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
Radioactivity
Contamination and irradiation, and reducing the hazard
- 3 things to know
- Paper 12 (Physics)
Overview
The difference between irradiation and contamination, why irradiating an object does not make it radioactive, why contamination is the more serious long-term hazard, why alpha is most dangerous inside the body and gamma outside it, and how shielding, distance, time and careful handling reduce the risk.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is meant by radioactive contamination?
Key term
Why is contamination usually the more serious long-term hazard?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by irradiation?
Model answer
Irradiation is being exposed to radiation from a source that stays outside the object or person.
- 2
What is meant by radioactive contamination?
Model answer
Contamination is unwanted radioactive material getting onto or inside an object or a person.
- 3
Does irradiating an object make that object radioactive?
Model answer
No, once the source is taken away or shielded the irradiation stops and nothing radioactive is left behind.
- 4
Why is contamination usually the more serious long-term hazard?
Model answer
The radioactive material stays in contact with the person and keeps emitting radiation until it is removed or has decayed.
- 5
Why is an alpha source far more dangerous swallowed than held at arm's length?
Model answer
From outside, alpha particles cannot even get through skin, but inside the body they ionise the surrounding cells very heavily.
- 6
Why is a gamma source the greater hazard when it is outside the body?
Model answer
Gamma radiation is very penetrating, so it passes through skin and reaches organs deep inside.
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