Key term
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
Capacitors
Charging and discharging a capacitor
- 3 things to know
- Unit A2 2
Overview
Experiment to demonstrate the charging of a capacitor, how the discharge of a capacitor is demonstrated and shape of a graph of current against time during charging.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Describe how the discharge of a capacitor is demonstrated.
Key term
Describe the shape of a graph of current against time during charging.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe an experiment to demonstrate the charging of a capacitor.
Model answer
A capacitor is connected in series with a resistor and a supply through a switch, and the current and the potential difference across the capacitor are recorded at intervals as the switch is closed.
- 2
Describe how the discharge of a capacitor is demonstrated.
Model answer
The charged capacitor is disconnected from the supply and connected across a resistor, and the falling potential difference or current is recorded at intervals.
- 3
Describe the shape of a graph of current against time during charging.
Model answer
The current starts at its maximum value and falls exponentially towards zero.
- 4
Describe the shape of a graph of potential difference across the capacitor against time during charging.
Model answer
It starts at zero and rises, steeply at first and then more slowly, approaching the supply voltage without ever quite reaching it.
- 5
Why is the charging current greatest at the instant the switch is closed?
Model answer
The capacitor is uncharged so there is no opposing potential difference across it, and the whole supply voltage is across the resistor.
- 6
Why does the charging current fall as the capacitor charges?
Model answer
The growing potential difference across the capacitor opposes the supply, leaving less across the resistor and so driving a smaller current.
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