Circuit analysis refers to characterizing the current flowing through and voltage across every circuit element within a given circuit. Some general rules apply when analyzing any circuit with any number of elements. However, before discussing this rules, we need to define other terms that are commonly used in circuit analysis literature: a node and a branch.
A node is the connecting point of two (or more) elements of a circuit.
A branch represents a circuit element that is located between any two nodes in a circuit.
Russian scientist Gustav Robert Kirchhoff (1824–1887) introduced the two laws that now bear his name. These laws allow the calculation of currents and voltages in electric circuits with multiple loops using simple algebraic equations. Kirchhoff’s current law (KCL) states that the net current entering a node in a circuit is zero.
Some currents enter into a node and some leave the node. Thus, based on this law, the sum of the currents entering a node is equal to the sum of the currents leaving that node. KCL results from the law of the conservation of charge.
