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
Resistance
- 9 subtopics
- 27 things to know
- AS Unit 2
What Resistance covers
Resistance is examined on AS Unit 2 of WJEC Physics, Electricity and Light. 127 recall questions across 9 subtopics.
The 9 subtopics
Each one has its own page.
- Calculating resistance from resistivityRecall questions on Calculating resistance from resistivity.Open →
- Potential difference, Ohm's law and powerRecall questions on Potential difference, Ohm's law and power.Open →
- Resistivity, temperature and superconductivityRecall questions on Resistivity, temperature and superconductivity.Open →
- The volt: energy transferred per unit chargeRecall questions on The volt: energy transferred per unit charge.Open →
- Current–voltage characteristics of non-ohmic componentsRecall questions on Current–voltage characteristics of non-ohmic components.Open →
- Measuring resistance and resistivity in the laboratoryRecall questions on Measuring resistance and resistivity in the laboratory.Open →
- The heating effect of a current and choosing a power equationRecall questions on The heating effect of a current and choosing a power equation.Open →
- Thermistors and how a semiconductor's resistance falls with temperatureRecall questions on Thermistors and how a semiconductor's resistance falls with temperature.Open →
- Conductance, conductivity and comparing materialsRecall questions on Conductance, conductivity and comparing materials.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State three equivalent equations for the power dissipated in a resistor.
Key term
State the equation that defines potential difference in terms of energy and charge, and define every symbol with its unit.
Key term
Describe the current–voltage characteristic of a semiconductor diode when it is reverse biased.
Key term
Why is a graph of many readings better than a single pair of measurements for finding resistivity?
Key term
Why should the current through the wire be kept small and switched off between readings?
Key term
Why is a micrometer needed for the diameter of the wire while a metre rule is good enough for its length?
Key term
Why does a metal behave in the opposite way to a semiconductor when both are heated?
Key term
Why is conductance a more convenient quantity than resistance for a parallel combination?
Key term
Why is copper used for connecting leads but nichrome for the element of an electric fire?
Key term
In the formula R = ρL/A, what does R represent and what is its unit?
Key term
Define potential difference between two points in a circuit.
Key term
State the equation relating resistance to resistivity.
Key term
What is the SI unit of resistivity?
Key term
Express the volt in SI base units.
Key term
Why is a rheostat connected in series less satisfactory than a potential divider when a characteristic is being obtained?
Key term
Which power equation is the convenient one to use for components carrying the same current, and why?
Key term
Which power equation is the convenient one for components connected across the same potential difference, and why?
Key term
Describe the shape of a graph of resistance against temperature for an NTC thermistor.
Key term
After measuring the diameter of a circular wire, how do you obtain the radius?
Key term
In what unit is potential difference measured, and what is that unit equivalent to?
Numbers
Calculate the resistance of a copper wire 2.5 m long of cross-sectional area 1.5 × 10⁻⁶ m², taking ρ as 1.7 × 10⁻⁸ Ω m.
Numbers
A 9.0 V battery drives a current of 0.40 A for 2.0 minutes. Calculate the energy it delivers.
Key term
Why must a resistor be connected in series with a diode that is forward biased?
Key term
In a series circuit containing two unequal resistors, which one dissipates the greater power?
Key term
Why must the current passed through a thermistor be kept small when its resistance is being investigated?
Numbers
Calculate the conductance of a 250 Ω resistor.
Take Resistance further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Superconductivity vs The transition temperature
Superconductivity: the complete loss of electrical resistivity below a certain temperature. The transition temperature: the temperature at which that loss occurs.
Questions from this topic
Each one with the model answer underneath.
- 1
In the formula R = ρL/A, what does R represent and what is its unit?
Model answer
R represents resistance, measured in ohms (Ω).
- 2
State the formula used to calculate the resistance of a conductor from its physical dimensions and material property.
Model answer
R = ρL/A, where ρ is resistivity, L is length, and A is cross-sectional area.
- 3
After measuring the diameter of a circular wire, how do you obtain the radius?
Model answer
Calculate the radius by halving the diameter (r = d/2).
- 4
How is the cross-sectional area calculated for a conductor with a rectangular cross-section?
Model answer
A = width × height.
- 5
Calculate the cross-sectional area when width = 0.001 m, height = 0.032 m.
Model answer
Cross-sectional area = 0.001 × 0.032 = 0.000032 m².
- 6
Why is resistivity considered a material property rather than a property of a specific conductor?
Model answer
Because resistivity depends only on the material itself and is independent of the conductor's length or cross-sectional area.
What is inside Levo
Six ways to work the same material.
Resistance revision questions
- What does Resistance cover in WJEC A-Level Physics?
- 9 subtopics: calculating resistance from resistivity, potential difference, ohm's law and power, resistivity, temperature and superconductivity, the volt: energy transferred per unit charge, current–voltage characteristics of non-ohmic components, measuring resistance and resistivity in the laboratory, the heating effect of a current and choosing a power equation, thermistors and how a semiconductor's resistance falls with temperature and conductance, conductivity and comparing materials. Each one has its own page with questions and model answers.
- How is Resistance organised?
- By the WJEC 1420QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Resistance, 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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