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
Global Challenges
The formation of the Sun, and radiation from bodies
- 3 things to know
- Paper 2
Overview
How 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.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What was the Sun formed from?
Key term
What conditions were needed before fusion reactions could begin in the young Sun?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What was the Sun formed from?
Model answer
A large cloud of dust and gas that was pulled together by gravity.
- 2
Why did the collapsing cloud of dust and gas become extremely hot?
Model answer
Gravity pulled the material inwards and squeezed it together, and the particles moved faster as they fell in, so the temperature and pressure at the centre rose enormously.
- 3
What conditions were needed before fusion reactions could begin in the young Sun?
Model answer
The temperature and pressure in the core had to become high enough for hydrogen nuclei to collide and join together.
- 4
What happens in a fusion reaction in a star?
Model answer
Light nuclei such as hydrogen join to form heavier nuclei such as helium, releasing a very large amount of energy.
- 5
Explain why the Sun stays the same size for billions of years.
Model answer
The outward push caused by the energy released in fusion balances the inward pull of gravity, so the star is in equilibrium and neither collapses nor expands.
- 6
What are the stages in the life of a star before it becomes stable?
Model answer
A cloud of dust and gas is pulled together by gravity to form a protostar, which heats until fusion starts and it becomes a main sequence star.
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