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
Electricity
Transfer of electrons in charging and discharging
- 3 things to know
- Paper 11 (Physics)
Overview
Which particles move when insulators are rubbed and why protons stay put, how polythene and acetate rods charge oppositely, why the charges on the rod and the cloth are equal and opposite, why rubbing works where resting does not, and how a charged sphere discharges through a person to earth.
What you need to know
Answer each one before you reveal it.
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Key term
A polythene rod is rubbed with a cloth and becomes negatively charged. Explain what has happened.
Key term
An acetate rod is rubbed with a cloth and becomes positively charged. Explain what has happened.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which charged particles move when two insulating surfaces are rubbed together?
Model answer
Electrons.
- 2
Why do protons not move from one surface to the other when two objects are rubbed together?
Model answer
Protons are held tightly in the nuclei of the atoms and are not free to move.
- 3
A polythene rod is rubbed with a cloth and becomes negatively charged. Explain what has happened.
Model answer
Electrons have been transferred from the cloth onto the rod, giving the rod more electrons than protons.
- 4
An acetate rod is rubbed with a cloth and becomes positively charged. Explain what has happened.
Model answer
Electrons have been transferred from the rod onto the cloth, leaving the rod with fewer electrons than protons.
- 5
A cloth is used to charge a rod negatively. What charge is left on the cloth?
Model answer
An equal positive charge.
- 6
Why are the charges on the two objects always equal in size and opposite in sign after rubbing?
Model answer
No charge is created or destroyed; the electrons one object gains are exactly the electrons the other object loses.
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