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
Forces
Resultant forces, and balanced forces
- 2 things to know
- Paper 3
Overview
Finding the resultant of forces along one line, worked examples for rockets, trolleys, swimmers and lifts, what balanced forces mean, and why a zero resultant does not always mean rest.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
A swimmer whose weight is 600 N experiences an upthrust of 450 N. What is the size and direction of the resultant force on her?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How is the resultant of two forces acting along the same straight line found?
Model answer
Add them if they point the same way and subtract them if they point in opposite directions.
- 2
A rocket has a thrust of 2000 N upwards and a weight of 1400 N downwards. What is the size and direction of the resultant force on it?
Model answer
600 N upwards.
- 3
A trolley is pushed with 25 N forwards while friction resists with 4 N and air resistance with 1 N. What resultant force acts on it?
Model answer
20 N forwards.
- 4
One tug of war team pulls the rope with 900 N to the left while the other pulls with 850 N to the right. What is the resultant, and which way does the rope move?
Model answer
A resultant of 50 N to the left, so the rope moves to the left.
- 5
A swimmer whose weight is 600 N experiences an upthrust of 450 N. What is the size and direction of the resultant force on her?
Model answer
150 N downwards.
- 6
What does a resultant force do to an object that starts at rest?
Model answer
It makes the object begin to accelerate in the direction of the resultant.
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