Key term
CCEA A-Level Physics 1210
Physical Quantities, Scalars and Vectors
Moments and Equilibrium
Linear Motion and Dynamics
Newton's Laws of Motion
Linear Momentum and Impulse
Work, Energy and Power
Current, Charge and Potential Difference
Resistance and Resistivity
Topic overviewResistance and Ohm's lawOhmic and non-ohmic behaviourResistors in series and in parallelInvestigating current, voltage and resistance in series and parallel circuitsElectrical power and energy in resistive circuitsResistivity and the equation R = ρl/AMeasuring the resistivity of a metalCurrent–voltage characteristics of a conductor, a lamp and a diodeResistance, temperature and superconductivity
Internal Resistance and Potential Dividers
Topic overviewInternal resistance and terminal potential differenceConsequences of internal resistance for external circuitsMeasuring electromotive force and internal resistanceThe potential divider and variable outputPotential dividers in lighting and heating control circuitsLoaded potential dividers and output voltage calculations
Waves
Refraction
Lenses
Superposition, Interference and Diffraction
Topic overviewSuperposition of wavesStanding waves, nodes and antinodesStanding waves on stretched stringsStanding waves in a pipe closed at one endMeasuring the speed of sound with a resonance tubeConditions for observable interferencePath difference and phase differenceYoung's double slitDiffraction at a single slitThe diffraction grating
Quantum Physics
Wave-Particle Duality
Astronomy
Practical Skills and Data Analysis
Topic overviewChoosing and using measuring instrumentsPrecision, accuracy and recording measurementsUsing the cathode ray oscilloscope to measure voltage and frequencyTables, graphs and presenting resultsLinearising a relationship and using the gradientAbsolute and percentage uncertaintyCombining uncertainties and uncertainty on a graphRandom and systematic error, reliability and refining an experiment
Deformation of Solids
Thermal Physics
Topic overviewBoyle's law, Charles's law and the pressure lawThe ideal gas equation pV = nRTThe Avogadro constant, the mole and pV = NkTInternal energy and the distribution of molecular energyThe kinetic theory equation pV = ⅓Nm⟨c²⟩Average molecular kinetic energy and temperatureAbsolute zero and the kelvin scaleSpecific heat capacity and the electrical method
Uniform Circular Motion
Simple Harmonic Motion
Topic overviewDefining simple harmonic motion and a = −ω²xDisplacement, velocity and acceleration: x = A cos ωtThe simple pendulum and T = 2π√(l/g)The loaded spiral spring and T = 2π√(m/k)SHM graphs and finding velocity from a gradientFree vibrations, forced vibrations and resonanceDamping: light, critical and over-damping
The Nucleus and Radioactive Decay
Topic overviewAlpha-particle scattering and the nuclear atomNuclear radius and nucleon numberThe density of nuclear matterAlpha, beta and gamma radiation: nature, penetration and rangeNuclear equations and changes in nucleon and proton numberThe random and exponential nature of radioactive decayActivity, the decay constant and A = −λNExponential decay calculations with A = A₀e^(−λt)Half-life and measuring it
Nuclear Energy, Fission and Fusion
Gravitational Fields
Electric Fields
Capacitors
Magnetic Fields
Charged Particles and Accelerators
Astronomy
The classical Doppler effect
- 3 things to know
- Unit AS 2
Overview
Recall questions on what the Doppler effect is and the ambulance siren as the everyday case, the wavefront explanation for an approaching and a receding source, the wavelength and frequency equations, worked calculations both ways, whether the emitted frequency itself changes, the null result for transverse motion, and the derivation of Δλ/λ = v/c.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State the classical Doppler equation in terms of frequency for a moving source and a stationary observer.
Key term
Explain in terms of wavefronts why an approaching source produces a shorter wavelength.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the Doppler effect?
Model answer
The Doppler effect is the change in the observed frequency and wavelength of a wave that occurs when the source and the observer are moving relative to one another.
- 2
Describe what is heard as an ambulance siren approaches, passes and drives away.
Model answer
The note is heard at a higher pitch than normal while the ambulance approaches, drops suddenly as it passes, and is heard at a lower pitch than normal as it recedes.
- 3
Explain in terms of wavefronts why an approaching source produces a shorter wavelength.
Model answer
The source moves forward between emitting one wavefront and the next, so each new wavefront starts from a point closer to the observer and the wavefronts ahead of the source are bunched together.
- 4
Explain in terms of wavefronts why a receding source produces a longer wavelength.
Model answer
The source moves away between emitting successive wavefronts, so each new wavefront starts further from the observer and the wavefronts behind the source are stretched apart.
- 5
State the classical equation for the wavelength received by a stationary observer from a receding source, defining each symbol.
Model answer
λ' = λ(c + v)/c, where λ' is the received wavelength in metres, λ is the wavelength emitted by the source at rest in metres, v is the speed of the source in m s⁻¹ and c is the speed of the wave in the medium in m s⁻¹.
- 6
State the classical equation for the wavelength received by a stationary observer from an approaching source.
Model answer
λ' = λ(c − v)/c, where λ' is the received wavelength, λ is the wavelength emitted by the source at rest, v is the speed of the approaching source and c is the wave speed, all in SI units.
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