Key term
OCR A-Level Physics B H557
Planning
Implementing
Analysis
Evaluation
Practical Skills
Use of Apparatus and Techniques
Fundamental Data Analysis
Imaging and Signalling
Topic overviewReal images and the curvature of wave-frontsLens power and focal lengthThe thin lens equation and the Cartesian conventionLinear magnificationMeasuring the power and focal length of a converging lensImages as arrays of numbersBits, bytes and the information in an imageEnhancing a digital imageWave-forms, frequency and wave speedSampling and digitising an analogue signalNoise, resolution and digital transmissionPolarisation of electromagnetic waves
Sensing
Topic overviewCurrent and the flow of chargePotential difference, e.m.f. and energy transferResistance, conductance and Ohm's lawSeries and parallel combinationsPower and energy in electric circuitsInternal resistance and e.m.f.Kirchhoff's laws and conservation in circuitsResistivity and conductivityCharge carrier number density in metals, semiconductors and insulatorsCurrent-potential difference characteristics and circuit componentsThe potential dividerSensing circuits and calibration
Mechanical Properties of Materials
Topic overviewElastic and plastic deformation and fractureHooke's law and force-extension graphsElastic strain energyStress, strain and the Young modulusMeasuring the Young modulus and fracture stress of a metalDescribing and comparing materialsMetals, ceramics and polymersDirect evidence for the size and spacing of particles
Waves and Quantum Behaviour
Topic overviewWaves, phase and superpositionStanding waves on stringsStanding waves in air columns and the speed of soundRefraction, refractive index and Snell's lawTwo-slit interferenceDiffraction at a narrow apertureThe diffraction gratingMeasuring the wavelength of lightPhotons and the quantum E = hfEvidence that photons exchange energy in quantaQuantum behaviour: phasors and probability of arrivalElectron diffraction and the de Broglie wavelength
Space, Time and Motion
Topic overviewScalars, vectors and their representationResolving and adding vectorsDescribing motion: displacement, velocity and accelerationMotion graphsThe kinematic equations for constant accelerationProjectiles and motion in two dimensionsMeasuring motion in the laboratoryDetermining the acceleration of free fallNewton's laws of motionTerminal velocity and resistive forcesMomentum and impulseConservation of momentum and collisionsWork, energy and its conservationPower and modelling motion in small time steps
Creating Models
Topic overviewCapacitance and charge storageEnergy stored on a capacitorCapacitor discharge and the exponential modelThe time constant of an RC circuitCharging a capacitorInvestigating capacitor charge and dischargeRadioactive decay as a random processActivity, decay constant and half-lifeDetermining the half-life of an isotopeIterative numerical models of exponential changeExponential curves on linear and logarithmic scalesSimple harmonic motion: the defining relationshipSolutions and graphs of simple harmonic motionModelling oscillations step by stepEnergy in simple harmonic motionPeriod of a mass–spring system and a simple pendulumFree and forced vibrations, damping and resonance
Out Into Space
Topic overviewGravitational and kinetic energy changesMotion in a uniform gravitational fieldGravitational force and the radial fieldGravitational field strengthGravitational potential energy in a radial fieldGravitational potential and equipotentialsGraphs and diagrams of gravitational fieldsAngular velocity and motion in a horizontal circleCircular gravitational orbits
Our Place in the Universe
Matter: Very Simple
Topic overviewEnergy transfer and specific thermal capacityFinding specific thermal capacity by an electrical methodIdeal gases and the gas lawsInvestigating the gas laws and absolute zeroMoles, the Avogadro constant and the Boltzmann constantThe equation of state for an ideal gasImpulse and force–time graphsThe kinetic theory of ideal gasesTemperature, average energy per particle and internal energyRandom walk of molecules in a gas
Matter: Hot or Cold
Electromagnetism
Topic overviewMagnetic flux, B-fields and flux linkageElectromagnetic induction: Faraday's and Lenz's lawsGraphs of current, flux and induced e.m.f.The dynamoThe transformerEddy currents and real transformersForces on current-carrying conductorsMagnetic circuits, permeance and machine designInvestigating induction, flux density and transformers
Charge and Field
Topic overviewThe uniform electric fieldRadial fields and the inverse square lawElectric potential and potential energyField and potential graphsField lines and equipotential surfacesThe electronvolt and accelerating chargesMillikan's experiment and the discreteness of chargeMoving charges in magnetic fieldsComparing electric and gravitational fields
Probing Deep Into Matter
Topic overviewParticle accelerators and high-energy beamsScattering and the nuclear atomPaths of scattered particles and closest approachDiscrete energy levels in atomsElectron standing waves and the confined electronQuarks, hadrons and leptonsConservation laws and nuclear equationsCharged particles in detectors and magnetic fieldsRelativistic energy and the relativistic factor
Ionising Radiation and Risk
Topic overviewThe nature of ionising radiationsEffects on living tissue and radiation safetyAbsorbed dose, effective dose and riskBinding energy and nuclear stabilityThe Nuclear Valley and modes of decayFission, fusion and nuclear powerActivity, half-life and the decay constantInvestigating absorption and half-life
Imaging and Signalling
- 12 subtopics
- 36 things to know
- Components 01, 02 and 03
What Imaging and Signalling covers
Imaging and Signalling is examined in all three written papers — the specification states that Components 01, 02 and 03 each assess content from across all the teaching modules, so nothing is confined to one paper. It covers real images and the curvature of wave-fronts, lens power and focal length, the thin lens equation and the Cartesian convention, linear magnification, measuring the power and focal length of a converging lens, images as arrays of numbers, bits, bytes and the information in an image, Enhancing a digital image, wave-forms, frequency and wave speed, sampling and digitising an analogue signal, noise, resolution and digital transmission and polarisation of electromagnetic waves.
