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
Forces
Measuring distance and time, and calculating speed
- 3 things to know
- Paper 1
Overview
Instruments for measuring length and time, why light gates beat a hand-held stopwatch, how reaction time is reduced, and finding speed from distance, time and the gradient of a distance-time graph.
What you need to know
Answer each one before you reveal it.
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Key term
How could you measure the distance around a running track without laying a rule end to end along it?
Key term
How do light gates give a more trustworthy time than a stopwatch pressed by hand?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which instrument would you choose to measure the length of a laboratory bench, and to what precision can it be read?
Model answer
A metre rule or a tape measure, read to the nearest millimetre.
- 2
How could you measure the distance around a running track without laying a rule end to end along it?
Model answer
Use a trundle wheel, which counts complete turns of a wheel of known circumference.
- 3
Why is a hand-operated stopwatch unreliable for timing a very short event?
Model answer
Human reaction time adds an uncertainty of roughly 0.2 s at the start and again at the stop, which is a large fraction of a short interval.
- 4
How do light gates give a more trustworthy time than a stopwatch pressed by hand?
Model answer
The timer starts and stops electronically as the object breaks each beam, so no human reaction time is involved.
- 5
How would you reduce the effect of reaction time when timing a swinging pendulum?
Model answer
Time twenty complete swings and divide the total time by twenty.
- 6
Describe how you would measure the distance travelled by a toy car along a bench and the time it takes, using simple equipment.
Model answer
Mark a start line and a finish line, measure between them with a metre rule, and time the run between the marks with a stopwatch.
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