How to reason about a circuit.

A handful of rules let you work out the voltages and currents anywhere in a circuit before you build anything.

1. 1Series & parallelSeries shares current and splits voltage; parallel shares voltage and splits current. Combining resistors, capacitors, and inductors in both arrangements.1 min read·4 questions
2. 2Kirchhoff’s lawsCurrent in equals current out at any node, and voltages around any loop sum to zero. The two rules that let you solve a circuit no shortcut covers.1 min read·3 questions
3. 3Voltage & current dividersInteractiveThe divider equation, why loading changes the answer, and how to pick divider resistances that are neither too noisy nor too wasteful.1 min read·3 questions
4. 4The RC time constantInteractiveτ = R × C sets how fast a capacitor charges. The 63% rule, five time constants to settle, and how it governs delays, debouncing, and filters.1 min read·3 questions
5. 5Impedance, filters & resonanceImpedance is resistance that depends on frequency. How R, L and C combine into low-pass, high-pass and band-pass filters, and what resonance does.1 min read·2 questions