Kirchhoff's Laws of Electrical Network

Before the two laws themselves can be stated precisely, three words that describe the LAYOUT of a circuit need fixed meanings, because Kirchhoff's laws are written in terms of exactly these three things.

A junction (also called a node) is any point in a circuit where two or more conductors meet. It is the place where current arriving along one wire can split into several wires, or where current arriving along several wires can combine into one.

A loop, or mesh, is any closed conducting path within the network -- start at some point, follow a chain of conductors, and return to the same starting point without retracing any wire.

A branch is any single part of the network that runs between exactly two junctions, without passing through any other junction along the way. A branch may contain just one resistor, several resistors, a cell, or any combination of circuit elements, but electrically it behaves as one path carrying one well-defined current.

A simple network with only two junctions, joined by three separate branches (three distinct paths connecting the same two points), already illustrates all three ideas together: the two junctions are the only points where current can split or combine; each of the three paths between them is one branch, carrying its own branch current; and any two of the three branches, taken together, form one closed loop. …