoff's laws, and resistors in series and parallelPotential dividers, emf and internal resistanceCells, resistivity, power and energyWorking out currents and potential differences in resistor networksSensor circuits with thermistors and LDRsInternal resistance, power transfer and short-circuit currentAmmeters, voltmeters and their effect on the circuit
The Nature of Waves
Wave Properties
Topic overviewEnergy transfer and the wave equationTransverse and longitudinal waves, path difference and intensityDiffraction and superpositionTwo-source interference and the diffraction gratingStationary wavesHow much a wave spreads at a gap or an obstacleCoherence and the conditions for observable interferenceYoung's double slit and λ = ay/DMeasuring wavelength with a diffraction gratingMeasuring the speed of sound with stationary waves
Refraction of Light
Photons
Topic overviewPhoton energy and the electronvoltThe photoelectric effectStopping potential and the Planck constantThe photoelectric effect and photon energiesLine spectra and energy levelsDemonstrating the photoelectric effectThe electromagnetic spectrum and typical photon energiesElectron diffraction and the de Broglie relationshipRadiation pressure
Lasers
Circular Motion
Vibrations
Topic overviewSimple harmonic motion and its equationsOscillating systems and energyDamping and resonanceThe simple pendulumThe mass–spring oscillatorThe displacement and velocity equationsGraphs of displacement, velocity and accelerationThe energy interchange in simple harmonic motionFree and forced oscillationsLight, heavy and critical damping
Kinetic Theory
Thermal Physics
Topic overviewInternal energy and heatWork, the first law and specific heat capacityThermal equilibrium, temperature and absolute zeroThe internal energy of an ideal monatomic gasWork done by a gas at constant pressureThe p–V diagram and work as an areaSign conventions and special cases of the first lawMeasuring specific heat capacity
Nuclear Decay
Nuclear Energy
Capacitance
Topic overviewCapacitance and the parallel plate capacitorEnergy, combinations and RC circuitsCharging at constant current and measuring capacitanceDielectrics and relative permittivityThe uniform field between capacitor platesEnergy stored in a capacitor and the Q–V graphExponential discharge, the time constant and log graphsCapacitors in series and parallel: charge and potential difference sharing
Electrostatic and Gravitational Fields of Force
Topic overviewElectric and gravitational fields comparedField lines, equipotentials and combining fieldsElectric potential and the work done on a chargeGravitational potential and potential energyAdding potentials and fields from several sourcesEquipotential surfacesComparing the two fields point by point
Orbits and the Wider Universe
Topic overviewKepler's laws and orbital motionThe Doppler effect, dark matter and the expanding universeNewton's law of gravitation applied to orbitsDeriving Kepler's third lawFinding the mass of a central objectGalactic rotation curves and dark matterThe centre of mass of a two-body systemRadial velocity and the Doppler shift of spectral linesHubble's law and the age of the universe
Magnetic Fields
Topic overviewMagnetic fields and field patternsMagnetic flux density and the force on a conductorThe force on a moving charge and its circular pathThe Hall effect and the Hall voltageMagnetic fields due to a current in a wire and in a solenoidForces between current-carrying conductorsCharged particle beams, velocity selectors and accelerators
Electromagnetic Induction
Option A: Alternating CurrentsOption A
Option B: Medical PhysicsOption B
Topic overviewMedical physicsUltrasound imagingRadiation and living tissueX-ray production and beam controlAttenuation and half-value thicknessRadiography, fluoroscopy and CT scanningAcoustic impedance and ultrasound reflectionMagnetic resonance imagingAbsorbed dose, equivalent dose and effective doseRadionuclide tracers, the gamma camera and PET
Option C: The Physics of SportsOption C
Topic overviewCentre of gravity, stability and momentsRestitution, moment of inertia and angular momentumRotational energy, projectiles and the flight of a ballMoments in the muscles and jointsApplying the impulse equation in sportMoment of inertia and angular kinematicsTorque, angular momentum and its conservationRotational energy and energy conservation in sport
Option D: Energy and the EnvironmentOption D
Topic overviewFactors affecting the rate at which the temperature of the Earth risesThe Earth's thermal equilibrium, Wien's law and Stefan's lawRenewable and non-renewable sourcesSolar energy and photovoltaic cellsWind, tidal and hydroelectric powerNuclear fission and fusion as energy sourcesU-values and rates of heat lossFuel cells and how they workFuel cells: benefits, limitations and the hydrogen economyThermal conduction, conductivity and insulation
Mathematical Requirements (Appendix C)
Topic overviewSignificant figures and arithmetic meansUncertainty and how uncertainties combineAlgebraic symbols and proportionalityRearranging and solving equationsSmall angle approximationsTangents and instantaneous rates of changeAreas under curves and numerical methodsReading a tangent on a motion graphStraight-line graphs and y = mx + cWhat a gradient and an intercept representLinearising a relationship to find a constantLog plots of exponential decayChoosing what to plot to find a constantLogarithmic scales and orders of magnitudeWorking with base-ten logarithmsThe shapes of common graphsInverse and root relationships on a graphAreas, volumes and PythagorasGeometry applied to physical situationsSubstituting into physical equationsTrigonometry and right-angled trianglesResolving a force into componentsRadians, arc length and force diagramsRandom processes and translating between representationsMean values and periodic functionsSymbols for approximation and comparison
D.C. Circuits
- 7 subtopics
- 20 things to know
- AS Unit 2
What D.C. Circuits covers
D.C. Circuits is examined on AS Unit 2 of WJEC Physics, Electricity and Light. 107 recall questions across 7 subtopics.
