Series vs Parallel Explorer
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About this MicroSim
The same two LEDs and the same two 220 Ω resistors, wired two different ways. Switch between them with the dropdown and watch what changes: in series both LEDs are dim and share one small current; in parallel both are bright and the battery has to supply twice as much.
The Circuit
Power always arrives on the top rails and is jumpered down to the bottom rails, so the only thing that changes between the two modes is the topology itself.
Series — one loop, crossing the center channel partway through:
T+ rail → a5 → R1 220Ω → D1 → across the channel (e12 → f12)
→ R2 220Ω → D2 → B− rail
Parallel — two independent branches, one in each half of the board:
T+ rail → a5 → R1 220Ω → D1 → T− rail
B+ rail → j5 → R2 220Ω → D2 → B− rail
| Component | Value | Purpose |
|---|---|---|
| BAT | 3–9 V, slider | supply |
| R1, R2 | 220 Ω | one current-limiting resistor per LED |
| D1, D2 | red | identical, so any difference comes from the wiring |
The numbers at 6 V
Series: the two LEDs drop 1.9 V each, leaving 2.2 V across 440 Ω of resistance. Every part carries 4.7 mA, and so does the battery.
Parallel: each branch sees the full 6 V, so each carries (6 − 1.9) / 235 ≈ 17.4 mA — and the battery supplies 34.9 mA, the sum of the two.
That is a seven-fold difference in supply current from nothing but rewiring.
How to Use It
- Press Start, then read the three numbers under the board.
- Switch the dropdown to Parallel and watch all three change.
- Move the Supply voltage slider in each mode. In series the LEDs go dark below about 4 V; in parallel they stay lit much lower. Ask why.
What the Animation Shows
Dot speed on each wire is proportional to the current in that wire, so the parallel branches visibly move dots faster than the series loop. In parallel, the wire feeding the two branches carries both branch currents — watch it run faster than either branch.
The red rail jumper carries no current in series mode and shows no dots. It is still correct to leave it in place, which is worth pointing out: a wire with no current is not a wasted wire.
Lesson Plan
Grade Level, Subject and Topic
Middle school and high school. Electronics. Series and parallel topology, Kirchhoff's current law.
Learning Objective
Students will be able to predict how total current changes when identical loads are rewired from series to parallel, by comparing branch current with supply current in both configurations.
Activities
Predict, then switch
Before touching the dropdown, ask: if we move from series to parallel, does the battery supply more current, less, or the same? Most students say "the same" or "less". Then switch.
Verify Kirchhoff
In parallel mode, read D1, D2 and the battery. Confirm that the battery current is exactly the sum. Then ask what the battery current would be with a third identical branch.
Find the cliff
In series mode, lower the supply until the LEDs go out. Two LEDs need 3.8 V before any current flows at all. Ask students to predict that voltage from the forward-voltage figures before they find it with the slider.
Assessment
- In series mode, D1 reads 4.7 mA. What does D2 read, and how do you know without looking?
- You add a third LED and resistor in parallel. What happens to the battery current?
- Why does the series circuit stop working below about 4 V while the parallel one keeps going?
Model Limitations
This simulation solves the circuit in DC steady state. It does not model transient behavior, capacitance, inductance, AC, diode I-V curves, or transistor gain. Component values are ideal — no tolerance, no temperature effects, and no wire resistance.
References
- Push Button and LED Circuit — the same parts in a simpler single-branch circuit
- Solderless Breadboard Layout — how rows, columns and rails are connected