Key term
OCR GCSE Physics A J249
Electricity
Topic overviewCharge, and producing static electricityTransfer of electrons, and electric fieldsCurrent 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 force as a change in momentumWork 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 strengthTurning forces and the moment of a forceLevers and gearsPressure in fluids, and the force on a surface
Global Challenges
Topic overviewTypical speeds and everyday accelerationsReaction time, stopping distance and the dangers of large decelerationsEstimating stopping distances and the forces in a collisionEnergy resources, and trends in their useThe national grid, and step-up and step-down transformersWhy the national grid is efficient, and the transformer equationMains electricity: a.c., d.c. and the domestic supplyLive, neutral and earth wires, and electrical dangerRed-shift and the Big BangThe formation of the Sun, and radiation from bodiesThe solar systemCircular orbits and stable orbitsRadiation and the temperature of a body, and seismic waves and sonar
Magnetism and Magnetic Fields
Topic overviewPermanent and induced magnets, and magnetic polesMagnetic fields, and the dipping compassThe magnetic effect of a current, and solenoidsThe motor effect and Fleming's left-hand ruleThe force on a conductor, and how a motor turnsInduced potential, alternators and dynamosTransformers and the turns ratioThe microphone
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 pressureCompressing a gas, and changing its volumeDoing work on a gasAtmospheric pressure and why it varies with heightFloating, sinking and pressure in a liquid
Radioactivity
Topic overviewProtons, neutrons and isotopesUnstable nuclei and the emissions they give outBalancing nuclear equationsElectron energy levels, and radiation from atomsHalf-life and the randomness of decayPenetration of alpha, beta and gammaContamination and irradiation, and half-life as a hazardUses of nuclear radiationNuclear fission and fusion
Waves in Matter
Topic overviewAmplitude, wavelength, frequency and periodThe wave equationTransverse and longitudinal wavesSound crossing a boundary; reflection, transmission and absorptionConverting sound to vibrations, and the range of hearingModelling 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 raysExploring structures with waves, and producing radio wavesAbsorption, transmission, refraction and reflectionRay diagrams for reflection and refractionHow colour arises
Radioactivity
- 9 subtopics
- 27 things to know
- Paper 4
What Radioactivity covers
Radioactivity is examined in Physics A Paper 4. It covers protons, neutrons and isotopes; unstable nuclei and the emissions they give out; balancing nuclear equations; electron energy levels, and radiation from atoms; half-life and the randomness of decay; penetration of alpha, beta and gamma; contamination and irradiation, and half-life as a hazard; uses of nuclear radiation; and nuclear fission and fusion.
Where it is assessed
Paper 4
Physics A Paper 4: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 9 subtopics
Each one has its own page.
- Protons, neutrons and isotopesThe particles in a nucleus and their charges and masses, what nucleons are, what an isotope is, and how mass number and atomic number give the neutron count and nuclear charge.Open →
- Unstable nuclei and the emissions they give outWhy unstable nuclei emit radiation, what alpha and beta particles, gamma rays and neutrons are and the charge each carries, and how the mass number and atomic number change with each emission, including why beta emission leaves the mass number unchanged.Open →
- Balancing nuclear equationsHow alpha, beta, gamma, neutrons and protons are written in decay equations, which totals must balance, and worked examples for radium, carbon, uranium, polonium and iodine decays.Open →
- Electron energy levels, and radiation from atomsElectrons in energy levels, excitation by absorbing radiation and emission on falling back, ionisation and the positive ion it leaves, the wide range of frequencies atoms and nuclei emit, gamma rays from the nucleus, the spectrum in order of frequency, and what sets the frequency emitted.Open →
- Half-life and the randomness of decayHalf-life in terms of nuclei and count rate, why decay is random yet a sample has a reliable half-life, finding a half-life from count rates and graphs, the net decline in activity as a ratio after several half-lives, activity calculations, and modelling decay with dice.Open →
- Penetration of alpha, beta and gammaWhat absorbs alpha, beta and gamma radiation, which is most and least penetrating, which ionises most strongly, how far each travels in air, and reading absorption tests.Open →
- Contamination and irradiation, and half-life as a hazardIrradiation and contamination and which is the greater long-term hazard, why alpha is most dangerous inside the body and gamma outside it, reducing exposure and avoiding contamination, and why sources with long or short half-lives are hazards in medicine, nuclear waste, spills and smoke alarms.Open →
- Uses of nuclear radiationMedical tracers, why gamma emitters suit them and alpha emitters do not, how a tracer is detected and used to check the thyroid, radiotherapy with external beams from several directions and with implanted sources, and why the dose must be controlled carefully.Open →
- Nuclear fission and fusionNuclear fission, the neutron that starts it and what it releases, chain reactions and how control rods keep them steady, uranium and plutonium fuels, fusion in stars and the mass converted to energy, why fusion needs extreme conditions, and how fission and fusion differ.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
Compare the penetration and ionising power of alpha, beta and gamma radiation, and state how far beta particles travel in air.