The 7 subtopics
Each one has its own page.
- Kirchhoff's laws, and resistors in series and parallelRecall questions on Kirchhoff's laws, and resistors in series and parallel.Open →
- Potential dividers, emf and internal resistanceRecall questions on Potential dividers, emf and internal resistance.Open →
- Cells, resistivity, power and energyRecall questions on Cells, resistivity, power and energy.Open →
- Working out currents and potential differences in resistor networksRecall questions on Working out currents and potential differences in resistor networks.Open →
- Sensor circuits with thermistors and LDRsRecall questions on Sensor circuits with thermistors and LDRs.Open →
- Internal resistance, power transfer and short-circuit currentRecall questions on Internal resistance, power transfer and short-circuit current.Open →
- Ammeters, voltmeters and their effect on the circuitRecall questions on Ammeters, voltmeters and their effect on the circuit.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
State three formulae that can be used to calculate power dissipated in a resistor.
Key term
What does Kirchhoff's first law state about currents entering a junction?
Key term
What fundamental principle underlies Kirchhoff's first law?
Key term
What is a potential divider?
Numbers
State the formula for the output voltage of a potential divider.
Numbers
Calculate the combined resistance of a 30 Ω resistor and a 60 Ω resistor connected in parallel.
Key term
What happens to the total resistance of a network when a further resistor is connected in parallel with part of it?
Key term
Describe the arrangement of a potential divider used as a temperature sensor.
Key term
How would a temperature-sensing divider be rearranged so that its output falls as the temperature rises?
Key term
Explain why a car's headlamps dim while the starter motor is being operated.
Numbers
A cell of electromotive force 1.5 V has an internal resistance of 0.30 Ω. Calculate the current if its terminals are short-circuited.
Key term
How is an ammeter connected into a circuit, and why must it be connected that way?
Key term
What is the resistance of an ideal ammeter, and why?
Who and when
According to Kirchhoff's second law, what is the relationship between EMFs in a closed loop?
Key term
What determines the output voltage in a potential divider circuit?
Key term
When cells are connected in series, how is the total EMF calculated?
Key term
In a divider containing a light-dependent resistor and a fixed resistor, how can the output be made to rise as it gets darker?
Key term
Why does a high-resistance voltmeter connected across an unloaded cell read very nearly its electromotive force?
Key term
How is a voltmeter connected into a circuit?
Take D.C. Circuits further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Resistance vs Resistivity
Resistance: the potential difference across a component divided by the current through it. Resistivity: a property of the material, relating a conductor's opposition to its length and cross-sectional area.
Electromotive force vs Terminal potential difference
Electromotive force: the energy given to each coulomb of charge by the source. Terminal potential difference: the energy delivered to the external circuit by each coulomb.
A series circuit vs A parallel circuit
A series circuit: one in which the same current passes through every component. A parallel circuit: one in which the same potential difference is across every branch.
Questions from this topic
Each one with the model answer underneath.
- 1
What does Kirchhoff's first law state about currents entering a junction?
Model answer
The sum of currents entering a junction equals the sum of currents leaving it.
- 2
What fundamental principle underlies Kirchhoff's first law?
Model answer
Conservation of charge.
- 3
Why must the total current entering a junction equal the total current leaving it?
Model answer
Because charge is conserved and cannot accumulate at a junction.
- 4
According to Kirchhoff's second law, what is the relationship between EMFs in a closed loop?
Model answer
The sum of electromotive forces in any closed loop equals the sum of potential differences across components in that loop.
- 5
In Kirchhoff's second law, what must the sum of EMFs equal?
Model answer
The sum of potential differences across all components in the closed loop.
- 6
To what type of path does Kirchhoff's second law apply?
Model answer
A closed loop in a circuit.
What is inside Levo
Six ways to work the same material.
D.C. Circuits revision questions
- What does D.C. Circuits cover in WJEC A-Level Physics?
- 7 subtopics: kirchhoff's laws, and resistors in series and parallel, potential dividers, emf and internal resistance, cells, resistivity, power and energy, working out currents and potential differences in resistor networks, sensor circuits with thermistors and ldrs, internal resistance, power transfer and short-circuit current and ammeters, voltmeters and their effect on the circuit. Each one has its own page with questions and model answers.
- How is D.C. Circuits organised?
- By the WJEC 1420QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in D.C. Circuits, 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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