Key term
OCR GCSE Combined Science Physics J250
Electricity
Topic overviewCharge, and producing static electricityTransfer of electrons in charging and dischargingCurrent 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 lawWork 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 strength
Global Challenges
Topic overviewTypical speeds and everyday accelerationsReaction time, stopping distance and the dangers of large decelerationsStopping distance, acceleration and collision force calculationsEnergy 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 danger
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 pressure
Radioactivity
Waves in Matter
Topic overviewAmplitude, wavelength, frequency and periodThe wave equationTransverse and longitudinal wavesModelling 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 raysInvestigating reflection and refraction of light
Forces
Gravitational fields, weight and free fall
- 3 things to know
- Paper 5 (Physics)
Overview
Gravitational fields around every mass and why they only attract, field strength on the Earth and the Moon, weight as a force measured in newtons with a newtonmeter, how mass differs from weight, the centre of mass, and free fall at about 10 m/s² whatever the mass.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
Compare the gravitational field strength at the surface of the Moon with that at the surface of the Earth, and explain the difference.
Key term
State the unit in which weight is measured.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What surrounds every object that has mass?
Model answer
A gravitational field.
- 2
What effect does an object's gravitational field have on other masses?
Model answer
It attracts them, because gravitational forces are always attractive and never repulsive.
- 3
What decides how strong an object's gravitational field is?
Model answer
Its mass: the more massive the object, the stronger its field.
- 4
Explain why the gravitational field of a book is never noticed, even though the book has one.
Model answer
The mass of a book is tiny, so its field is far too weak for the pull it exerts on other objects to be detected.
- 5
Compare the gravitational field strength at the surface of the Moon with that at the surface of the Earth, and explain the difference.
Model answer
The Moon's field strength is much smaller because the Moon has far less mass than the Earth.
- 6
Can a gravitational field ever push two masses apart?
Model answer
No, gravitational fields only ever attract.
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