Where it is assessed
Components 01, 02 and 03
Every module can be assessed on any of the three papers.
Check the OCR specification ↗The 12 subtopics
Each one has its own page.
- Real images and the curvature of wave-frontsRecall questions on defining wave-front curvature, the fixed amount a thin lens adds, wave-fronts from a distant object, the standard ray constructions, and why the image is inverted.Open →
- Lens power and focal lengthRecall questions on lens power P = 1/f and the dioptre, converting between power and focal length, the positive power of a converging lens, the thin lens relationship in curvature form, adding the powers of lenses in contact, why opticians use dioptres, the curvature a lens adds to a wave-front, and how refractive index and surrounding water change power.Open →
- The thin lens equation and the Cartesian conventionRecall questions on the sign convention for object and image distances, calculating image position, focal length and power, the least possible object–image separation, and covering half a lens.Open →
- Linear magnificationRecall questions on relating magnification to object and image distances, why it has no unit, what a negative value means, image heights in cameras and projectors, and distant objects.Open →
- Measuring the power and focal length of a converging lensRecall questions on the distant-object estimate, the illuminated-object and screen method, plotting reciprocal distances, locating the sharpest image, systematic error in the distances, and testing a very weak lens.Open →
- Images as arrays of numbersRecall questions on pixels, bits and bytes, greyscale images as arrays of numbers, grey levels and bits per pixel, image resolution and pixel size, why stored numbers allow processing, false colour and thermal images, noise, and the bits needed for colour and 24-bit images.Open →
- Bits, bytes and the information in an imageRecall questions on image information from pixels and bits per pixel, converting to bytes, the alternatives and grey levels a number of bits gives, logarithms to base two, and coarse quantisation.Open →
- Enhancing a digital imageRecall questions on changing brightness and contrast by adding to and multiplying pixel values, saturation, smoothing to reduce noise and its cost, median filters, edge detection, why processing cannot add information, false colour and raised contrast in medical images, and repeated smoothing.Open →
- Wave-forms, frequency and wave speedRecall questions on reading the period and amplitude from a wave-form, f = 1/T, v = fλ for radio waves and ultrasound, how wavelength limits the detail of an ultrasound scan, peak-to-peak voltage, and the wave-forms of pure and noisy signals.Open →
- Sampling and digitising an analogue signalRecall questions on analogue and digital signals, sampling and turning samples into binary numbers, the resolution of a digitisation, the minimum sampling rate and what goes wrong below it, filtering before digitising, the staircase shape and how bits and sampling rate change it, sampling music 44 100 times per second, and quantisation error.Open →
- Noise, resolution and digital transmissionRecall questions on noise and the limit it sets on useful bits, b = log₂(Vₜₒₜₐₗ/Vₙₒᵢₛₑ) and why it is rounded down, rate of transmission as samples per second × bits per sample, the highest frequency a sampling rate can record, the advantages and disadvantages of digital transmission, and regenerating pulses before noise grows too large.Open →
- Polarisation of electromagnetic wavesRecall questions on plane polarisation and why only transverse waves show it, polarising filters, rotating one of two filters and crossed polarisers, demonstrating polarisation with microwaves and a metal grille, unpolarised lamp light, polarising sunglasses, stressed plastic between crossed polarisers, and liquid crystal displays.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Explain why the magnification of a distant object is always very small.
