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
Energy
Dissipation, and energy transfer in domestic devices
- 3 things to know
- Paper 2
Overview
What dissipation means and why dissipated energy is hard to use again, examples from gearboxes, cables, loudspeakers, phones and braking bicycles, and the useful and wasted transfers in torches, drills, fans, heaters and hairdryers powered by batteries or the mains.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Give an example of energy being dissipated in the wires of an electrical circuit.
Key term
What happens to the energy carried away by the sound waves from a loudspeaker?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by the dissipation of energy?
Model answer
Energy spreading out into the surroundings, where it is stored in ways that are no longer useful.
- 2
Why is dissipated energy so difficult to make use of again?
Model answer
It has been spread thinly through a large amount of matter at close to the temperature of the surroundings.
- 3
Give an example of energy being dissipated by friction in a machine.
Model answer
The moving parts of a gearbox rub together and energy is transferred to the thermal store of the metal and the oil around it.
- 4
Give an example of energy being dissipated in the wires of an electrical circuit.
Model answer
Current in a connecting cable warms the cable, so energy is transferred to the thermal store of the wire and the air around it.
- 5
What happens to the energy carried away by the sound waves from a loudspeaker?
Model answer
The waves are absorbed by the room and the air, and the energy ends up in their thermal stores.
- 6
Does dissipation of energy break the law of conservation of energy?
Model answer
No, the total energy is unchanged; the energy has only been transferred to less useful stores.
Other ways to work this
The same content, four other ways.
What is inside Levo
Six ways to work the same material.
Every question in Energy, 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.
Or £46 a year, about £3.83 a month. Cancel anytime.