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
Resistance and Resistivity
Resistors in series and in parallel
- 3 things to know
- Unit AS 1
Overview
Equation for the total resistance of resistors connected in series, equation for the total resistance of resistors connected in parallel and why resistances simply add when resistors are connected in series.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State the equation for the total resistance of resistors connected in series.
Key term
State the equation for the total resistance of resistors connected in parallel.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the equation for the total resistance of resistors connected in series.
Model answer
The total resistance is R = R₁ + R₂ + R₃ + …, where each R is the resistance of one of the resistors in ohms.
- 2
State the equation for the total resistance of resistors connected in parallel.
Model answer
The total resistance R satisfies 1/R = 1/R₁ + 1/R₂ + 1/R₃ + …, so the reciprocal of the total is the sum of the reciprocals of the separate resistances.
- 3
Explain why resistances simply add when resistors are connected in series.
Model answer
The same current passes through each resistor, and the potential differences add to give the total, so dividing the total potential difference by the common current gives the sum of the individual resistances.
- 4
Explain why the total resistance of a parallel combination is always less than the smallest individual resistance.
Model answer
Each resistor has the full potential difference across it, so adding another branch provides an extra path for charge and increases the total current for the same potential difference, which means the total resistance must fall.
- 5
Calculate the total resistance of a 4.7 kΩ, a 2.2 kΩ and a 1.0 kΩ resistor connected in series.
Model answer
The total is 4.7 + 2.2 + 1.0 = 7.9 kΩ, and subtracting the 2.2 kΩ and 1.0 kΩ from 7.9 kΩ returns the 4.7 kΩ as a check.
- 6
Calculate the total resistance of a 6.0 Ω and a 3.0 Ω resistor connected in parallel.
Model answer
1/R = 1/6.0 + 1/3.0 = 0.500 Ω⁻¹, so R = 2.0 Ω, and 1/2.0 = 0.500 Ω⁻¹, confirming the result.
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