Key term
AQA A-Level Physics 7408
Measurements and Their Errors
Particles and Radiation
Topic overviewConstituents of the atomStable and unstable nucleiParticles, antiparticles and photonsParticle interactionsClassification of particlesQuarks and antiquarksApplications of conservation lawsThe photoelectric effectCollisions of electrons with atomsEnergy levels and photon emissionWave-particle duality
Waves
Mechanics and Materials
Electricity
Further Mechanics and Thermal Physics
Fields and Their Consequences
Topic overviewFieldsNewton's lawGravitational field strengthGravitational potentialOrbits of planets and satellitesCoulomb's lawElectric field strengthElectric potentialCapacitanceParallel plate capacitorEnergy stored by a capacitorCapacitor charge and dischargeMagnetic flux densityMoving charges in a magnetic fieldMagnetic flux and flux linkageElectromagnetic inductionAlternating currentsTransformers
Nuclear Physics
AstrophysicsOptional topic
Topic overviewAstronomical telescope consisting of two converging lensesReflecting telescopesSingle dish radio telescopes, I-R, U-V and X-ray telescopesAdvantages of large diameter telescopesClassification by luminosityAbsolute magnitude, MClassification by temperature, black-body radiationPrinciples of the use of stellar spectral classesThe Hertzsprung-Russell (HR) diagramSupernovae, neutron stars and black holesDoppler effectHubble's lawQuasarsDetection of exoplanets
Medical PhysicsOptional topic
Topic overviewPhysics of visionDefects of vision and their correction using lensesEar as a sound detection systemSensitivity and frequency responseDefects of hearingSimple ECG machines and the normal ECG waveformUltrasound imagingFibre optics and endoscopyMagnetic resonance (MR) scannerThe physics of diagnostic X-raysImage detection and enhancementAbsorption of X-raysCT scannerImaging techniquesHalf-lifeGamma cameraUse of high-energy X-raysUse of radioactive implantsImaging comparisons
Engineering PhysicsOptional topic
Turning Points in PhysicsOptional topic
Topic overviewCathode raysThermionic emission of electronsSpecific charge of the electronPrinciple of Millikan's determination of the electronic charge, eNewton's corpuscular theory of lightSignificance of Young's double slits experimentElectromagnetic wavesThe discovery of photoelectricityWave–particle dualityElectron microscopesThe Michelson-Morley experimentEinstein's theory of special relativityTime dilationLength contractionRelativistic mass and energy
ElectronicsOptional topic
Topic overviewMOSFET (metal-oxide semiconducting field-effect transistor)Zener diodePhotodiodeHall effect sensorDifference between analogue and digital signalsLC resonance filtersThe ideal operational amplifierInverting amplifier configurationNon-inverting amplifier configurationSumming amplifier configurationReal operational amplifiersCombinational logicSequential logicAstablesPrinciples of communication systemsTransmission mediaTime-division multiplexingAmplitude (AM) and frequency modulation (FM) techniques
Turning Points in Physics
- 15 subtopics
- 47 things to know
- Paper 3, section B
- Paper 3 Section B, one optional topic of five
What Turning Points in Physics covers
Turning points in physics is one of the five optional topics, sat on Paper 3. It follows three arguments that changed the subject: the discovery of the electron, the long dispute over whether light is a wave or a particle, and the experiment that led to special relativity.
Where it is assessed
Paper 3, section B
One optional topic, chosen from five.
Check the AQA specification ↗The 15 subtopics
Each one has its own page.
- Cathode raysDischarge tubes, why low pressure is needed, and how electrons are accelerated.Open →
- Thermionic emission of electronsReleasing electrons from a heated metal, and the work done accelerating them through a potential difference.Open →
- Specific charge of the electronThomson's experiment, balancing the electric and magnetic fields, and what the result implied.Open →
- Principle of Millikan's determination of the electronic charge, eThe oil drop experiment, Stokes' law, terminal speed, and the quantisation of charge.Open →
- Newton's corpuscular theory of lightHow the corpuscular theory explained reflection and refraction, and where it conflicted with wave theory.Open →
- Significance of Young's double slits experimentWhy interference could not be explained by particles, and when wave theory was accepted.Open →
- Electromagnetic wavesMaxwell's prediction of the speed of light, and Hertz's and Fizeau's confirmations.Open →
- The discovery of photoelectricityThe ultraviolet catastrophe and black-body radiation, Planck's quantum, why classical wave theory failed to explain photoelectric emission, and Einstein's photon explanation and photoelectric equation.Open →
- Wave–particle dualityDe Broglie's hypothesis that matter has wave properties, the equations λ = h/p and λ = h/√(2meV), and how low-energy electron diffraction confirmed it, including how electron speed changes the rings.Open →
- Electron microscopesThe de Broglie wavelength of an accelerated electron, and the transmission and scanning tunnelling microscopes.Open →
- The Michelson-Morley experimentThe apparatus, what an ether would have produced, and what the null result meant.Open →
- Einstein's theory of special relativityInertial frames, the two postulates, and the consequences of a constant speed of light.Open →
- Time dilationThe Lorentz factor, proper time, and the muon evidence.Open →
- Length contractionProper length, contraction along the direction of motion, and when the effect becomes significant.Open →
- Relativistic mass and energyThe relativistic equations for total energy, rest energy and mass, how mass and kinetic energy vary with speed, why a particle with mass never reaches the speed of light, and Bertozzi's direct test of kinetic energy against speed.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Why must the pressure be low, and what gives the electrons kinetic energy?
Key term
What are cathode rays now known to consist of?
