An introduction to series and parallel connections — the second piece of basic circuit theory you need to understand how logic gates are built.

With two resistors we establish the defining property of each arrangement: components in series share the same current (while their voltage drops differ by Ohm's law), and components in parallel share the same voltage (while their currents differ). Swapping the resistors for switches turns this into a question of continuity — is there an unbroken path between two points? Two switches in series give a path only when BOTH are closed (logical AND); two switches in parallel give a path when EITHER is closed (logical OR). Because a transistor is just a controllable switch, this series = AND / parallel = OR mapping is exactly how transistors are wired together to build logic gates.

Chapters:
0:00 Introduction — why series and parallel matter
0:27 Series resistors: same current, different voltage drops
1:35 Parallel resistors: same voltage across each
1:56 From resistors to switches; defining nodes A and B
2:20 Series switches and the meaning of continuity
2:55 Series = AND: continuity only if both switches are closed
3:34 Parallel switches
4:07 Parallel = OR: continuity if either switch is closed
4:31 Wrap-up: configuring transistors into logic gates

Part of the Digital Logic course / Infobook:
https://bigmikeprojects.github.io/digital-...