Key term
OCR GCSE Combined Science Physics J250
Electricity
Topic overviewCharge, and producing static electricityTransfer of electrons in charging and dischargingCurrent 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 its conservationWork 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 strength
Global Challenges
Topic overviewTypical speeds and everyday accelerationsReaction time, stopping distance and the dangers of large decelerationsStopping distance, acceleration and collision force calculationsEnergy 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 danger
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 pressure
Radioactivity
Waves in Matter
Topic overviewAmplitude, wavelength, frequency and periodThe wave equationTransverse and longitudinal wavesModelling 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 raysProducing and receiving radio wavesAbsorption, transmission, refraction and reflectionInvestigating reflection and refraction of light
Global Challenges
Mains electricity: a.c., d.c. and the domestic supply
- 3 things to know
- Paper 12 (Physics)
Overview
The UK mains supply as alternating current at 50 Hz and about 230 V, the length of one cycle, why the mains is dangerous, direct supplies from cells and adapters, how direct and alternating potential differences and their traces differ, and why a transformer needs an alternating supply.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
How long does one cycle of the UK mains supply last?
Key term
Why is the mains supply dangerous to touch?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Is the domestic mains supply in the UK direct or alternating current?
Model answer
It is alternating current.
- 2
What is the frequency of the UK domestic mains supply?
Model answer
50 Hz.
- 3
What is the potential difference of the UK domestic mains supply?
Model answer
About 230 V.
- 4
What does a mains frequency of 50 Hz mean?
Model answer
The supply goes through 50 complete cycles every second, so the current changes direction 100 times each second.
- 5
How long does one cycle of the UK mains supply last?
Model answer
0.02 s, because one second is shared between 50 cycles.
- 6
Why is the mains supply dangerous to touch?
Model answer
About 230 V is large enough to drive a current through a person that can stop the heart or cause burns.
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