Key term
OCR GCSE Physics A J249
Electricity
Topic overviewCharge, and producing static electricityTransfer of electrons, and electric fieldsCurrent as a rate of flow of chargeCharge, current and timeSeries and parallel circuits, and circuit symbolsCurrent, potential difference and resistanceResistors whose resistance changes, and investigating themLinear and non-linear circuit elements from graphsNet resistance in series and parallelCircuits for measurement, and electrical power
Energy
Topic overviewConservation of energy, and energy storesEnergy changes on heating, and calculating themEnergy of a moving body, a spring and a raised objectDissipation, and energy transfer in domestic devicesPower ratings, efficiency, and increasing itReducing unwanted energy transfer, and the rate of cooling
Forces
Topic overviewMeasuring distance and time, and calculating speedConverting units, and ratesVectors and scalars in motionDistance-time and velocity-time graphsAverage speed, and the equations of uniform motionHow objects interact, and forces as vectorsNewton's first lawResolving forces, and free body diagramsResultant forces, and balanced forcesNewton's second law, and inertiaMomentum, and force as a change in momentumWork done, and stored energyPower, and Newton's third lawCircular motion and changing velocityStretching, bending and compressing; elastic and plasticForce and extension, linear and non-linearThe spring constant, and work done in stretchingGravitational fields, weight and free fallCalculations with weight and gravitational field strengthTurning forces and the moment of a forceLevers and gearsPressure in fluids, and the force on a surface
Global Challenges
Topic overviewTypical speeds and everyday accelerationsReaction time, stopping distance and the dangers of large decelerationsEstimating stopping distances and the forces in a collisionEnergy resources, and trends in their useThe national grid, and step-up and step-down transformersWhy the national grid is efficient, and the transformer equationMains electricity: a.c., d.c. and the domestic supplyLive, neutral and earth wires, and electrical dangerRed-shift and the Big BangThe formation of the Sun, and radiation from bodiesThe solar systemCircular orbits and stable orbitsRadiation and the temperature of a body, and seismic waves and sonar
Magnetism and Magnetic Fields
Topic overviewPermanent and induced magnets, and magnetic polesMagnetic fields, and the dipping compassThe magnetic effect of a current, and solenoidsThe motor effect and Fleming's left-hand ruleThe force on a conductor, and how a motor turnsInduced potential, alternators and dynamosTransformers and the turns ratioThe microphone
Matter
Topic overviewHow the atomic model changed, and the structure of the atomThe size of atoms, and defining densityDensity of the states of matter, and density calculationsConservation of mass in changes of stateHeating a system, and specific heat capacityCalculations with specific heat capacity and latent heatGas molecules, temperature and pressureCompressing a gas, and changing its volumeDoing work on a gasAtmospheric pressure and why it varies with heightFloating, sinking and pressure in a liquid
Radioactivity
Topic overviewProtons, neutrons and isotopesUnstable nuclei and the emissions they give outBalancing nuclear equationsElectron energy levels, and radiation from atomsHalf-life and the randomness of decayPenetration of alpha, beta and gammaContamination and irradiation, and half-life as a hazardUses of nuclear radiationNuclear fission and fusion
Waves in Matter
Topic overviewAmplitude, wavelength, frequency and periodThe wave equationTransverse and longitudinal wavesSound crossing a boundary; reflection, transmission and absorptionConverting sound to vibrations, and the range of hearingModelling waves with ripples and soundElectromagnetic waves as transverse, and energy transferFrequency and wavelength across the spectrumWhat our eyes detect, and light as an electromagnetic waveUses of electromagnetic wavesHazards of ultraviolet, X-rays and gamma raysExploring structures with waves, and producing radio wavesAbsorption, transmission, refraction and reflectionRay diagrams for reflection and refractionHow colour arises
Global Challenges
- 13 subtopics
- 39 things to know
- Paper 4
What Global Challenges covers
Global Challenges is examined in Physics A Paper 4. It covers typical speeds and everyday accelerations; reaction time, stopping distance and the dangers of large decelerations; estimating stopping distances and the forces in a collision; energy resources, and trends in their use; the national grid, and step-up and step-down transformers; why the national grid is efficient, and the transformer equation; mains electricity: a.c., d.c. and the domestic supply; live, neutral and earth wires, and electrical danger; red-shift and the Big Bang; the formation of the Sun, and radiation from bodies; the solar system; circular orbits and stable orbits; and radiation and the temperature of a body, and seismic waves and sonar.