Numbers
What happens to electrons when a metal is heated, and how is work on an electron calculated?
Numbers
How is v = √(2eV/m) derived, and what must an electron overcome to escape?
Key term
Which electrons in a heated metal are able to escape during thermionic emission?
Numbers
How was Thomson's magnetic field oriented, how did balancing the fields give the electron velocity, and what is v for E = 33500 V m⁻¹ and B = 0.0053 T?
Numbers
How is specific charge found from a circular path, and what does r represent?
Numbers
What did Thomson conclude about atomic structure, and why does high specific charge mean small mass?
Numbers
State the approximate value of the specific charge of the hydrogen ion
Numbers
What holds at terminal speed for a falling droplet, and how is Stokes' law then used?
Numbers
How is the mass of a droplet found, and what pattern did Millikan see in the charges?
Process
What happens when a field is applied to a falling droplet, and how does drag change with speed?
Key term
What does quantisation of electric charge mean?
Numbers
How did each theory explain light travelling in straight lines and reflecting?
Key term
What opposing predictions did the two theories make about the speed of light in a dense medium?
Numbers
What non-scientific factor contributed significantly to the preference for Newton's corpuscular theory over Huygens' wave theory?
Process
What happens when waves from two slits arrive in phase and out of phase?
Process
What property did Young's experiment demonstrate, and when was wave theory accepted?
Numbers
What is Maxwell's formula for the speed of light, and which constants appear in it?
Numbers
How did Hertz generate and detect radio waves, and how did he measure their wavelength?
Numbers
How did Fizeau's measurement support Maxwell, and why did it matter?
Process
Explain what occurred at the critical rotation speed in Fizeau's toothed wheel experiment
Numbers
What was the ultraviolet catastrophe, how did Planck resolve it, and how does the energy of each packet depend on frequency?
Numbers
What is the work function, and how does a photon interact with an electron?
Numbers
What was de Broglie's hypothesis, and what did Einstein show about light?
Numbers
When is λ = h/√(2meV) used, how does electron diffraction show wave behaviour, and what happens to the rings as voltage rises?
Process
In electron diffraction experiments, what happens to the de Broglie wavelength when the speed of the electrons is decreased?
Numbers
What do the symbols in λ = h/p mean, and what happens to an accelerated electron?
Numbers
How is p = √(2mₑeV) derived for an accelerated electron?
Numbers
How is de Broglie wavelength expressed using accelerating voltage, and what voltage is needed?
Numbers
State the typical maximum thickness for a TEM specimen
Key term
In constant-current mode STM, how is surface topography mapped?
Process
Where do the two beams travel after the beam splitter, and what happens at each mirror?
Key term
Where do the returning beams meet again, where do they then travel, and what do they produce?
Numbers
What was expected when the apparatus was rotated, what was actually observed, and what did the null result show?
Process
What did the null result of the Michelson-Morley experiment imply about absolute motion?
Numbers
What is an inertial frame, and how can Newton's first law test for one?
Key term
What is Einstein's first postulate, and is a train at constant velocity an inertial frame?
Numbers
What is the Lorentz factor, and how does it relate proper time to dilated time?
Numbers
Why does γ grow as v approaches c, what happens to time dilation then, and why is it negligible at everyday speeds?
Numbers
What is the proper lifetime of a muon?
Numbers
What do l₀ and c represent in the length contraction formula?
Numbers
How does contracted length relate to proper length, and when does the effect matter?
Process
Calculate the total energy and kinetic energy of an electron moving at 0.80c (rest energy of electron = 0.511 MeV).
Process
State the equation for the rest energy of a particle.
Process
State the equation for the relativistic mass of a particle moving at speed v.
Take Turning Points in Physics further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Inertial frame vs Non-inertial frame
Inertial frame: reference frame with no acceleration. Non-inertial frame: accelerating reference frame requiring apparent forces.
Photoelectric effect vs Compton effect
Photoelectric effect: electron emission caused by incident photons. Compton effect: photon wavelength increase after electron scattering.
Matter wave vs Electromagnetic wave
Matter wave: wave associated with a moving particle. Electromagnetic wave: oscillating electric and magnetic fields.
Questions from this topic
Each one with the model answer underneath.
- 1
In a discharge tube, what must be applied across the two electrodes to produce cathode rays?
Model answer
A high voltage must be applied across the electrodes.
- 2
Describe the physical construction of a discharge tube in terms of its electrodes.
Model answer
The electrodes are sealed inside a glass tube.
- 3
What condition regarding the gas inside a discharge tube is required for cathode ray production?
Model answer
The gas must be at low pressure.
- 4
What is the cathode in a discharge tube?
Model answer
The cathode is the negative electrode from which cathode rays originate.
- 5
Where do the electrons in a discharge tube originate from?
Model answer
Electrons are emitted from the cathode.
- 6
What is the anode in a discharge tube?
Model answer
The anode is the positive electrode towards which cathode rays travel.
What is inside Levo
Six ways to work the same material.
Turning Points in Physics revision questions
- What does Turning Points in Physics cover in AQA A-Level Physics?
- 15 subtopics: cathode rays, thermionic emission of electrons, specific charge of the electron, principle of millikan's determination of the electronic charge, e, newton's corpuscular theory of light, significance of young's double slits experiment, electromagnetic waves, the discovery of photoelectricity, wave–particle duality, electron microscopes, the michelson-morley experiment, einstein's theory of special relativity, time dilation, length contraction and relativistic mass and energy. Each one has its own page with questions and model answers.
- How is Turning Points in Physics organised?
- By the AQA 7408 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Turning Points in Physics, on a schedule.
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