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Where do gamma rays come from, how does gamma frequency compare with visible light, and what is the order of the electromagnetic spectrum by frequency?
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In radiotherapy, why is the beam aimed from several directions, how is a source used inside the body, and why must the dose be controlled?
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Which two kinds of particle make up the nucleus of an atom?
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What is an alpha particle made of?
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Why is it impossible to say which nucleus in a sample will decay next?
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What is meant by irradiation?
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Apart from the two smaller nuclei, what else comes out of a fission event?
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What is the relative charge of a proton and what is the relative charge of a neutron?
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What is a beta particle?
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What mass number and atomic number are written for an alpha particle in a decay equation?
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What is meant by ionisation of an atom?
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What is meant by saying that radioactive decay is random?
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What thickness of material is enough to absorb alpha particles?
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What is meant by radioactive contamination?
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Why is a gamma emitter chosen as a tracer for looking at an organ?
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Name a fuel whose nuclei undergo fission in a reactor.
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Which count of particles in the nucleus gives an element its characteristic positive charge?
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Which of the emissions from an unstable nucleus carries neither charge nor mass?
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What mass number and atomic number are written for a beta particle in a decay equation?
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Which part of the electromagnetic spectrum is produced by changes in the nucleus itself?
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If individual decays cannot be predicted, why does a sample still have a reliable half-life?
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What material and thickness is needed to absorb beta particles?
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Why is contamination usually the more serious long-term hazard?
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How is the radiation from a tracer detected once it has been given to a patient?
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How is the energy released by fission carried away from the split nucleus?
Take Radioactivity further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Alpha particle vs Beta particle
Alpha particle: two protons and two neutrons, the same as a helium nucleus. Beta particle: a fast-moving electron thrown out of the nucleus.
Mass number vs Atomic number
Mass number: total count of protons and neutrons in a nucleus. Atomic number: count of protons in a nucleus, which identifies the element.
Irradiation vs Contamination
Irradiation: exposure to radiation from a source that stays outside the object. Contamination: unwanted radioactive material getting onto or inside an object.
Questions from this topic
Each one with the model answer underneath.
- 1
Which two kinds of particle make up the nucleus of an atom?
Model answer
The nucleus is made of protons and neutrons.
- 2
What is the relative charge of a proton and what is the relative charge of a neutron?
Model answer
A proton has a relative charge of +1 and a neutron has no charge at all.
- 3
Why does the nucleus of every atom carry a positive charge?
Model answer
It contains positively charged protons, and the neutrons alongside them are neutral, so the overall nuclear charge is positive.
- 4
Which count of particles in the nucleus gives an element its characteristic positive charge?
Model answer
The number of protons, because each proton contributes a charge of +1.
- 5
The nucleus of a boron atom carries a charge of +5. How many protons does it contain?
Model answer
It contains five protons.
- 6
What name is given to the protons and neutrons of a nucleus taken together?
Model answer
They are called nucleons.
What is inside Levo
Six ways to work the same material.
Radioactivity revision questions
- What does Radioactivity cover in OCR GCSE Physics A?
- 9 subtopics: protons, neutrons and isotopes, unstable nuclei and the emissions they give out, balancing nuclear equations, electron energy levels, and radiation from atoms, half-life and the randomness of decay, penetration of alpha, beta and gamma, contamination and irradiation, and half-life as a hazard, uses of nuclear radiation and nuclear fission and fusion. Each one has its own page with questions and model answers.
- How is Radioactivity organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Radioactivity, 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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