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, 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
Matter
Compressing a gas, and changing its volume
- 3 things to know
- Paper 1
Overview
What happens to a gas when the pressure on it rises or falls, why gases compress easily, how volume and pressure are linked at constant temperature, and why a crisp bag swells uphill.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What happens to the pressure of a gas when it is compressed into a smaller space at a constant temperature?
Key term
A sealed bag of crisps swells as it is carried up a mountain. Explain why.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to a gas when the pressure applied to it is increased?
Model answer
It is compressed into a smaller volume.
- 2
Why can a gas be compressed easily when a liquid or a solid cannot?
Model answer
The molecules of a gas are far apart with large gaps between them, so they can be pushed much closer together.
- 3
In which direction does the pressure of a gas produce a force on a surface?
Model answer
It produces a net force at right angles to the surface.
- 4
What happens to a gas if the pressure applied to it is reduced?
Model answer
It expands to fill a larger volume.
- 5
What happens to the pressure of a gas when it is compressed into a smaller space at a constant temperature?
Model answer
The pressure increases, because the same number of molecules hit each unit area of the container more often.
- 6
A sealed bag of crisps swells as it is carried up a mountain. Explain why.
Model answer
The air pressure outside falls with height while the gas inside keeps pushing outwards, so the gas expands.
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