In node-voltage analysis, we write equations and eventually solve for the node voltages. Once the node voltages have been found, it is relatively easy to find the current, voltage, and power for each element in the circuit. For example, suppose that we know the values of the node voltages and we want to find the voltage acrossR3 with its positive reference on the left-hand side. To avoid additional labels in Figure 2.16, we have made a second drawing of the circuit, which is shown in Figure 2.17. The node voltages and the voltage vx across R3 are shown in Figure 2.17, where we have used arrows to indicate reference polarities. (Recall that the positive reference is at the head of the arrow.) Notice that v2, vx, and v3 are the
voltages encountered in traveling around the closed path through R4, R3, and R5. Thus, these voltages must obey Kirchhoff’s voltage law. Traveling around the loop