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
Superposition, Interference and Diffraction
Path difference and phase difference
- 3 things to know
- Unit AS 2
Overview
Recall questions on the definition of path difference, the whole-wavelength and half-odd-wavelength conditions for constructive and destructive interference, the same conditions in terms of phase, why the central fringe is always bright, worked examples with given path differences, and two loudspeakers wired out of phase.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State the condition on path difference for destructive interference.
Key term
State the conditions for constructive and destructive interference in terms of phase difference.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Define path difference.
Model answer
The path difference at a point is the difference between the distances travelled from each of the two sources to that point, measured in metres.
- 2
State the condition on path difference for constructive interference.
Model answer
Constructive interference occurs where the path difference is a whole number of wavelengths, that is nλ where n is 0, 1, 2, and so on.
- 3
State the condition on path difference for destructive interference.
Model answer
Destructive interference occurs where the path difference is an odd number of half wavelengths, that is (n + ½)λ.
- 4
State the conditions for constructive and destructive interference in terms of phase difference.
Model answer
Constructive interference occurs when the phase difference is a whole number of full cycles, that is 2πn radians, and destructive interference when it is an odd multiple of π radians.
- 5
Waves from two coherent sources arrive at a point with a path difference of 1.5 wavelengths. What is observed there?
Model answer
The point is dark or quiet, because an odd number of half wavelengths means the waves arrive in antiphase and cancel.
- 6
Waves from two coherent sources arrive at a point with a path difference of exactly two wavelengths. What is observed there?
Model answer
The point is bright or loud, because a whole number of wavelengths means the waves arrive in phase and reinforce.
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