Ask where a path can split
Two resistors are in series when they lie on one unbranched path. The same current passes through both. They are in parallel when each is connected across the same two electrical points. Those branches have the same voltage across them; their currents can differ.
A circuit drawing can be bent or rearranged without changing these relationships. A junction is a real electrical connection. Two lines merely passing close together are not automatically a junction. Before calculating, identify the points that are connected and count the possible paths between them.
Try two 6 Ω resistors on 6 V
In series, add the resistances: 6 + 6 = 12 Ω. Ohm’s law gives source current I = V ÷ R = 6 ÷ 12 = 0.5 A. Each resistor drops 0.5 × 6 = 3 V. The drops add to the source’s 6 V.
In parallel, add the reciprocals: 1/R = 1/6 + 1/6, giving 3 Ω overall. Each branch has the full 6 V and carries 6 ÷ 6 = 1 A. The source supplies both branch currents, so its total is 2 A. It is the arrangement, not the number of parts, that changed the source current.
What is shared, and what is not?
“Parallel means equal currents” works only for branches with the same resistance under these assumptions. Change the second resistor to 12 Ω: on a 6 V parallel supply the first branch still carries 1 A, while the second carries 0.5 A. The shared quantity is voltage.
Likewise, equal voltage drops in the series example came from equal resistances. A 6 Ω and a 12 Ω resistor in series share the same current, but the 12 Ω part takes twice the voltage drop. Use the structure first, then the component values.
Build a prediction for Spark Island
When a mission asks for a particular connection, describe the path before running it: “both parts are on one route” or “each branch joins the same two points.” Then compare the game’s component feedback with your prediction. Trace actual terminals; a tidy rectangle alone proves nothing.
This calculator uses fixed, linear resistors. Spark Island also includes components whose behaviour depends on polarity, settings or state. Real filament bulbs change resistance as they heat, and real sources can sag or limit current. Do not treat these ideal numbers as guaranteed readings or brightness levels for those parts. Keep experiments in the browser.
Source & scope
OpenStax: Resistors in Series and Parallel. Reference for the connection rules and resistance relationships. The worked values and calculator are this article’s own teaching example.
This is an Aurism learning article, with AI-assisted development as described in our editorial approach. It does not claim an independent expert review or that a simplified model reproduces every game outcome. Report a correction.
TRY THE IDEA IN A GAME
Spark Island
Use the mission’s actual instructions and feedback to test your next prediction.