How can a uniformly charged sphere be modelled when considering points outside the sphere?

It can be modelled as a point charge located at its centre.

State the definition of electric field strength.

Electric field strength is the force per unit positive charge.

Write the equation that defines electric field strength in terms of force and charge, and identify each symbol.

E = F/q, where E is electric field strength, F is the force on the charge, and q is the positive charge experiencing the force.

What mathematical relationship do both gravitational and electric fields from point sources share?

Both follow an inverse square law for field strength.

OCR A-Level Physics A H556

Practical Skills in the Written Papers

Topic overview Planning an experiment Implementing and recording Processing and interpreting data Plotting and interpreting graphs Evaluating results and procedures Mathematical skills and notation

The Practical Endorsement

Topic overview Analogue and digital measuring instruments Improving accuracy with repeat timing, fiducial markers and plumb lines Timing, calipers and micrometers Constructing and testing circuits Signal generators and oscilloscopes Generating and measuring waves Data loggers, modelling software and ionising radiation

Physical Quantities and Units

Topic overview Physical quantities, estimation and unit conversions S.I. base and derived units Prefixes, homogeneity and labelling conventions

Making Measurements and Analysing Data

Topic overview Systematic and random errors Precision, accuracy and uncertainties

Nature of Quantities

Topic overview Scalars and vectors Adding and resolving vectors

Motion

Topic overview Displacement, speed, velocity and acceleration Motion graphs and the equations of motion Measuring g and investigating motion experimentally Free fall, reaction time and stopping distance Projectile motion

Forces in Action

Topic overview Newton's second law and weight Drag and the factors affecting it Terminal velocity Moments, couples and equilibrium Density, pressure and upthrust

Work, Energy and Power

Topic overview Work done and conservation of energy Kinetic and gravitational potential energy Power and efficiency

Materials

Topic overview Hooke's law and springs Force-extension graphs and work done Elastic potential energy, stress and strain The Young modulus Stress-strain graphs and material behaviour

Newton’s Laws of Motion and Momentum

Topic overview Newton's three laws and linear momentum Force as rate of change of momentum Impulse and force-time graphs Conservation of momentum and collisions

Charge and Current

Topic overview Electric current and the coulomb Elementary charge, charge carriers and Kirchhoff's first law Mean drift velocity

Energy, Power and Resistance

Topic overview Circuit symbols and diagrams Potential difference and e.m.f.Energy transfer in circuits Ohm's law and I-V characteristics Filament lamps, diodes, thermistors and LDRs Resistivity and how it is measured How resistivity varies with temperature Electrical power and the kilowatt-hour

Electrical Circuits

Topic overview Kirchhoff's laws and combining resistances E.m.f., internal resistance and lost volts Potential dividers

Waves

Topic overview Progressive waves and their properties The wave equation Reflection, refraction and diffraction Wave graphs and intensity The electromagnetic spectrum Polarisation Refraction and refractive index Critical angle and total internal reflection The principle of superposition Interference, coherence and path difference Two-source interference, Young's double-slit experiment and the diffraction grating Forming stationary waves Stationary waves on strings and in air columns Measuring the speed of sound Node spacing, amplitude and phase in stationary waves Harmonics and the fundamental mode

Quantum Physics

Topic overview Photons, electronvolts and the Planck constant from LEDs Demonstrating the photoelectric effect Work function and Einstein's equation Electron diffraction The de Broglie equation

Thermal Physics

Topic overview Thermal equilibrium and absolute temperature The kinetic model of solids, liquids and gases Brownian motion and internal energy Specific heat capacity Measuring specific heat capacity Specific latent heat Measuring specific latent heat Moles, the Avogadro constant and kinetic theory Gas laws, the ideal gas equation and r.m.s. speed Maxwell-Boltzmann distribution, Boltzmann constant and internal energy

Circular Motion

Topic overview Radians, angular velocity and period Centripetal force and acceleration

Oscillations

Topic overview Describing simple harmonic motion The defining equation of simple harmonic motion and timing oscillations Velocity, period and graphical relationships Energy in a simple harmonic oscillator Damping, forced oscillations and resonance

Gravitational Fields

Topic overview Gravitational fields and field strength Newton's law of gravitation Field strength of a point mass and the uniform field near Earth Kepler's laws and orbital motion Orbital period and geostationary orbits Gravitational potential Gravitational potential energy and escape velocity

Astrophysics and Cosmology

Topic overview The solar system and the birth of a star The death of a low-mass star Supernovae, neutron stars and black holes The Hertzsprung-Russell diagram Energy levels and emission spectra Absorption spectra and spectral lines Photon energy and the diffraction grating Wien's law and Stefan's law Astronomical distances, parallax and the cosmological principle Doppler shift and Hubble's law The expanding universe and the Big Bang Evidence for the Big Bang and dark energy