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Describe how to determine the power of a converging lens using an illuminated object, a screen and the lens equation.
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Explain how polarising sunglasses reduce glare from a wet road.
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State the unit of lens power and its SI equivalent.
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State the thin lens equation as used in the Cartesian convention.
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What is a pixel?
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State how the amount of information in an image is calculated.
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How is the brightness of a stored image increased?
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State the relationship between frequency and period.
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What is an analogue signal?
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What is noise on a signal?
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What is a real image?
Numbers
Calculate the power of a converging lens of focal length 25 cm.
Key term
In the Cartesian convention, which direction along the axis is taken as positive?
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Define linear magnification.
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Explain why the distant-object method gives the focal length directly.
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Define a bit.
Numbers
An image is 200 pixels by 300 pixels with 4 bits per pixel. Calculate the amount of information it holds.
Key term
How is the contrast of a stored image increased?
Numbers
A wave-form repeats every 20 μs. Calculate its frequency.
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What is a digital signal?
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Explain why noise sets a limit on the useful number of bits per sample.
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Explain why only transverse waves can be polarised.
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How is the curvature of a spherical wave-front defined?
Numbers
A lens has a power of +8.0 D. Calculate its focal length.
Numbers
An object is 0.30 m in front of a converging lens of focal length 0.20 m. Calculate the image distance.
Key term
State the relationship between linear magnification and the object and image distances.
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State the gradient expected from a graph of 1/v against 1/u, and what it checks.
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Define a byte.
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An image holds 240 000 bits of information. Express this in bytes.
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Explain why adding a constant to every pixel does not change the contrast.
Numbers
A wave-form shows 4 complete cycles in 10 ms. Calculate the frequency.
Key term
State the minimum rate at which a signal must be sampled.
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State the relationship giving the maximum useful number of bits for a noisy signal.
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Describe what is observed when unpolarised light passes through two polarising filters and one is slowly rotated.
Take Imaging and Signalling further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Resolution vs Number of grey levels
Resolution: the size that the smallest distinguishable detail has in a stored image, set by the area each pixel covers on the object. Number of grey levels: How many separate brightness steps a stored image can hold, fixed by the binary digits kept for each pixel.
Bit vs Byte
Bit: a binary digit, the smallest unit of information, able to hold one of two alternatives. Byte: A group of eight binary digits, and the unit file sizes are normally quoted in.
Sampling rate vs Bits per sample
Sampling rate: how many measurements of a signal are taken each second, which must exceed twice the highest frequency present if that frequency is to be captured. Bits per sample: How many binary digits record each measured value, which fixes how finely that value can be recorded and how many steps it can take.
Questions from this topic
Each one with the model answer underneath.
- 1
What is a real image?
Model answer
A real image is formed where light rays actually converge, so it can be caught on a screen placed at that position.
- 2
Explain what a thin converging lens does to a wave-front passing through it.
Model answer
It adds a fixed amount of curvature to every wave-front, making a diverging wave-front less divergent or turning it into a converging one.
- 3
How is the curvature of a spherical wave-front defined?
Model answer
Curvature is 1/r, where r is the radius of curvature of the wave-front, so it is measured in m⁻¹.
- 4
Why does a wave-front become less curved the further it travels from a point source?
Model answer
Its radius of curvature grows with distance and curvature is the reciprocal of that radius, so the curvature falls.
- 5
Explain why the curvature added by a given thin lens is the same wherever the object is placed.
Model answer
The curvature added depends only on the shape of the lens surfaces and its refractive index, neither of which changes when the object moves.
- 6
Explain in terms of the speed of light why a converging lens curves a wave-front inwards.
Model answer
Light travels more slowly in glass, and the lens is thickest at its centre, so the middle of the wave-front is delayed most and the emerging wave-front bulges inwards.
What is inside Levo
Six ways to work the same material.
Imaging and Signalling revision questions
- What does Imaging and Signalling cover in OCR A-Level Physics B?
- 12 subtopics: real images and the curvature of wave-fronts, lens power and focal length, the thin lens equation and the cartesian convention, linear magnification, measuring the power and focal length of a converging lens, images as arrays of numbers, bits, bytes and the information in an image, enhancing a digital image, wave-forms, frequency and wave speed, sampling and digitising an analogue signal, noise, resolution and digital transmission and polarisation of electromagnetic waves. Each one has its own page with questions and model answers.
- How is Imaging and Signalling organised?
- By the OCR H557 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Imaging and Signalling, 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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