Key term
WJEC AS-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
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
Refraction of Light
- 6 subtopics
- 18 things to know
- AS Unit 2
What Refraction of Light covers
Refraction of Light is examined on AS Unit 2 of WJEC Physics, Electricity and Light. 79 recall questions across 6 subtopics.
The 6 subtopics
Each one has its own page. WJEC AS Physics students sit this topic in the first year.
- What refraction is and why it happensRecall questions on What refraction is and why it happens.Open →
- Refractive index and Snell's lawRecall questions on Refractive index and Snell's law.Open →
- Total internal reflection and optical fibresRecall questions on Total internal reflection and optical fibres.Open →
- The wave model of refraction and n₁v₁ = n₂v₂Recall questions on The wave model of refraction and n₁v₁ = n₂v₂.Open →
- Snell's law at a boundary between two mediaRecall questions on Snell's law at a boundary between two media.Open →
- Optical fibres: core, cladding and pulse broadeningRecall questions on core, cladding broadening and pulse broadening.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Process
Why does a light ray change direction at a boundary?
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When using Snell's law to calculate the angle of refraction, what information must be known?
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Explain in terms of wavefronts why a beam changes direction when it meets a boundary obliquely and slows down.
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Explain why light travelling along the normal enters a new medium without changing direction.
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Why is the refractive index of a vacuum exactly 1?
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Explain why the ray emerging from a parallel-sided block is parallel to the incident ray.
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What does the refractive index of a material indicate?
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State the two conditions for total internal reflection to occur.
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Define the critical angle.
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Why does a triangular prism deviate a ray of light instead of returning it parallel to its original direction?
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What is meant by crossover in a bundle of optical fibres?
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What is material dispersion in an optical fibre?
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Why does refraction occur when light passes between two different media?
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What does Snell's law describe?
Numbers
Calculate the critical angle for a glass–air boundary where the glass has refractive index 1.50.
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Why does a glass prism spread white light into a spectrum?
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Why is a very nearly monochromatic source used to send signals along a long optical fibre?
Take Refraction of Light further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Refraction vs Total internal reflection
Refraction: the change of direction of a wave as its speed changes at a boundary. Total internal reflection: the complete reflection back into the denser medium beyond the critical angle.
The angle of incidence vs The critical angle
The angle of incidence: the angle between the incoming ray and the normal. The critical angle: the angle in the denser medium at which the refracted ray runs along the boundary.
Questions from this topic
Each one with the model answer underneath.
- 1
What is refraction?
Model answer
Refraction is the change in direction of a wave when it passes from one medium to another due to a change in speed.
- 2
Why does refraction occur when light passes between two different media?
Model answer
Refraction occurs because the speed of light changes when it enters a different medium, causing the wave to change direction.
- 3
In which direction does light bend when it travels from a less optically dense medium into a more optically dense medium?
Model answer
Light bends towards the normal.
- 4
A light ray passes from air into glass. How does its direction change relative to the normal?
Model answer
The light ray bends towards the normal because it is entering a more optically dense medium.
- 5
What happens to the direction of a light ray as it exits from water into air?
Model answer
The light ray bends away from the normal because it is entering a less optically dense medium.
- 6
What is the normal in the context of refraction?
Model answer
The normal is an imaginary line perpendicular to the boundary between two media at the point of incidence.
What is inside Levo
Six ways to work the same material.
Refraction of Light revision questions
- Is Refraction of Light examined at AS in WJEC Physics?
- Yes. It sits in AS Unit 2, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
- What does Refraction of Light cover in WJEC AS-Level Physics?
- 6 subtopics: what refraction is and why it happens, refractive index and snell's law, total internal reflection and optical fibres, the wave model of refraction and n₁v₁ = n₂v₂, snell's law at a boundary between two media and optical fibres: core, cladding and pulse broadening. Each one has its own page with questions and model answers.
- How is Refraction of Light organised?
- By the WJEC 1420QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Refraction of Light, 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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