Kirchhoff's voltage law states that the algebraic sum of all voltages around any closed path must equal zero. Stated another way, the sum of the voltage drops equals the applied voltage.
Kirchhoff's current law states that the algebraic sum of all currents directed in and out of any point in a circuit must equal zero. Stated another way, the current into a point equals the current out of that point.
A closed path is a loop. The method of using algebraic equations for the voltages around the loops to calculate the branch currents is illustrated in Fig. 9–5.
A principal node is a branch point where currents divide or combine. The method of using algebraic equations for the currents at a node to calculate the node voltage is illustrated in Fig. 9–7.
A mesh is the simplest possible loop. A mesh current is assumed to flow around the mesh without branching. The method of using algebraic equations for the voltages around the meshes to calculate the mesh currents is illustrated in Fig. 9–8.
