KIRCHHOFF'S VOLTAGE LAW BASIC INFORMATION AND TUTORIALS

Kirchhoff’s voltage law (often abbreviated KVL) states that the sum of voltages around any closed loop in a circuit must be zero. In essence, this law expresses the basic properties that are inherent in the definition of the term “voltage” or “electric potential.”

Specifically, it means that we can definitively associate a potential with a particular point that does not depend on the path by which a charge might get there. 

This also implies that if there are three points (A, B, and C) and we know the potential differences between two pairings (between A and B and between B and C), this determines the third relationship (between A and C).

Without thinking in such abstract and general terms, we apply this principle when we move from one point to another along a circuit by adding the potential differences or voltages along the way, so as to express the cumulative voltage between the initial and final point.

Finally, when we go all the way around a closed loop, the initial and final point are the same, and therefore must be at the same potential: a zero difference in all.

The analogy of flowing water comes in handy. Here, the voltage at any given point corresponds to the elevation. A closed loop of an electric circuit corresponds to a closed system like a water fountain. The voltage “rise” is a power source—say, a battery—that corresponds to the pump.

From the top of the fountain, the water then flows down, maybe from one ledge to another, losing elevation along the way and ending up again at the bottom. Analogously, the electric current flows “down” in voltage, maybe across several distinct steps or resistors, to finish at the “bottom” end of the battery.

This notion is illustrated by in the simple circuit in Figure 2.4 that includes one battery and two resistors. Note that it is irrelevant which point we choose to label as the “zero” potential: no matter what the starting point,adding all the potential gains and drops encountered throughout the complete loop will give a zero net gain.