Kirchhoff's voltage law
When analyzing electric circuits, two basic laws of electricity are the most useful, Kirchhoff's current law and Kirchhoff's voltage law. These equations often use either the branch method, the loop current method or the nodal method to create a set of linear equations which must be solved to determine all of the voltages and currents in a complex electrical circuit.
Kirchhoff's voltage law can be stated as: "Around any closed loop or path in a circuit, the algebraic sum of all voltage drops must equal zero. In other words, energy is conserved."
Introductory Electronics for Scientists and Engineers, Second Edition, by Robert E. Simpson, Allyn and Bacon, Inc. 1987.