The principle underlying kirchhoff’s voltage law KVL is that no energy is lost or created in an electric circuit; in circuit terms, the sum of all voltages associated with sources must equal the sum of the load voltages, so that the net voltage around a closed circuit is zero.
The principles of conservation of energy imply that the directed sum of the electrical potential differences (voltage) around any closed circuit is zero.
The second method of circuit analysis discussed in this chapter employs mesh currents as the independent variables. The idea is to write the appropriate number of independent equations, using mesh currents as the independent variables. Subsequent application of Kirchhoff’s voltage law around each mesh provides the desired system of equations.
In the mesh current method, we observe that a current flowing through a resistor in a specified direction defines the polarity of the voltage across the resistor , and that the sum of the voltages around a closed circuit must equal zero, by KVL. Once a convention is established regarding the direction of current flow around a mesh, simple application of KVL provides the desired equation.
The number of equations one obtains by this technique is equal to the number of meshes in the circuit. All branch currents and voltages may subsequently be obtained from the mesh currents, as will presently be shown. Since meshes are easily identified in a circuit, this method provides a very efficient and systematic procedure for the analysis of electric circuits. The following box outlines the procedure used in applying the mesh current method to a linear circuit.
In mesh analysis, it is important to be consistent in choosing the direction of current flow. To avoid confusion in writing the circuit equations, unknown mesh currents are defined exclusively clockwise when we are using this method. To illustrate the mesh current method,