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
- 8 subtopics
- 23 things to know
- Paper 12 (Physics)
What Global Challenges covers
Global Challenges is examined in Paper 12 (Physics). It covers typical speeds and everyday accelerations; reaction time, stopping distance and the dangers of large decelerations; stopping distance, acceleration and collision force calculations; energy resources, and trends in their use; the national grid, and step-up and step-down transformers; why the national grid is efficient, and power in a transformer; mains electricity: a.c., d.c. and the domestic supply; and live, neutral and earth wires, and electrical danger.
Where it is assessed
Paper 12 (Physics)
Combined Science A, Paper 12 (Physics): 1 hour 10 minutes, 60 marks, 16.7% of the qualification.
Check the OCR specification ↗The 8 subtopics
Each one has its own page.
- Typical speeds and everyday accelerationsTypical speeds for walking, running, cycling, sound, wind, cars, trains and aeroplanes, what an acceleration in m/s² means, estimating the accelerations of cars, sprinters, cyclists and buses, and converting kilometres per hour, kilometres, tonnes and minutes for speed calculations.Open →
- Reaction time, stopping distance and the dangers of large decelerationsTypical reaction times, measuring them by ruler drop or computer and what lengthens them, thinking and braking distance and what increases each, why large decelerations injure and how crumple zones, seat belts and air bags help, overheated brakes and skids, and handling reaction-time data with averages, histograms, scatter diagrams and sampling.Open →
- Stopping distance, acceleration and collision force calculationsAdding thinking and braking distance to find a stopping distance, estimating thinking distance from speed and reaction time, estimating the accelerations and decelerations of cars, the resultant forces on an accelerating car and motorcycle and on a car in a crash, and why collision forces are so much larger than in ordinary driving.Open →
- Energy resources, and trends in their useRenewable and non-renewable resources, how wind, hydroelectricity, tides, the Sun and biofuel are used, what energy resources are used for, trends in coal, gas, nuclear and renewables and the reasons behind them, and ethical questions about nuclear waste, dams and wind farms that science alone cannot settle.Open →
- The national grid, and step-up and step-down transformersWhat 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.Open →
- Why the national grid is efficient, and power in a transformerWhy power = potential difference × current means a higher potential difference needs a smaller current, how the energy wasted in cables depends on the square of that current, why thick cables and one shared network help, and equal power in and out of an ideal transformer, with calculations.Open →
- Mains electricity: a.c., d.c. and the domestic supplyThe 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.Open →
- Live, neutral and earth wires, and electrical dangerWhat the live, neutral and earth wires do, the potential differences between them and their colours, why a live wire is dangerous even with the switch open, how insulation, double insulation, the earth wire and a fuse protect the user, and why wet hands raise the danger.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What drives the turbines in a tidal scheme, how is the Sun used directly, and why are tides predictable and biofuel renewable?
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Give three reasons, including public concern, why renewable resources are used more, and explain why coal has been cut back faster than natural gas.
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Describe the ruler drop method for measuring reaction time, how the distance becomes a time, and why the catcher must not be warned.
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What are typical cruising speeds for a train and for a passenger aeroplane?
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What is the national grid?
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Why does transferring power at a high potential difference make the grid efficient?
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What does a mains frequency of 50 Hz mean?
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What is the potential difference between the neutral wire and earth?
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What does an acceleration of 2 m/s² mean in words?
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Why are many power stations connected to one network rather than each supplying its own area?
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What happens to the energy that is wasted in transmission cables?
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How long does one cycle of the UK mains supply last?
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What are the insulation colours of the live, neutral and earth wires?
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A car pulls away from rest and reaches 12 m/s in 6 s. Estimate its acceleration.
Key term
Describe the ruler drop method of measuring reaction time.
Process
A driver's reaction time is 0.7 s and the car is travelling at 20 m/s. Estimate the thinking distance.
Process
Why are the forces in a collision so much larger than the forces in ordinary driving?
Key term
What is the difference between a renewable and a non-renewable energy resource?
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In the national grid, which type of transformer is used at the power station and which is used near homes?
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How does the energy wasted in a cable depend on the current in it?
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Why is the mains supply dangerous to touch?
Key term
Which mains wire is connected to the metal case of an appliance, and why?
Take Global Challenges further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Thinking distance vs Braking distance
Thinking distance: how far a vehicle travels while the driver reacts to a hazard. Braking distance: how far a vehicle travels from the brakes being applied until it stops.
Step-up transformer vs Step-down transformer
Step-up transformer: device whose secondary coil has more turns, raising the potential difference. Step-down transformer: device whose secondary coil has fewer turns, lowering the potential difference.
Live wire vs Neutral wire
Live wire: conductor carrying the alternating potential difference from the supply, at about 230 V. Neutral wire: conductor completing the circuit back to the supply, held near 0 V.
Questions from this topic
Each one with the model answer underneath.
- 1
What is a typical walking speed for an adult?
Model answer
About 1.5 m/s.
- 2
What is a typical running speed for a person?
Model answer
About 3 m/s.
- 3
What is a typical cycling speed?
Model answer
About 6 m/s.
- 4
What is a typical speed of sound in air?
Model answer
About 330 m/s.
- 5
Why can no single typical value be quoted for wind speed?
Model answer
Wind speed varies greatly with the weather, the place and the height above the ground, from a light breeze of a few m/s to over 20 m/s in a storm.
- 6
What is a typical speed for a car in a built-up area, and on a motorway?
Model answer
About 13 m/s in a built-up area and about 30 m/s on a motorway.
What is inside Levo
Six ways to work the same material.
Global Challenges revision questions
- What does Global Challenges cover in OCR GCSE Combined Science Physics?
- 8 subtopics: typical speeds and everyday accelerations, reaction time, stopping distance and the dangers of large decelerations, stopping distance, acceleration and collision force calculations, energy resources, and trends in their use, the national grid, and step-up and step-down transformers, why the national grid is efficient, and power in a transformer, mains electricity: a.c., d.c. and the domestic supply and live, neutral and earth wires, and electrical danger. Each one has its own page with questions and model answers.
- How is Global Challenges organised?
- By the OCR J250 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Global Challenges, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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