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
Energy
Reducing unwanted energy transfer, and the rate of cooling
- 3 things to know
- Paper 12 (Physics)
Overview
How wall thickness and thermal conductivity decide how fast a building cools, cavity wall and loft insulation, double glazing and draught excluders, how lubricating a bicycle chain or noisy bearings cuts wasted energy, and the surface area of a hot water tank.
What you need to know
Answer each one before you reveal it.
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Key term
What is meant by the thermal conductivity of a material?
Key term
How does the rate of cooling of a building change if its walls are built from a material of higher thermal conductivity?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which two properties of a building's walls affect how quickly it cools down?
Model answer
The thickness of the walls and the thermal conductivity of the material they are made from.
- 2
What is meant by the thermal conductivity of a material?
Model answer
A measure of how readily energy is transferred through it by conduction.
- 3
How does increasing the thickness of a building's walls affect its rate of cooling?
Model answer
It lowers the rate of cooling, because energy has to be conducted through a greater thickness of material.
- 4
How does the rate of cooling of a building change if its walls are built from a material of higher thermal conductivity?
Model answer
The building cools more quickly, because energy is conducted out through the walls more readily.
- 5
Two identical houses are heated to the same temperature, but one has thicker walls of the same material. Which cools more slowly?
Model answer
The house with the thicker walls.
- 6
Two walls are the same thickness, one of brick and one of insulating foam. Which building cools more slowly?
Model answer
The one with foam walls, because foam has the lower thermal conductivity.
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