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
Electrical power and energy in resistive circuits
- 3 things to know
- Unit AS 1
Overview
Recall questions on P = VI and the derivations of P = I²R and P = V²/R, the factor of four when current doubles, calculating energy transferred over a time, why transmission is at high voltage, which of two resistors dissipates more in series and in parallel, and why a fuse melts.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
State the equation for the power dissipated in a resistor in terms of potential difference and resistance.
Numbers
A current of 3.0 A flows through an 8.0 Ω resistor for 2.0 minutes. Calculate the energy dissipated.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the equation for the power dissipated in a resistor in terms of current and resistance, and define every symbol.
Model answer
The equation is P = I²R, where P is the power in watts, I the current in amperes and R the resistance in ohms.
- 2
Show how P = I²R follows from P = VI.
Model answer
For a resistor V = IR, so substituting into P = VI gives P = (IR)I = I²R.
- 3
State the equation for the power dissipated in a resistor in terms of potential difference and resistance.
Model answer
The power is P = V²/R, obtained by substituting I = V/R into P = VI, where V is in volts and R in ohms.
- 4
Calculate the power dissipated when a current of 2.0 A flows through a 15 Ω resistor.
Model answer
The power is P = I²R = 2.0² × 15 = 60 W, and 60 W ÷ 2.0 A gives 30 V, which is indeed 2.0 A × 15 Ω, confirming the result.
- 5
Calculate the power dissipated in a 6.0 Ω resistor with a potential difference of 12 V across it.
Model answer
The power is P = V²/R = 144 ÷ 6.0 = 24 W, and the current is 2.0 A so P = VI = 12 × 2.0 = 24 W, confirming the result.
- 6
A heater is rated at 1.2 kW when connected to a 230 V supply. Calculate the resistance of its element.
Model answer
The resistance is R = V²/P = 52 900 ÷ 1200 = 44 Ω, and 230² ÷ 44.1 returns 1.2 × 10³ W as a check.
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