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
Waves in Matter
Modelling waves with ripples and sound
- 3 things to know
- Paper 2
Overview
Why ripples model transverse waves and sound longitudinal ones, methods for measuring the speed of ripples and of sound, and the evidence that waves transfer energy without moving matter along.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Roughly how does the speed of sound in air compare with the speed of ripples on water?
Key term
Explain why ripples on water are used as a model of a transverse wave.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Explain why ripples on water are used as a model of a transverse wave.
Model answer
The water surface moves up and down while the ripple travels sideways, so the vibration is at right angles to the direction of travel.
- 2
Why is sound in air described as a longitudinal wave?
Model answer
The air moves backwards and forwards along the direction the wave travels, forming compressions and rarefactions.
- 3
Describe a way of measuring the speed of ripples by timing them.
Model answer
Time how long a single ripple takes to cross a measured distance in the tank, then divide the distance by the time.
- 4
Describe a way of finding the speed of ripples using the wave equation.
Model answer
Count the number of ripples produced each second and measure the distance between crests, then multiply the frequency by the wavelength.
- 5
Describe how the speed of sound in air can be measured outdoors over a long distance.
Model answer
Stand a measured distance from someone making a sharp sound, time the gap between seeing the sound being made and hearing it, then divide the distance by the time.
- 6
Describe how two microphones and a timer can be used to measure the speed of sound in a laboratory.
Model answer
Place the microphones a measured distance apart in line with the source and record the time between the sound reaching each one, then divide the separation by that time.
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