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
Red-shift and the Big Bang
- 3 things to know
- Paper 2
Overview
What red-shift is and what it shows about galaxies moving away, why greater distance means greater red-shift and an expanding universe, the Big Bang model, the cosmic microwave background and other supporting evidence, and why the model stays open to change.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What happens to the observed wavelength of light from a galaxy that is moving away from us?
Key term
What is actually observed in the spectrum of a distant galaxy that shows it is red-shifted?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by the red-shift of light from a galaxy?
Model answer
The light arrives with a longer wavelength than it was emitted with, so its features are shifted towards the red end of the spectrum.
- 2
What happens to the observed frequency of light from a galaxy that is moving away from us?
Model answer
The observed frequency is lower than the frequency at which the light was emitted.
- 3
What happens to the observed wavelength of light from a galaxy that is moving away from us?
Model answer
The observed wavelength is longer than the wavelength at which the light was emitted.
- 4
What is actually observed in the spectrum of a distant galaxy that shows it is red-shifted?
Model answer
The dark lines in its spectrum appear at longer wavelengths than the same lines measured from a source in a laboratory.
- 5
What does a red-shift tell us about how a galaxy is moving?
Model answer
It is receding, moving away from us.
- 6
How does the red-shift of a galaxy depend on its distance from us?
Model answer
The more distant a galaxy is, the greater its red-shift, so the faster it is receding.
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