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 national grid, and step-up and step-down transformers
- 3 things to know
- Paper 2
Overview
What the national grid is, the potential differences used for transmission and for homes, what substations do, and where step-up and step-down transformers sit and which coil has more turns.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Why are many power stations connected to one network rather than each supplying its own area?
Key term
In the national grid, which type of transformer is used at the power station and which is used near homes?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the national grid?
Model answer
The network of cables, pylons and transformers that carries electrical power from power stations to homes, schools and businesses across the country.
- 2
At what sort of potential difference is power carried away from a power station across the country?
Model answer
At a very high potential difference, typically hundreds of thousands of volts.
- 3
What happens to the potential difference before electricity reaches houses?
Model answer
It is reduced in stages at substations until it is at the much lower value used in homes.
- 4
Why is a much lower potential difference used for the local supply to homes?
Model answer
A very high potential difference would be far too dangerous in houses, so it is lowered to a value that appliances can use safely.
- 5
Where in the grid is the potential difference highest?
Model answer
In the long transmission cables between the power station and the local substations.
- 6
What is a substation used for?
Model answer
It houses transformers that lower the potential difference so the electricity can be distributed locally.
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