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
Photons
- 9 subtopics
- 27 things to know
- AS Unit 2
What Photons covers
Photons is examined on AS Unit 2 of WJEC Physics, Electricity and Light. 115 recall questions across 9 subtopics.
The 9 subtopics
Each one has its own page.
- Photon energy and the electronvoltRecall questions on Photon energy and the electronvolt.Open →
- The photoelectric effectRecall questions on The photoelectric effect.Open →
- Stopping potential and the Planck constantRecall questions on Stopping potential and the Planck constant.Open →
- The photoelectric effect and photon energiesRecall questions on The photoelectric effect and photon energies.Open →
- Line spectra and energy levelsRecall questions on Line spectra and energy levels.Open →
- Demonstrating the photoelectric effectRecall questions on Demonstrating the photoelectric effect.Open →
- The electromagnetic spectrum and typical photon energiesRecall questions on The electromagnetic spectrum and typical photon energies.Open →
- Electron diffraction and the de Broglie relationshipRecall questions on Electron diffraction and the de Broglie relationship.Open →
- Radiation pressureRecall questions on Radiation pressure.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
In the equation E = hf, what does each symbol represent?
Key term
State the equation for photon energy in terms of wavelength.
Numbers
Light of frequency 5.63 × 10¹⁴ Hz falls on a metal of work function 2.20 eV. Calculate the maximum kinetic energy of the emitted electrons.
Key term
What determines the maximum kinetic energy of a photoelectron?
Key term
What happens to the diameter of the rings in an electron diffraction tube when the accelerating voltage is increased?
Key term
State the de Broglie relationship and define every symbol with its unit.
Key term
Explain how a solar sail can accelerate a spacecraft even though radiation pressure is so small.
Key term
What is wave-particle duality?
Key term
Define stopping potential in the context of the photoelectric effect.
Key term
State the equation relating maximum kinetic energy of photoelectrons to stopping potential.
Key term
State Einstein's photoelectric equation.
Key term
How is a line emission spectrum produced?
Key term
How is a line absorption spectrum produced?
Key term
Why must the zinc plate be freshly cleaned with emery paper before the photoelectric demonstration with a gold-leaf electroscope?
Key term
What is observed if the zinc plate photoelectric demonstration is repeated with the electroscope charged positively?
Key term
Which colour lies at the long-wavelength end of the visible spectrum, and at roughly what wavelength?
Key term
List the named regions of the electromagnetic spectrum in order of increasing wavelength.
Key term
Why does a beam of light exert a force on a surface it strikes?
Key term
What experimental evidence supports the particle nature of electromagnetic radiation?
Numbers
Calculate the maximum kinetic energy when elementary charge = 1.60 × 10⁻¹⁹ C, stopping potential = 7.4 V.
Key term
How does the photon picture explain the existence of a threshold frequency?
Key term
How does a line emission spectrum appear when viewed with a diffraction grating?
Key term
In the zinc plate photoelectric demonstration, what happens to the falling leaf if a sheet of glass is placed between the ultraviolet lamp and the plate?
Key term
State the orders of magnitude of the wavelengths of microwaves and of radio waves.
Key term
Describe the electron diffraction tube demonstration.
Key term
Why is the force on a perfect mirror twice the force on a perfectly black surface for the same incident beam?
Take Photons further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
The work function vs The threshold frequency
The work function: the least energy needed to release an electron from a metal surface. The threshold frequency: the lowest frequency of light that can release an electron at all.
A line emission spectrum vs Ionisation energy
A line emission spectrum: bright lines produced as electrons fall between energy levels. Ionisation energy: the energy needed to remove an electron from the atom altogether.
Questions from this topic
Each one with the model answer underneath.
- 1
What is a photon?
Model answer
A photon is a quantum (discrete packet) of electromagnetic radiation.
- 2
State the equation that relates the energy of a photon to its frequency.
Model answer
E = hf, where E is the photon energy, h is the Planck constant, and f is the frequency of the radiation.
- 3
In the equation E = hf, what does each symbol represent?
Model answer
E represents the photon energy, h represents the Planck constant, and f represents the frequency of the radiation.
- 4
Calculate the energy of a photon of frequency 6.63 × 10¹⁴ Hz, taking the Planck constant as 6.63 × 10⁻³⁴ J s.
Model answer
E = hf = 6.63 × 10⁻³⁴ × 6.63 × 10¹⁴, which is 4.40 × 10⁻¹⁹ J.
- 5
What is the approximate value of the Planck constant?
Model answer
h ≈ 6.63 × 10⁻³⁴ J s.
- 6
State the equation for photon energy in terms of wavelength.
Model answer
E = hc/λ, where h is the Planck constant, c is the speed of light, and λ is the wavelength.
What is inside Levo
Six ways to work the same material.
Photons revision questions
- What does Photons cover in WJEC A-Level Physics?
- 9 subtopics: photon energy and the electronvolt, the photoelectric effect, stopping potential and the planck constant, the photoelectric effect and photon energies, line spectra and energy levels, demonstrating the photoelectric effect, the electromagnetic spectrum and typical photon energies, electron diffraction and the de broglie relationship and radiation pressure. Each one has its own page with questions and model answers.
- How is Photons organised?
- By the WJEC 1420QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Photons, 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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