Evaluation
CCEA A-Level Physics 1210
Physical Quantities, Scalars and Vectors
Moments and Equilibrium
Linear Motion and Dynamics
Newton's Laws of Motion
Linear Momentum and Impulse
Work, Energy and Power
Current, Charge and Potential Difference
Resistance and Resistivity
Topic overviewResistance and Ohm's lawOhmic and non-ohmic behaviourResistors in series and in parallelInvestigating current, voltage and resistance in series and parallel circuitsElectrical power and energy in resistive circuitsResistivity and the equation R = ρl/AMeasuring the resistivity of a metalCurrent–voltage characteristics of a conductor, a lamp and a diodeResistance, temperature and superconductivity
Internal Resistance and Potential Dividers
Topic overviewInternal resistance and terminal potential differenceConsequences of internal resistance for external circuitsMeasuring electromotive force and internal resistanceThe potential divider and variable outputPotential dividers in lighting and heating control circuitsLoaded potential dividers and output voltage calculations
Waves
Refraction
Lenses
Superposition, Interference and Diffraction
Topic overviewSuperposition of wavesStanding waves, nodes and antinodesStanding waves on stretched stringsStanding waves in a pipe closed at one endMeasuring the speed of sound with a resonance tubeConditions for observable interferencePath difference and phase differenceYoung's double slitDiffraction at a single slitThe diffraction grating
Quantum Physics
Wave-Particle Duality
Astronomy
Practical Skills and Data Analysis
Topic overviewChoosing and using measuring instrumentsPrecision, accuracy and recording measurementsUsing the cathode ray oscilloscope to measure voltage and frequencyTables, graphs and presenting resultsLinearising a relationship and using the gradientAbsolute and percentage uncertaintyCombining uncertainties and uncertainty on a graphRandom and systematic error, reliability and refining an experiment
Deformation of Solids
Thermal Physics
Topic overviewBoyle's law, Charles's law and the pressure lawThe ideal gas equation pV = nRTThe Avogadro constant, the mole and pV = NkTInternal energy and the distribution of molecular energyThe kinetic theory equation pV = ⅓Nm⟨c²⟩Average molecular kinetic energy and temperatureAbsolute zero and the kelvin scaleSpecific heat capacity and the electrical method
Uniform Circular Motion
Simple Harmonic Motion
Topic overviewDefining simple harmonic motion and a = −ω²xDisplacement, velocity and acceleration: x = A cos ωtThe simple pendulum and T = 2π√(l/g)The loaded spiral spring and T = 2π√(m/k)SHM graphs and finding velocity from a gradientFree vibrations, forced vibrations and resonanceDamping: light, critical and over-damping
The Nucleus and Radioactive Decay
Topic overviewAlpha-particle scattering and the nuclear atomNuclear radius and nucleon numberThe density of nuclear matterAlpha, beta and gamma radiation: nature, penetration and rangeNuclear equations and changes in nucleon and proton numberThe random and exponential nature of radioactive decayActivity, the decay constant and A = −λNExponential decay calculations with A = A₀e^(−λt)Half-life and measuring it
Nuclear Energy, Fission and Fusion
Gravitational Fields
Electric Fields
Capacitors
Magnetic Fields
Charged Particles and Accelerators
Electric Fields
The field of a point charge
- 3 things to know
- Unit A2 2
Overview
Recall questions on E = kq/r² and its derivation from Coulomb's law, why the test charge cancels, worked field-strength calculations, the shape of the E against r graph and what to plot for a straight line, locating the neutral point between two charges, adding fields as vectors, and why the field inside a hollow conductor is zero.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Derive the equation for the electric field strength of a point charge from Coulomb's law
Key term
Why does the test charge not appear in the equation for the field strength of a point charge?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Give the equation for the electric field strength due to a point charge and define each symbol.
Model answer
E = q/(4πε₀r²), or equivalently E = kq/r², where E is the field strength in N C⁻¹, q the charge in coulombs and r the distance from it in metres.
- 2
Derive that equation from Coulomb's law.
Model answer
The force on a test charge q₀ at distance r is F = qq₀/(4πε₀r²), and field strength is F/q₀, so dividing by q₀ gives E = q/(4πε₀r²).
- 3
Why does the test charge not appear in the result?
Model answer
Field strength is force per unit charge, so the test charge cancels and the field depends only on the charge producing it and the distance.
- 4
Calculate the field strength 0.20 m from a point charge of 5.0 nC.
Model answer
E = 8.99 × 10⁹ × 5.0 × 10⁻⁹ ÷ 0.20², which is 45.0 ÷ 0.040, giving 1.1 × 10³ N C⁻¹.
- 5
Check that field strength by finding the force on a 1.0 nC test charge placed there.
Model answer
F = qE = 1.0 × 10⁻⁹ × 1.1 × 10³ = 1.1 × 10⁻⁶ N, which is also what Coulomb's law gives for the two charges 0.20 m apart.
- 6
What shape is a graph of field strength against distance from a point charge?
Model answer
A curve falling steeply at first and then flattening, following an inverse square relationship and approaching but never reaching zero.
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