Key term
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
Thermal Physics
- 8 subtopics
- 24 things to know
- A2 Unit 3
What Thermal Physics covers
Thermal Physics is examined on A2 Unit 3 of WJEC Physics, Oscillations and Nuclei. 108 recall questions across 8 subtopics.
The 8 subtopics
Each one has its own page.
- Internal energy and heatRecall questions on Internal energy and heat.Open →
- Work, the first law and specific heat capacityRecall questions on Work, the first law and specific heat capacity.Open →
- Thermal equilibrium, temperature and absolute zeroRecall questions on Thermal equilibrium, temperature and absolute zero.Open →
- The internal energy of an ideal monatomic gasRecall questions on The internal energy of an ideal monatomic gas.Open →
- Work done by a gas at constant pressureRecall questions on Work done by a gas at constant pressure.Open →
- The p–V diagram and work as an areaRecall questions on The p–V diagram and work as an area.Open →
- Sign conventions and special cases of the first lawRecall questions on Sign conventions and special cases of the first law.Open →
- Measuring specific heat capacityRecall questions on Measuring specific heat capacity.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
How are negative values of Q, W and the internal energy change interpreted?
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State the internal energy of n moles of an ideal monatomic gas, defining each symbol.
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Why does a real gas have some molecular potential energy?
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Derive W = pΔV from the definition of work as force multiplied by distance.
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Explain in terms of the first law why the barrel of a bicycle pump becomes warm during rapid pumping.
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State the defining equation for specific heat capacity, with every symbol and unit.
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Describe the electrical method for finding the specific heat capacity of a metal block.
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Define the internal energy of a system.
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State the equation for the work done by a gas expanding at constant pressure.
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Explain why heat is described as energy in transit.
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In which direction does heat flow when two bodies at different temperatures are placed in contact?
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Explain why work, like heat, is described as energy in transit.
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State which quantity goes on each axis of a p–V diagram.
Process
A process on a p–V diagram runs from left to right. What does that tell you about the work?
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State the first law of thermodynamics as an equation, and define every symbol with its unit.
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What is absolute zero?
Numbers
A gas at a constant pressure of 1.0 × 10⁵ Pa expands by 2.5 × 10⁻³ m³. Calculate the work it does.
Key term
Is it correct to say that a hot object contains a large amount of heat?
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What is the internal energy of a system?
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State the equation for the work done by a gas expanding at constant pressure, and define each symbol with its unit.
Process
A process on a p–V diagram runs from right to left. What does that tell you about the work?
Key term
Apply the first law to the isothermal expansion of an ideal gas.
Key term
Define the specific heat capacity of a substance.
Take Thermal Physics further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Internal energy vs Heat
Internal energy: the sum of the potential and kinetic energies of all the molecules. Heat: energy in transit across a boundary because of a temperature difference.
Specific heat capacity vs Absolute zero
Specific heat capacity: the energy needed to raise one kilogram by one kelvin. Absolute zero: the temperature at which a system holds its least possible internal energy.
Questions from this topic
Each one with the model answer underneath.
- 1
Define the internal energy of a system.
Model answer
The sum of the potential and kinetic energies of all the molecules of the system.
- 2
What is absolute zero?
Model answer
The temperature of a system when it has minimum internal energy.
- 3
Why is the internal energy of an ideal monatomic gas wholly kinetic?
Model answer
The molecules of an ideal gas exert no forces on one another except during collisions, so they have no molecular potential energy.
- 4
State the equation for the internal energy of an ideal monatomic gas.
Model answer
U = (3/2)nRT, where n is the number of moles, R is the molar gas constant and T is the absolute temperature.
- 5
Calculate the internal energy of 2.0 mol of an ideal monatomic gas at 300 K, taking R as 8.31 J mol⁻¹ K⁻¹.
Model answer
U = 1.5 × 2.0 × 8.31 × 300 = 7.5 × 10³ J.
- 6
In which direction does heat flow across the boundary of a system?
Model answer
Heat enters a system whose temperature is lower than its surroundings and leaves one whose temperature is higher.
What is inside Levo
Six ways to work the same material.
Thermal Physics revision questions
- What does Thermal Physics cover in WJEC A-Level Physics?
- 8 subtopics: internal energy and heat, work, the first law and specific heat capacity, thermal equilibrium, temperature and absolute zero, the internal energy of an ideal monatomic gas, work done by a gas at constant pressure, the p–v diagram and work as an area, sign conventions and special cases of the first law and measuring specific heat capacity. Each one has its own page with questions and model answers.
- How is Thermal Physics organised?
- By the WJEC 1420QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Thermal Physics, 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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