Parallel Circuit Simulator — Description
What you see on screen
The circuit is drawn in a lab-notebook style on warm cream paper with ruled lines. Two vertical bus bars run down the left and right sides of the canvas, connected at the top and bottom by horizontal wires, forming the outer loop. Three horizontal branches stretch across the middle, each carrying one resistor — R₁ (blue), R₂ (red), R₃ (green). The battery sits on the left bus bar, and a switch sits on the right bus bar.
Components
The battery shows its EMF voltage and three glowing cell segments. Each resistor is drawn as a box with a classic zigzag symbol inside, labelled with its name above and resistance value below. When the circuit is on, each resistor also shows its individual branch current in milliamps. The switch pivots open or closed and glows amber when closed.
When the switch is closed
The wires darken to ink-black and glow slightly. Coloured electron particles flow along each branch independently — blue particles through R₁, red through R₂, green through R₃, amber particles along the outer bus. Branches with lower resistance carry faster-moving particles, visually showing higher current. A dashed amber arrow on the right annotates that the same voltage appears across every branch. All four meters update live — total current, equivalent resistance, voltage, and power.
Key physics shown
Every branch shares the same voltage regardless of its resistance. Each branch carries a different current determined by its own resistance alone. The total current drawn from the battery is the sum of all three branch currents. The equivalent resistance is always smaller than the smallest individual resistor.
Suggested Class Activities
Activity 1 — Spot the Difference (Starter, 10 min) Open both the series and parallel simulators side by side. Ask students to write down three things that look different about how the circuits are drawn, before touching any controls. This primes them to notice bus bars, branching, and independent paths before the physics is introduced.
Activity 2 — The Equal Voltage Rule (Guided, 15 min) Set EMF to 12V. Change R₁ to 50Ω, R₂ to 200Ω, R₃ to 400Ω. Ask students to read the voltage shown on each resistor. Then change R₃ to 10Ω and repeat. The voltage never changes. Students record their observations and write one sentence explaining why — leading to the rule that voltage is the same across all parallel branches.
Activity 3 — Current Races (Guided, 15 min) Keep EMF fixed at 12V. Watch the particle speeds in each branch. Ask students to predict which branch will have the fastest particles before adjusting resistors. Set R₁ = 500Ω, R₂ = 100Ω, R₃ = 50Ω and observe. Students calculate expected branch currents by hand (I = V/R) then verify against the values shown on screen.
Activity 4 — The Equivalent Resistance Puzzle (Investigation, 20 min) Students set all three resistors to the same value (e.g., 150Ω each) and record the equivalent resistance shown. They then halve one resistor and record again. Challenge: can they predict the equivalent resistance before changing any slider? They use the formula 1/Req = 1/R₁ + 1/R₂ + 1/R₃ and check their answer against the badge. The key discovery — Req is always less than any single branch — often surprises students.
Activity 5 — Power Station (Extension, 20 min) Students are given a challenge: the total power drawn must stay between 400mW and 500mW using a 12V battery. They must find a combination of R₁, R₂, and R₃ that meets the target. They record their solution and then find a second combination. This builds fluency with P = V²/Req and reinforces that multiple configurations can produce the same outcome.
Activity 6 — Broken Branch (Discussion, 10 min) Ask students: what happens if one branch is removed from a parallel circuit — does the whole circuit stop? Simulate this by dragging one resistor to its maximum value (500Ω, approximating a very high resistance). Observe that the other branches continue flowing. Contrast this with the series simulator where opening the switch stops everything. This directly addresses a common misconception and connects to real-world wiring in homes.
Activity 7 — Design a Lighting Circuit (Homework or Project) Students design a home lighting circuit on paper using what they have learned. They must choose resistor values that keep each bulb’s current below a safe threshold, calculate the total current drawn, and explain why parallel wiring is used in homes rather than series. They can use the simulator to test their design before finalising it.