What law explains why electric current is the same at every point in a simple series circuit?

Kirchhoff’s current law explains why current is the same at every point in a simple series circuit.

The law states that the algebraic sum of currents entering a circuit junction equals the sum leaving it. This follows from conservation of electric charge: charge does not accumulate indefinitely at an ideal junction. In a series circuit, every component lies on one uninterrupted path, so the current entering each component must equal the current leaving it.

German physicist Gustav Kirchhoff published his circuit laws in 1845. His other law, Kirchhoff’s voltage law, concerns the sum of potential differences around a closed loop rather than currents at a junction.

The rule changes in a parallel circuit. There, current divides among branches, while the total current entering the junction equals the sum of the branch currents. Conventional current direction is used in circuit calculations, even though electrons in metals move oppositely.