Where it is assessed
Paper 4
Physics A Paper 4: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 13 subtopics
Each one has its own page.
- Typical speeds and everyday accelerationsTypical speeds for walking, running, cycling, sound, wind, cars, trains and aeroplanes, what an acceleration in m/s² means, estimating the accelerations of cars, sprinters, cyclists and buses, and converting kilometres per hour, kilometres, tonnes and minutes for speed calculations.Open →
- Reaction time, stopping distance and the dangers of large decelerationsTypical reaction times, measuring them by ruler drop or computer and what lengthens them, thinking and braking distance and what increases each, why large decelerations injure and how crumple zones, seat belts and air bags help, overheated brakes and skids, and handling reaction-time data with averages, histograms, scatter diagrams and sampling.Open →
- Estimating stopping distances and the forces in a collisionEstimated stopping distances at typical speeds, how thinking and braking distance change when speed doubles and why, calculating overall stopping and thinking distances, estimating the braking, driving and collision forces on cars, lorries and passengers, and why collision forces are so much larger than in ordinary driving.Open →
- Energy resources, and trends in their useRenewable and non-renewable resources, how wind, hydroelectricity, tides, the Sun and biofuel are used, what energy resources are used for, trends in coal, gas, nuclear and renewables and the reasons behind them, and ethical questions about nuclear waste, dams and wind farms that science alone cannot settle.Open →
- The national grid, and step-up and step-down transformersWhat the national grid is, the potential differences used for transmission and for homes, what substations do, and where step-up and step-down transformers sit and which coil has more turns.Open →
- Why the national grid is efficient, and the transformer equationWhy a high potential difference cuts the energy wasted in cables, how loss depends on current, why thick cables help, the turns ratio equation with calculations, and the power relationship for an ideal transformer.Open →
- Mains electricity: a.c., d.c. and the domestic supplyThe UK mains supply as alternating current at 50 Hz and about 230 V, the length of one cycle, why the mains is dangerous, direct supplies from cells and adapters, how direct and alternating potential differences and their traces differ, and why a transformer needs an alternating supply.Open →
- Live, neutral and earth wires, and electrical dangerWhat the live, neutral and earth wires do, the potential differences between them and their colours, why a live wire is dangerous even with the switch open, how insulation, double insulation, the earth wire and a fuse protect the user, and why wet hands raise the danger.Open →
- Red-shift and the Big BangWhat red-shift is and what it shows about galaxies moving away, why greater distance means greater red-shift and an expanding universe, the Big Bang model, the cosmic microwave background and other supporting evidence, and why the model stays open to change.Open →
- The formation of the Sun, and radiation from bodiesHow a collapsing cloud of dust and gas formed the Sun, what fusion needs and does, why a star stays stable, how stars end, and how emitted radiation depends on temperature.Open →
- The solar systemThe eight planets in order and how the inner and outer planets differ, the gravity that holds them in orbit, minor planets, asteroids and comets, natural and artificial satellites and how they compare, and what geostationary and polar orbits are used for.Open →
- Circular orbits and stable orbitsWhere gravity acts on an orbiting body, why a circular orbit has constant speed but changing velocity, why the Sun does no work on a planet, and how orbital speed and radius are linked.Open →
- Radiation and the temperature of a body, and seismic waves and sonarHow the balance of absorbed and emitted radiation sets the temperature of a road, a white surface and the Earth, how the atmosphere affects incoming and outgoing radiation, P and S seismic waves and what they reveal about the Earth's core, and finding the depth of water by sonar.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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What drives the turbines in a tidal scheme, how is the Sun used directly, and why are tides predictable and biofuel renewable?
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Give three reasons, including public concern, why renewable resources are used more, and explain why coal has been cut back faster than natural gas.
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Describe the ruler drop method for measuring reaction time, how the distance becomes a time, and why the catcher must not be warned.
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Why did the collapsing cloud of dust and gas become extremely hot?
