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, 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 lawWork 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 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 raysInvestigating reflection and refraction of light
Global Challenges
Reaction time, stopping distance and the dangers of large decelerations
- 3 things to know
- Paper 6 (Physics)
Overview
Typical 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.
What you need to know
Answer each one before you reveal it.
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Key term
Describe the ruler drop method for measuring reaction time, how the distance becomes a time, and why the catcher must not be warned.
Key term
Describe the ruler drop method of measuring reaction time.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the typical range of human reaction times?
Model answer
Between about 0.2 s and 0.9 s.
- 2
Describe the ruler drop method of measuring reaction time.
Model answer
One person holds a ruler vertically between the open finger and thumb of another and releases it without warning; the second person catches it as quickly as possible and the distance the ruler fell is read off.
- 3
In the ruler drop method, how is the measured distance turned into a reaction time?
Model answer
The distance fallen is converted using a prepared table or graph, because a longer fall corresponds to a longer time.
- 4
Why must the person catching the ruler not be told when it will be released?
Model answer
If they can anticipate the release they respond early, so the measurement is shorter than their true reaction time.
- 5
Why is the ruler drop test repeated several times and a mean taken?
Model answer
Individual results vary a lot, so a mean of repeats reduces the effect of random variation and gives a more reliable value.
- 6
Describe a computer-based method of measuring reaction time.
Model answer
The screen changes or a sound is made at a random moment and the person presses a key as fast as they can, with the computer timing the gap between the signal and the press.
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