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
Waves in Matter
Ray diagrams for reflection and refraction
- 3 things to know
- Paper 4
Overview
How convex and concave lenses refract parallel rays, focal length, lenses for long and short sight, the law of reflection and the normal, the path of a ray through a glass block, and investigating reflection and refraction with a ray box, including the spectrum from a prism.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State the law of reflection.
Key term
What is meant by the normal at a surface?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does a convex lens do to rays of light arriving parallel to its axis?
Model answer
It brings them together at the focal point on the far side of the lens.
- 2
What does a concave lens do to rays of light arriving parallel to its axis?
Model answer
It spreads them out, so they appear to have come from a point on the near side of the lens.
- 3
How does the shape of a convex lens differ from that of a concave lens?
Model answer
A convex lens is thicker in the middle than at its edges, while a concave lens is thinner in the middle than at its edges.
- 4
What is meant by the focal length of a lens?
Model answer
The distance from the centre of the lens to the point where rays parallel to the axis are brought together, or appear to spread from.
- 5
Which kind of lens is used to correct long sight, and why?
Model answer
A convex lens, because it converges the light before it enters the eye so the image forms on the retina instead of behind it.
- 6
Which kind of lens is used to correct short sight, and why?
Model answer
A concave lens, because it spreads the light before it enters the eye so the image forms on the retina instead of in front of it.
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