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Describe a polar orbit and what it is used for.
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What is the difference between speed and velocity for an orbiting planet?
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What are typical cruising speeds for a train and for a passenger aeroplane?
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Explain why braking distance grows so much faster than speed.
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What is the national grid?
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Why does transferring power at a high potential difference make the grid efficient?
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What does a mains frequency of 50 Hz mean?
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What is the potential difference between the neutral wire and earth?
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What happens to the observed frequency of light from a galaxy that is moving away from us?
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What decides whether the temperature of a body rises, falls or stays the same?
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What does an acceleration of 2 m/s² mean in words?
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A driver's reaction time is 0.7 s and the car is travelling at 20 m/s. Estimate the thinking distance.
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Why are many power stations connected to one network rather than each supplying its own area?
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What happens to the energy that is wasted in transmission cables?
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How long does one cycle of the UK mains supply last?
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What are the insulation colours of the live, neutral and earth wires?
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What happens to the observed wavelength of light from a galaxy that is moving away from us?
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What was the Sun formed from?
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Name the eight planets of the solar system in order outwards from the Sun.
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In which direction does the gravitational force act on a body in a circular orbit?
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What determines the overall temperature of the Earth?
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A car pulls away from rest and reaches 12 m/s in 6 s. Estimate its acceleration.
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Describe the ruler drop method of measuring reaction time.
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A car of mass 1000 kg decelerates at 8 m/s². Estimate the braking force acting on it.
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What is the difference between a renewable and a non-renewable energy resource?
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In the national grid, which type of transformer is used at the power station and which is used near homes?
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How does the energy wasted in a cable depend on the current in it?
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Why is the mains supply dangerous to touch?
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Which mains wire is connected to the metal case of an appliance, and why?
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What is actually observed in the spectrum of a distant galaxy that shows it is red-shifted?
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What conditions were needed before fusion reactions could begin in the young Sun?
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How do the four inner planets differ from the four outer ones?
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What provides the force needed to keep a planet moving in a circle?
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How does the atmosphere affect the radiation from the Sun that passes through it?
Take Global Challenges further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Thinking distance vs Braking distance
Thinking distance: how far a vehicle travels while the driver reacts to a hazard. Braking distance: how far a vehicle travels from the brakes being applied until it stops.
Step-up transformer vs Step-down transformer
Step-up transformer: device whose secondary coil has more turns, raising the potential difference. Step-down transformer: device whose secondary coil has fewer turns, lowering the potential difference.
Live wire vs Neutral wire
Live wire: conductor carrying the alternating potential difference from the supply, at about 230 V. Neutral wire: conductor completing the circuit back to the supply, held near 0 V.
Questions from this topic
Each one with the model answer underneath.
- 1
What is a typical walking speed for an adult?
Model answer
About 1.5 m/s.
- 2
What is a typical running speed for a person?
Model answer
About 3 m/s.
- 3
What is a typical cycling speed?
Model answer
About 6 m/s.
- 4
What is a typical speed of sound in air?
Model answer
About 330 m/s.
- 5
Why can no single typical value be quoted for wind speed?
Model answer
Wind speed varies greatly with the weather, the place and the height above the ground, from a light breeze of a few m/s to over 20 m/s in a storm.
- 6
What is a typical speed for a car in a built-up area, and on a motorway?
Model answer
About 13 m/s in a built-up area and about 30 m/s on a motorway.
What is inside Levo
Six ways to work the same material.
Global Challenges revision questions
- What does Global Challenges cover in OCR GCSE Physics A?
- 13 subtopics: typical speeds and everyday accelerations, reaction time, stopping distance and the dangers of large decelerations, estimating stopping distances and the forces in a collision, energy resources, and trends in their use, the national grid, and step-up and step-down transformers, why the national grid is efficient, and the transformer equation, mains electricity: a.c., d.c. and the domestic supply, live, neutral and earth wires, and electrical danger, red-shift and the big bang, the formation of the sun, and radiation from bodies, the solar system, circular orbits and stable orbits and radiation and the temperature of a body, and seismic waves and sonar. Each one has its own page with questions and model answers.
- How is Global Challenges organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Global Challenges, 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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