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, and calculating efficiencyReducing 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 lawNewton's second lawForce and the time taken to change velocityWork done, and stored energyPower, and Newton's third lawStretching, 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 power in a transformerMains 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 system
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 pressureCompressing a gas, and changing its volumeAtmospheric pressure and why it varies with height
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 absorptionModelling 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 raysRay diagrams for reflection and refractionHow colour arises
Electricity
Circuits for measurement, and electrical power
- 3 things to know
- Paper 1
Overview
A 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.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
How can a simple circuit be used to check which way round a diode has been connected?
Key term
State the relationship between the power transferred by a circuit device, the potential difference across it and the current through it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe a circuit that could be used to test whether the resistance of a component stays constant.
Model answer
Join a cell, an ammeter, a variable resistor and the component in one loop with a voltmeter across the component, then take pairs of current and potential difference readings as the variable resistor is changed.
- 2
Why should an ammeter have as low a resistance as possible?
Model answer
So that adding it to the circuit does not change the current it is there to measure.
- 3
Why should a voltmeter have as high a resistance as possible?
Model answer
So that almost no current passes through the voltmeter itself and the circuit it is connected across is left almost unchanged.
- 4
Describe a circuit that could be used to monitor the temperature of a room.
Model answer
Put a thermistor in a loop with a cell and a fixed resistor and connect a voltmeter across the thermistor; as the room warms the thermistor's resistance falls and the voltmeter reading changes.
- 5
How can a simple circuit be used to check which way round a diode has been connected?
Model answer
Include it in a loop with a cell, a protective resistor and an ammeter; a reading close to zero shows it is the way round that blocks the current.
- 6
Why is a variable resistor useful when a set of current and potential difference readings is being collected?
Model answer
It lets the current be changed in steps so that several pairs of readings can be taken from one circuit.
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