Capacitors

Topic overview Capacitance and charging a capacitor Capacitors in series Capacitors in parallel and combined circuits Energy stored by a capacitor Charging and discharging through a resistor Investigating capacitor discharge The time constant Iterative modelling, exponential decay and the constant-ratio property

Electric Fields

Topic overview Electric fields and field lines Coulomb's law and electric field strength Uniform fields, parallel plates and permittivity Electric potential Electric potential energy and capacitance of a sphere

Electromagnetism

Topic overview Magnetic fields and field patterns Fleming's left-hand rule and the motor effect Magnetic flux density and the tesla Charged particles in magnetic fields Magnetic flux, flux linkage and Faraday's law Transformers and the a.c. generator

Nuclear and Particle Physics

Topic overview Alpha-particle scattering and the nuclear model Proton number, nucleon number and isotopes The strong nuclear force and nuclear radius Particles, antiparticles and hadrons Leptons and the quark model Quark composition and charges Beta decay in the quark model Radioactive decay and the three radiations Nuclear decay equations Activity, decay constant and half-life Exponential decay and radioactive dating Mass-energy equivalence Annihilation, mass defect and binding energy Binding energy per nucleon and induced fission The fission reactor and nuclear waste Nuclear fusion and balancing nuclear equations

Medical Imaging

Topic overview The X-ray tube X-ray attenuation and imaging CAT scanning Medical tracers and the gamma camera PET scanning Ultrasound and the piezoelectric transducer Acoustic impedance and reflection Doppler ultrasound

Electric Fields

5 subtopics
15 things to know
Papers 1, 2 and 3

What Electric Fields covers

The electric field: Coulomb's law and field strength, the uniform field between parallel plates, and electric potential and potential energy.

Where it is assessed

Papers 1, 2 and 3

Newtonian world, astrophysics and particles, drawn on across the papers.

Check the OCR specification ↗

The 5 subtopics

Each one has its own page.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Define electric field strength, state what electric field lines show, and state how a uniformly charged sphere can be modelled for points outside it.

Numbers

How does the capacitance equation for a parallel plate capacitor change when a dielectric is inserted, and how is the permittivity of the dielectric related to relative permittivity?

Numbers

How does electric potential vary with distance from a point charge, and where is it defined as zero?

Numbers

State the capacitance of an isolated conducting sphere, and the two equations used to derive it.

Key term

What property determines gravitational field strength, and what property determines electric field strength?

Evaluation

State the relationship between electric field strength, potential difference, and plate separation in a uniform electric field.

Key term

What produces electric fields?

Key term

When using Coulomb's law to calculate force, what quantities must you know?

Key term

Where is electric potential defined as zero?

Key term

What is the starting equation for deriving the capacitance of an isolated sphere?

Key term

What do electric field lines represent and in which direction do they point?

Key term

Name the types of field that give rise to forces.

Evaluation

Write the equation for uniform electric field strength between parallel plates and define each symbol.

Key term

Write the equation for electric potential at distance r from a point charge Q and identify each term.

Key term

Which definition of capacitance is used when deriving the capacitance of an isolated sphere?

Take Electric Fields further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

Electric field strength vs Electric potential
Electric field strength: force per unit positive charge. Electric potential: work done per unit positive charge in bringing a small test charge from infinity to that point.
Electric potential energy vs Electric field strength
Electric potential energy: the product of the charge and the electric potential. Electric field strength: force per unit positive charge.
Uniform electric field vs Radial electric field
Uniform electric field: field between parallel plates whose strength equals potential difference divided by plate separation. Radial electric field: field around a point charge whose strength follows an inverse square law with distance.

Questions from this topic

Each one with the model answer underneath.

1
What produces electric fields?
Model answer
Electric charges produce electric fields.
2
How can a uniformly charged sphere be modelled when considering points outside the sphere?
Model answer
It can be modelled as a point charge located at its centre.
3
What do electric field lines represent and in which direction do they point?
Model answer
Electric field lines map electric fields and show the direction of force that would act on a positive test charge.
4
State the definition of electric field strength.
Model answer
Electric field strength is the force per unit positive charge.
5
Write the equation that defines electric field strength in terms of force and charge, and identify each symbol.
Model answer
E = F/q, where E is electric field strength, F is the force on the charge, and q is the positive charge experiencing the force.
6
What mathematical relationship do both gravitational and electric fields from point sources share?
Model answer
Both follow an inverse square law for field strength.

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Electric Fields revision questions

What does Electric Fields cover in OCR A-Level Physics A?: 5 subtopics: electric fields and field lines, coulomb's law and electric field strength, uniform fields, parallel plates and permittivity, electric potential and electric potential energy and capacitance of a sphere. Each one has its own page with questions and model answers.
How is Electric Fields organised?: By the OCR H556 specification, subtopic by subtopic, so it matches the order you are taught it in.

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