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
Magnetism and Magnetic Fields
- 8 subtopics
- 24 things to know
- Paper 3
What Magnetism and Magnetic Fields covers
Magnetism and Magnetic Fields is examined in Physics A Paper 3. It covers permanent and induced magnets, and magnetic poles; magnetic fields, and the dipping compass; the magnetic effect of a current, and solenoids; the motor effect and Fleming's left-hand rule; the force on a conductor, and how a motor turns; induced potential, alternators and dynamos; transformers and the turns ratio; and the microphone.
Where it is assessed
Paper 3
Physics A Paper 3: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 8 subtopics
Each one has its own page.
- Permanent and induced magnets, and magnetic polesAttraction and repulsion between poles as a non-contact force, the field lines between like and unlike poles and the neutral point, how the force weakens with distance, permanent and induced magnets, why induced magnetism only attracts, the magnetic metals, and why steel suits permanent magnets and iron suits electromagnets.Open →
- Magnetic fields, and the dipping compassWhat a magnetic field is, where it is strongest and how line spacing shows strength, field direction, plotting a field with a compass or iron filings, the dipping compass and what its dip shows about the field and core of the Earth, and why the magnetic pole in the far north behaves as a south pole.Open →
- The magnetic effect of a current, and solenoidsShowing that a current has a magnetic effect, the circular field around a straight wire and the right-hand grip rule, how current and distance change the field strength, the field inside and outside a solenoid, ways of making a solenoid stronger, and electromagnets.Open →
- The motor effect and Fleming's left-hand ruleThe force on a current-carrying wire in a magnetic field and the equal force on the magnet, how the angle to the field, the current and the field strength change the force, what reversing the current or field does, and Fleming's left-hand rule with worked directions.Open →
- The force on a conductor, and how a motor turnsForce = magnetic flux density × current × length, the tesla and the units needed, when the equation applies, calculations of force, flux density, current and length, why a coil turns in a field, reversing the current every half turn, and making a motor faster or reversing it.Open →
- Induced potential, alternators and dynamosElectromagnetic induction and ways to induce a potential difference, when a current flows and how its field opposes the change, making the induced potential difference larger, and how an alternator with slip rings and a dynamo with a split-ring commutator produce alternating and direct current.Open →
- Transformers and the turns ratioThe primary and secondary coils and the iron core, how a changing field transfers energy and why a transformer needs alternating current, step-up and step-down transformers, the turns ratio equation with calculations, stepping up for the grid, and power in and out of an ideal transformer.Open →
- The microphoneWhat a microphone does, which part the sound moves, the coil attached to the diaphragm, how the induced signal is produced, and how louder or higher-pitched sounds change it.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
What is a solenoid, why is the field stronger than a single wire's, how is the field strengthened, and why does an iron core help?
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In Fleming's left-hand rule, what do the first finger, the second finger and the thumb each represent?
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What is electromagnetic induction, how can a potential difference be induced in a coil, and why does pushing a magnet in take effort?
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In a dynamic microphone, what is attached to the diaphragm, how is a signal produced, and what changes when the sound is louder?
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What is meant by a magnetic field?
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Write the equation linking the force on a current-carrying conductor to the magnetic flux density, the current and the length of conductor.
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What are the two coils of a transformer called?
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State the rule that summarises the force between two magnetic poles.
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What does the spacing between magnetic field lines tell you about the field?
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Describe a simple demonstration showing that an electric current produces a magnetic effect.
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What is the motor effect?
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In the equation for the force on a conductor, what units must the current and the length be given in?
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What is electromagnetic induction?
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What are the primary and secondary coils of a transformer wound on?
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What is attached to the diaphragm of a dynamic microphone?
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Why is the force between two magnetic poles described as a non-contact force?
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What is the agreed direction of a magnetic field line?
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What happens to the direction of the magnetic field if the current in a wire is reversed?
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Explain why a current-carrying wire placed in a magnetic field experiences a force.
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Under what condition does the equation force = magnetic flux density × current × length apply?
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Give two ways of inducing a potential difference across a coil of wire.
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Why must the supply to a transformer be an alternating current?
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Explain how a dynamic microphone produces an electrical signal from a sound wave.
Take Magnetism and Magnetic Fields further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Permanent magnet vs Induced magnet
Permanent magnet: material that produces its own field all the time. Induced magnet: material that becomes magnetic only while it sits in a field.
Motor effect vs Electromagnetic induction
Motor effect: the force on a current-carrying conductor placed in a magnetic field. Electromagnetic induction: the potential difference produced across a conductor when the field around it changes.
Alternator vs Dynamo
Alternator: generator with slip rings giving alternating current. Dynamo: generator with a split-ring commutator giving direct current.
Questions from this topic
Each one with the model answer underneath.
- 1
What happens when the north pole of one bar magnet is brought close to the south pole of another?
Model answer
They attract each other.
- 2
What happens when the north poles of two bar magnets are brought close together?
Model answer
They repel each other.
- 3
State the rule that summarises the force between two magnetic poles.
Model answer
Like poles repel and unlike poles attract.
- 4
Why is the force between two magnetic poles described as a non-contact force?
Model answer
The magnets push or pull on each other without ever touching.
- 5
In which direction do the magnetic field lines outside a bar magnet run?
Model answer
They run from the north pole round to the south pole.
- 6
Describe the field lines in the gap when a north pole and a south pole are placed facing each other.
Model answer
They run straight across the gap from the north pole to the south pole, linking the two magnets together.
What is inside Levo
Six ways to work the same material.
Magnetism and Magnetic Fields revision questions
- What does Magnetism and Magnetic Fields cover in OCR GCSE Physics A?
- 8 subtopics: permanent and induced magnets, and magnetic poles, magnetic fields, and the dipping compass, the magnetic effect of a current, and solenoids, the motor effect and fleming's left-hand rule, the force on a conductor, and how a motor turns, induced potential, alternators and dynamos, transformers and the turns ratio and the microphone. Each one has its own page with questions and model answers.
- How is Magnetism and Magnetic Fields organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Magnetism and Magnetic Fields, 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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