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
Magnetism and Magnetic Fields
The force on a conductor, and how a motor turns
- 3 things to know
- Paper 11 (Physics)
Overview
Force = magnetic flux density × current × length, the tesla and the units needed, when the equation applies, calculations of force, flux density, current and length, why a coil turns in a field, reversing the current every half turn, and making a motor faster or reversing it.
What you need to know
Answer each one before you reveal it.
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Key term
In the equation for the force on a conductor, what units must the current and the length be given in?
Key term
Under what condition does the equation force = magnetic flux density × current × length apply?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Write the equation linking the force on a current-carrying conductor to the magnetic flux density, the current and the length of conductor.
Model answer
Force = magnetic flux density × current × length.
- 2
What is magnetic flux density, and in what unit is it measured?
Model answer
It is a measure of the strength of a magnetic field, measured in tesla (T).
- 3
In the equation for the force on a conductor, what units must the current and the length be given in?
Model answer
The current in amperes (A) and the length in metres (m), which give the force in newtons (N).
- 4
Under what condition does the equation force = magnetic flux density × current × length apply?
Model answer
Only when the conductor lies at right angles to the magnetic field.
- 5
A wire of length 0.25 m carries a current of 3 A at right angles to a field of magnetic flux density 0.4 T. Calculate the force on the wire.
Model answer
The force is 0.3 N.
- 6
A 0.05 m length of wire carrying a current of 4 A at right angles to a field feels a force of 0.6 N. Calculate the magnetic flux density.
Model answer
The magnetic flux density is 3 T.
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