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, 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 its conservationWork 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 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 raysProducing and receiving radio wavesAbsorption, transmission, refraction and reflectionInvestigating reflection and refraction of light
Forces
The spring constant, and work done in stretching
- 2 things to know
- Paper 11 (Physics)
Overview
What the spring constant measures and its unit, force = spring constant × extension with calculations and stiffness comparisons, work done in stretching as stored energy, work done = ½ × spring constant × extension², the area under a force-extension graph, and the effect of doubling the extension.
What you need to know
Answer each one before you reveal it.
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Key term
State the unit of the spring constant.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by the spring constant of a spring?
Model answer
The force needed to produce each metre of extension, which is a measure of how stiff the spring is.
- 2
State the unit of the spring constant.
Model answer
Newtons per metre (N/m).
- 3
Write, in words, the relationship between the force applied to a spring, its spring constant and its extension.
Model answer
Force = spring constant × extension.
- 4
Why must the extension, rather than the total stretched length, be used when finding a spring constant?
Model answer
The spring constant relates the force only to the increase in length, so the unstretched length has to be subtracted first.
- 5
A force of 12 N stretches a spring by 0.30 m. Calculate the spring constant.
Model answer
40 N/m, because 12 N ÷ 0.30 m = 40 N/m.
- 6
A force of 2.0 N stretches a spring by 4.0 cm. Calculate the spring constant.
Model answer
50 N/m, because 4.0 cm is 0.040 m and 2.0 N ÷ 0.040 m = 50 N/m.
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