impedance

A Bell Labs film in which Dr. J.N. Shive uses a mechanical wave machine to demonstrate reflection, standing waves, resonance and impedance matching. He includes some equations but relies mostly on real-world examples a layperson can follow.

Rick Hartley's AltiumLive keynote on differential pairs in PC boards. He argues the rules from cables and twisted pairs do not carry over, and covers which pair geometry gives the best impedance control, the right spacing, routing practice and how much skew is acceptable.

AlphaPhoenix uses a custom high-speed measurement setup to watch voltage waves travel down wires and split at a fork. It answers how electricity knows where to go and how quickly that process happens.