Key term
Eduqas A-Level Physics A420QS
Basic Physics
Kinematics
Dynamics
Energy Concepts
Circular Motion
Vibrations
Topic overviewDefining simple harmonic motionFrequency, period, amplitude and phaseThe displacement equation for simple harmonic motionVelocity in simple harmonic motionDisplacement and velocity graphsThe mass-spring oscillatorThe simple pendulumEnergy in simple harmonic motionFree oscillation and dampingForced oscillation and resonance
Kinetic Theory
Thermal Physics
Conduction of Electricity
Resistance
Topic overviewPotential difference and the voltResistance, Ohm's law and the ohmI–V characteristics of a metal wire and a filament lampElectrical power and energy transferThe microscopic origin of resistanceResistivity and the equation R = ρl/AResistance and temperatureSuperconductivity and the transition temperatureHigh temperature superconductors and their uses
D.C. Circuits
Capacitance
Solids Under Stress
Electrostatic and Gravitational Fields of Force
Topic overviewElectric field strength and Coulomb's lawGravitational field strength and Newton's law of gravitationField lines and equipotential surfacesElectric potential and potential energyGravitational potential and potential energyResultant fields and potentials from several sourcesComparing electric and gravitational fields
Using Radiation to Investigate Stars
Orbits and the Wider Universe
Topic overviewKepler's laws of planetary motionNewton's law of gravitation applied to planets and satellitesDeriving Kepler's third law for a circular orbitUsing orbital data to find the mass of the central objectGalactic rotation curves and dark matterThe centre of mass of a two-body systemThe Doppler shift of spectral lines and radial velocityMasses in a double system from radial velocity dataHubble's law, the age of the universe and its fate
The Nature of Waves
Wave Properties
Topic overviewDiffraction at slits and obstaclesWavelength, slit width and the spread of the beamThe principle of superpositionCoherence and the conditions for interferencePath difference and the interference conditionsYoung's double slit experimentThe historical importance of Young's experimentThe diffraction gratingComparing the grating with the double slitStationary waves
Refraction of Light
Photons
Topic overviewPhotons and the quantum of lightDemonstrating the photoelectric effectThe vacuum photocell and stopping potentialEinstein's equation and the energy graphThe electromagnetic spectrum and photon energiesLine emission and line absorption spectraAtomic energy levelsIonisation energy from an energy level diagramElectron diffraction and the de Broglie relationship
Lasers
Nuclear Decay
Topic overviewSpontaneous decay and the nature of α, β and γ radiationNuclear transformation equations and nuclide notationDistinguishing α, β and γ by ionisation, penetration and rangeBackground radiation and gamma intensity with distanceActivity, the becquerel and the decay constantThe exponential decay law and half-life
Particles and Nuclear Structure
Topic overviewThe Rutherford alpha particle scattering experimentCoulomb repulsion in the plum pudding and Rutherford modelsQuarks and leptons: the first generationAntiparticles, annihilation and their symbolsHadrons: baryons, antibaryons and mesonsQuark composition of the proton, neutron and pionsThe four fundamental interactionsConservation laws in particle reactions
Nuclear Energy
Magnetic Fields
Topic overviewThe motor effect and Fleming's left-hand ruleF = BIl sinθ and measuring magnetic flux densityThe force on a moving charge, F = Bqv sinθThe Hall effect and the Hall probeMagnetic fields due to a straight wire and a solenoidForces between current-carrying conductorsCharged particle beams and accelerators
Electromagnetic Induction
Option A: Alternating CurrentsOption A
Topic overviewElectromagnetic induction in a rotating coilFrequency, period, peak and rms valuesMean power dissipated in a resistorUsing an oscilloscope to measure voltage and frequencyInductors in a.c. circuits and inductive reactanceCapacitors in a.c. circuits and capacitive reactancePhasors, phase angle and impedanceResonance in the series RCL circuit and the Q factor
Option B: Medical PhysicsOption B
Topic overviewThe nature and properties of X-raysX-ray production and controlling the beamAttenuation of X-rays and half-value thicknessX-ray imaging, fluoroscopy and radiographyComputed tomography scanningUltrasound generation and acoustic impedanceUltrasound scanning and the Doppler techniqueMagnetic resonance and MRIRadiation effects on living matter and dosimetryRadionuclide tracers, the gamma camera and PET
Option C: The Physics of SportsOption C
Topic overviewCentre of gravity, stability and topplingMoments in muscle systems and other sporting contextsImpulse and Newton's second law in sportThe coefficient of restitutionMoment of inertiaAngular acceleration, torque and angular momentumConservation of angular momentum and rotational energyProjectiles, Bernoulli's equation and drag
Option D: Energy and the EnvironmentOption D
Mathematical Requirements (Appendix C)
Topic overviewUnits, prefixes and standard formSignificant figures and arithmetic meansUncertainty and how uncertainties combineRatios, proportionality and order of magnitude estimatesRearranging and solving physics equationsLogarithms, exponentials and decayResolving vectors, Pythagoras and trigonometryRadians, small angles, areas and volumesStraight-line graphs, gradients and interceptsTangents, areas under curves and logarithmic plots
Using Radiation to Investigate Stars
The inverse square law, stellar distance and multiwavelength astronomy
- 3 things to know
- Component 2
Overview
Recall questions on how intensity falls with distance, using the luminosity and the measured intensity to find a distance, worked calculations, and why observations in more than one region of the electromagnetic spectrum reveal what visible light alone cannot.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Why does the radiation received from a star obey an inverse square law?
Key term
By what factor does the intensity received fall if the distance to a star is trebled?
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the inverse square law for the intensity of radiation received from a star, defining every symbol and its unit.
Model answer
The intensity is I = L/(4πd²), where I is the intensity in W m⁻², L is the star's luminosity in watts and d is its distance from the observer in metres.
- 2
Why does the radiation received from a star obey an inverse square law?
Model answer
The star radiates its power equally in all directions, so at a distance d that power is spread over the surface of a sphere of area 4πd², and the power per square metre falls as the inverse square of the distance.
- 3
What assumption about the space between a star and the observer does the inverse square law make?
Model answer
It assumes the intervening space is empty, so none of the radiation is absorbed or scattered before it arrives.
- 4
By what factor does the intensity received fall if the distance to a star is trebled?
Model answer
The intensity falls to one ninth of its value, because it is inversely proportional to the square of the distance.
- 5
Calculate the intensity of solar radiation at the Earth, taking the Sun's luminosity as 3.9 × 10²⁶ W and the Earth's distance as 1.50 × 10¹¹ m.
Model answer
The intensity is I = 3.9 × 10²⁶ ÷ (4π × (1.50 × 10¹¹)²) = 1.4 × 10³ W m⁻². Multiplying 1380 W m⁻² by 4π × 2.25 × 10²² m² returns 3.9 × 10²⁶ W.
- 6
A star of luminosity 4.0 × 10²⁸ W lies 3.0 × 10¹⁸ m away. Calculate the intensity of its radiation at the Earth.
Model answer
The intensity is I = 4.0 × 10²⁸ ÷ (4π × (3.0 × 10¹⁸)²) = 3.5 × 10⁻¹⁰ W m⁻². Multiplying 3.54 × 10⁻¹⁰ W m⁻² by 1.131 × 10³⁸ m² returns 4.0 × 10²⁸ W.
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