Ohm's Law The linear relation between voltage, current, and resistance — V = IR — that is fundamental to circuit analysis.
Maxwell's Equations The four equations that unify electricity and magnetism and predict electromagnetic waves traveling at the speed of light.
Three-Phase Electric Power Why the world's power grids use three phases: constant power delivery, rotating fields, and cheaper conductors.
Kirchhoff's Circuit Laws The two conservation laws that govern every electrical circuit: current conservation at nodes and voltage conservation around loops.