Inductors in series and parallel

Inductors in series and parallel combine mathematically the same way resistors do, but for a completely different physical reason. In series, the same current flows through each coil, so their magnetic fields add and the inductances add. In parallel, each coil carries part of the total current, so the total inductance divides just as resistance does in a parallel network.

However, this simple math only works when the inductors’ magnetic fields do not interact. If inductors are placed close together, their fields couple and the effective inductance changes. In that case, the series/parallel formulas no longer apply. Simply wiring several inductors in parallel and placing them side‑by‑side will not give the expected result unless the coils are magnetically shielded or spaced far apart.

We will study mutual induction and transformers later, where coils are intentionally placed within each other’s magnetic fields. For now, remember that while capacitors can often be mixed and matched to obtain a desired value, inductors require more care because their magnetic fields can interact in ways that change the total inductance.