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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, and calculating efficiencyReducing 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 lawNewton's second lawForce and the time taken to change velocityWork done, and stored energyPower, and Newton's third lawStretching, 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 power in a transformerMains 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 system
Magnetism and Magnetic Fields
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 volumeAtmospheric pressure and why it varies with height
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 absorptionModelling 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 raysRay diagrams for reflection and refractionHow colour arises
Energy
- 6 subtopics
- 18 things to know
- Paper 2
What Energy covers
Energy is examined in Physics A Paper 2. It covers conservation of energy, and energy stores; energy changes on heating, and calculating them; energy of a moving body, a spring and a raised object; dissipation, and energy transfer in domestic devices; power ratings, and calculating efficiency; and reducing unwanted energy transfer, and the rate of cooling.
Where it is assessed
Paper 2
Physics A Paper 2: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 6 subtopics
Each one has its own page.
- Conservation of energy, and energy storesThe law of conservation of energy, what a closed system is, why dissipated energy is not lost, and the store changes for thrown stones, braking cars, kettles and freewheeling cyclists.Open →
- Energy changes on heating, and calculating themWhat heating does to the thermal store of a system, specific heat capacity and why water warms slowly, work done by a force against friction and in a heater filament, and calculations of work done, energy transferred electrically, energy to change temperature, and kilowatt-hours and their cost.Open →
- Energy of a moving body, a spring and a raised objectThe equations for the kinetic, gravitational potential and elastic potential stores, with calculations for moving cars and balls, lifted crates, falling masses and stretched springs.Open →
- Dissipation, and energy transfer in domestic devicesWhat dissipation means and why dissipated energy is hard to use again, examples from gearboxes, cables, loudspeakers, phones and braking bicycles, and the useful and wasted transfers in torches, drills, fans, heaters and hairdryers powered by batteries or the mains.Open →
- Power ratings, and calculating efficiencyPower as energy transferred each second, what a power rating means, calculations of energy, power and time, why a low-power appliance left on all day can cost more than a high-power one used briefly, and calculating efficiency from energies or powers, including why it can never exceed 100 per cent.Open →
- Reducing unwanted energy transfer, and the rate of coolingHow wall thickness and thermal conductivity decide how fast a building cools, cavity wall and loft insulation, double glazing and draught excluders, how lubricating a bicycle chain or noisy bearings cuts wasted energy, and the surface area of a hot water tank.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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Give the two ways of calculating efficiency, from energies and from powers, and explain why efficiency can never exceed 100 per cent.
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What is an appliance's power, in watts, how is power found, and what does a 2500 W kettle do compared with a 60 W lamp?
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What does the law of conservation of energy state?
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State the equation for the energy in the kinetic store of a moving object.
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What is meant by the dissipation of energy?
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Which two properties of a building's walls affect how quickly it cools down?
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What is meant by a closed system when energy transfers are being considered?
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What is meant by the specific heat capacity of a substance?
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State the equation for the energy in the gravitational potential store of an object raised above the ground.
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Give an example of energy being dissipated in the wires of an electrical circuit.
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What is meant by the thermal conductivity of a material?
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Why is it more accurate to say that energy has been dissipated than to say it has been lost?
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Two blocks of equal mass but different materials are given the same amount of energy. Which one reaches the higher temperature?
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State the equation for the energy stored in a stretched spring.
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What happens to the energy carried away by the sound waves from a loudspeaker?
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What is meant by the power of an appliance?
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How does the rate of cooling of a building change if its walls are built from a material of higher thermal conductivity?
Take Energy further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Thermal conductivity vs Specific heat capacity
Thermal conductivity: measure of how readily energy is conducted through a material. Specific heat capacity: energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Power vs Efficiency
Power: energy transferred each second, measured in watts. Efficiency: useful energy output as a fraction of the total energy supplied.
Lubrication vs Thermal insulation
Lubrication: applying oil or grease so two surfaces slide more easily. Thermal insulation: surrounding something with a poor conductor to slow energy transfer.
Questions from this topic
Each one with the model answer underneath.
- 1
What does the law of conservation of energy state?
Model answer
Energy cannot be created or destroyed; it can only be transferred from one store to another or dissipated to the surroundings.
- 2
What is meant by a closed system when energy transfers are being considered?
Model answer
A system that exchanges no energy with anything outside it, so its total energy stays the same.
- 3
Energy is transferred between several stores inside a closed system. What has happened to the total energy of that system?
Model answer
There is no net change, so the total energy afterwards is equal to the total energy before.
- 4
A rubber ball is dropped and each bounce reaches a lower height than the last. Has energy been destroyed?
Model answer
No, energy has been transferred to the thermal stores of the ball, the floor and the air, so the total energy is unchanged.
- 5
Why is it more accurate to say that energy has been dissipated than to say it has been lost?
Model answer
The energy still exists, but it has spread out into the surroundings where it is no longer useful.
- 6
A toy car is given a push along a bench and eventually stops. Account for its energy as a closed system.
Model answer
The energy in its kinetic store has been transferred to the thermal stores of the car, the bench and the air, so the total is unchanged.
What is inside Levo
Six ways to work the same material.
Energy revision questions
- What does Energy cover in OCR GCSE Physics A?
- 6 subtopics: conservation of energy, and energy stores, energy changes on heating, and calculating them, energy of a moving body, a spring and a raised object, dissipation, and energy transfer in domestic devices, power ratings, and calculating efficiency and reducing unwanted energy transfer, and the rate of cooling. Each one has its own page with questions and model answers.
- How is Energy organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Energy, 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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