Chapter 22 · Physics module 13
Circuits
Read the symbols. Follow the circuit.
Explore eight focused lessons on symbols, current, voltage, resistance, circuit connections, power and calculus. Change the models, work through examples and check your understanding.
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Change an input. Discover a relationship.
Chapter Overview
Symbols, current, voltage, resistance, resistivity, series and parallel, and power.
Each lesson brings the key relationships, a model you can control, assumptions, worked examples and a five-question quiz together. Lesson quiz answers remain in the open page only.
Learning Objectives
- Recognise and draw standard circuit symbols
- Explain current and potential difference
- Apply Ohm’s law with its conditions
- Compare series and parallel connections
- Calculate resistance, power and transferred energy
Explore the Eight Lessons
Follow the sequence or select the idea you need.
Circuit Symbols & Diagrams
Read and draw circuits with standard symbols, and place meters correctly.
Learn · Explore · Practise →02I = ΔQ/ΔtElectric Current & Charge
Define current as the rate of charge flow and follow the conventional direction.
Learn · Explore · Practise →03V = W/QVoltage & Potential Difference
Measure the energy carried per coulomb between two points of a circuit.
Learn · Explore · Practise →04V = IRResistance & Ohm's Law
Define resistance, read I–V graphs, and state when Ohm’s law applies.
Learn · Explore · Practise →05R = ρL/AResistivity
Separate the material property from the wire’s length and cross-section.
Learn · Explore · Practise →06Rₛ = R₁ + R₂Series & Parallel Circuits
Combine resistors and predict how current and voltage are shared.
Learn · Explore · Practise →07P = VIElectric Power
Rate energy transfer with P = VI and cost it over time.
Learn · Explore · Practise →08I = dQ/dtCurrent Calculus
Read current as a gradient and recover charge and energy as areas under a graph.
Extend with calculus →Interactive Circuit Builder
Add lamps and resistors, compare series and parallel connections, and open or close the switch to inspect ideal meter readings.
Equivalent load resistance12 Ω
Supply current0 A
Voltage across load 10 V
Load 1 · current / power0 A / 0 W
Guided builder: add up to four loads, then choose a series chain or parallel branches. Readings update immediately. With the switch open, the voltage across a connected load is 0 V; the supply voltage is across the switch. Lamps use fixed resistance here, so their colour indicates current, not a calibrated brightness. Use this on-screen model only; real circuit ratings and hazards are not simulated.
Guided ideal DC circuits with zero-resistance wires, an ideal supply and meters. Lamps are modelled as fixed resistances; a real filament warms up and changes resistance. Never test meter-placement faults on a real supply.
Open the full circuit-symbols lesson →Key Relationships
- Current
- I = ΔQ/Δt
- Potential difference
- V = W/Q
- Ohm’s law
- V = IR
- Uniform wire
- R = ρL/A
- Series resistance
- R = R₁ + R₂ + …
- Electrical power
- P = VI
Check the assumptions and units in each lesson before applying a formula.