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
Electricity
- 10 subtopics
- 30 things to know
- Paper 3
What Electricity covers
Electricity is examined in Physics A Paper 3. It covers charge, and producing static electricity; transfer of electrons, and electric fields; current as a rate of flow of charge; charge, current and time; series and parallel circuits, and circuit symbols; current, potential difference and resistance; resistors whose resistance changes, and investigating them; linear and non-linear circuit elements from graphs; net resistance in series and parallel; and circuits for measurement, and electrical power.
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 10 subtopics
Each one has its own page.
- Charge, and producing static electricityPositive and negative charge in all matter, zero net charge and the sign of an object that gains or loses electrons, the coulomb, producing static by rubbing, attraction and repulsion without contact, why insulators hold charge, and sparks, car-door shocks and earthing a fuel tanker.Open →
- Transfer of electrons, and electric fieldsWhich particles move when insulators are rubbed, why polythene and acetate rods charge oppositely, why the two charges are equal and opposite, and how an electric field explains forces between charged objects.Open →
- Current as a rate of flow of chargeCurrent as the rate of flow of charge, the electrons that carry it in a metal, the two conditions for charge to flow, the ampere and the ammeter, conventional current, and why the current is the same at every point in a single loop and is not used up in a lamp.Open →
- Charge, current and timeThe relationship between charge, current and time, the units of each, worked examples finding charge, current or time, and how charge compares for two components carrying different currents.Open →
- Series and parallel circuits, and circuit symbolsHow charge travels in series and parallel circuits, connecting ammeters and voltmeters, how potential difference and current are shared between components and branches, and the symbols for cells, batteries, fixed and variable resistors, lamps, diodes, light dependent resistors, thermistors, meters and switches.Open →
- Current, potential difference and resistancePotential difference as energy transferred per coulomb, the volt, the ohm and what resistance means, how current responds to changes in potential difference and resistance, and calculations with potential difference = current × resistance, including why current is proportional to potential difference when resistance is constant.Open →
- Resistors whose resistance changes, and investigating themWhat constant resistance means, why a filament lamp and a heated wire resist more, how diodes, thermistors and light dependent resistors behave, and circuits for investigating each of them.Open →
- Linear and non-linear circuit elements from graphsStraight and curved graphs of current against potential difference, finding resistance from readings and from a graph, the characteristic graphs of a fixed resistor, a filament lamp and a diode, resistance graphs for a thermistor and a light dependent resistor, and plotting results with y = mx + c and a line of best fit.Open →
- Net resistance in series and parallelHow adding a resistor in the same loop or on a new branch changes net resistance, what that does to lamp brightness and current, and calculations of net resistance and potential difference.Open →
- Circuits for measurement, and electrical powerA circuit for testing whether resistance is constant, why ammeters need low and voltmeters high resistance, thermistor and diode test circuits, and calculations linking power, potential difference, current and energy.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Compare the current against potential difference graphs of a fixed resistor and a filament lamp, and explain their shapes.
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Why is the current the same all round a single loop, and what happens to it when a bigger resistor is fitted?
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Why do protons not move from one surface to the other when two objects are rubbed together?
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State the relationship between quantity of charge, current and time.
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Two identical resistors are joined in one loop with a 6 V supply. What is the potential difference across each?
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What is meant by the potential difference between two points in a circuit?
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Why does the resistance of a filament lamp increase as the current through it increases?
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Is the net resistance of two resistors on separate branches larger or smaller than the smaller of the two resistances?
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Describe a circuit that could be used to monitor the temperature of a room.
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Which particles inside an atom carry negative charge, and which carry positive charge?
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A polythene rod is rubbed with a cloth and becomes negatively charged. Explain what has happened.
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What is electric current?
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What are the units of charge, current and time in the relationship connecting them?
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Two lamps are on separate branches across a 6 V supply. What is the potential difference across each lamp?
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What does a potential difference of 1 V mean in terms of energy and charge?
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Explain, in terms of the particles in a metal, why heating a wire raises its resistance.
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What shape is the graph of current against potential difference for a linear circuit element?
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Why does the current supplied by a cell increase when more branches are added across it?
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How can a simple circuit be used to check which way round a diode has been connected?
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Is charge found only in special materials, or in all matter?
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An acetate rod is rubbed with a cloth and becomes positively charged. Explain what has happened.
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Which particles flow to make a current in a metal wire?
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A current of 3 A flows for 20 s. How much charge passes?
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A cell supplies two branches, one carrying 0.4 A and the other 0.6 A. What current comes out of the cell?
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What is the unit of potential difference, and which instrument measures it?
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Why does a metal wire keep a steady resistance when only a small current is passed through it?
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Why does a straight line through the origin on a current against potential difference graph show that the resistance is constant?
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Two 12 Ω resistors on separate branches across a 6 V supply take a total current of 1.0 A. What is their net resistance?
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State the relationship between the power transferred by a circuit device, the potential difference across it and the current through it.
Take Electricity further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Current vs Potential difference
Current: the rate of flow of electric charge. Potential difference: the energy transferred per coulomb of charge between two points.
Series circuit vs Parallel circuit
Series circuit: one loop in which all the charge follows the same path. Parallel circuit: separate branches between which the charge divides.
Ammeter vs Voltmeter
Ammeter: instrument placed in the loop to measure current. Voltmeter: instrument connected across a component to measure potential difference.
Questions from this topic
Each one with the model answer underneath.
- 1
Which property of matter exists in a positive form and a negative form?
Model answer
Electric charge.
- 2
Which particles inside an atom carry negative charge, and which carry positive charge?
Model answer
Electrons carry negative charge and protons carry positive charge.
- 3
Is charge found only in special materials, or in all matter?
Model answer
All matter contains charge, because every atom contains positively charged protons and negatively charged electrons.
- 4
What is meant by saying that an object has zero net charge?
Model answer
The total positive charge on the object is equal to the total negative charge, so the two cancel out.
- 5
Why do most everyday objects have no overall charge?
Model answer
They contain equal numbers of positive and negative charges.
- 6
An object has more electrons than protons. What is the sign of its overall charge?
Model answer
Negative, because the negative charge is no longer balanced by the positive charge.
What is inside Levo
Six ways to work the same material.
Electricity revision questions
- What does Electricity cover in OCR GCSE Physics A?
- 10 subtopics: charge, and producing static electricity, transfer of electrons, and electric fields, current as a rate of flow of charge, charge, current and time, series and parallel circuits, and circuit symbols, current, potential difference and resistance, resistors whose resistance changes, and investigating them, linear and non-linear circuit elements from graphs, net resistance in series and parallel and circuits for measurement, and electrical power. Each one has its own page with questions and model answers.
- How is Electricity organised?
- By the OCR J249 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Electricity, 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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