Key term
AQA GCSE Combined Science Physics 8464
Atomic Structure
Topic overviewThe structure of an atomMass number, atomic number and isotopesFrom the plum pudding model to the nuclear modelChadwick, the neutron, and comparing the modelsRadioactive decay and nuclear radiationNuclear equationsHalf-lives and the random nature of radioactive decayRadioactive contamination
Electricity
Topic overviewCircuit symbols, electrical charge and currentCurrent, resistance and potential differenceOhmic conductors, filament lamps, diodes and thermistorsLight-dependent resistors, and investigating resistanceCurrent and potential difference in series and parallelConstructing circuits, and calculating in series circuitsDirect and alternating potential difference, and mains electricityPower and efficiencyAppliances, and the energy transferred by electrical workPower, and the power ratings of domestic appliancesThe National Grid
Energy
Forces
Topic overviewScalars, vectors, forces and the resultant forceGravityWork done and energy transferStretching, compressing, and the spring constantLinear and non-linear extension, and work done on a springDistance, displacement and speedThe speed of sound, and the distance-speed-time equationVelocity and the distance-time relationshipAcceleration, deceleration and velocity-time graphsArea under a velocity-time graph, and the uniform acceleration equationNewton's First LawNewton's Second and Third LawsStopping distance and reaction timeFactors affecting braking distanceBraking force, deceleration and the dangers of stopping quickly
Magnetism and Electromagnetism
Particle Model of Matter
Electricity
Power and efficiency
- 3 things to know
- Physics Paper 1
Overview
Efficiency in terms of energy transfer and of power with calculations, and power in terms of potential difference and current and in terms of current and resistance as P = I²R, with the units each equation uses.
What you need to know
Answer each one before you reveal it.
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Key term
State the equation for efficiency in terms of energy transfer.
Numbers
A motor is supplied with 800 J and transfers 200 J usefully. Calculate its efficiency.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does the efficiency of a device tell you?
Model answer
What share of the energy supplied to it is transferred usefully.
- 2
State the equation for efficiency in terms of energy transfer.
Model answer
Efficiency = useful output energy transfer ÷ total input energy transfer.
- 3
A motor is supplied with 800 J and transfers 200 J usefully. Calculate its efficiency.
Model answer
Efficiency = 200 ÷ 800 = 0.25, which is 25%.
- 4
State the equation for efficiency in terms of power.
Model answer
Efficiency = useful power output ÷ total power input.
- 5
A lamp has a power input of 60 W and gives out 9 W of light. Calculate its efficiency as a percentage.
Model answer
Efficiency = 9 ÷ 60 = 0.15, which is 15%.
- 6
On which two electrical quantities does the power transferred by a circuit device depend?
Model answer
The potential difference across it and the current through it.
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