KIRCHHOFF’S VOLTAGE LAW

The sum of all the voltages, as you go around a circuit from some fixed point and return there from the opposite direction, and taking polarity into account, is always zero. At first thought, some people find this strange. Certainly there is voltage in your electric hair dryer, radio, or computer! Yes, there is—between different points in the circuit. However, no single point can have an electrical potential with respect to itself. This is so simple that it’s trivial. A point in a circuit is always shorted out to itself.
What Kirchhoff was saying when he wrote his voltage law is that voltage cannot appear out of nowhere, nor can it vanish. All the potential differences must balance out in any circuit, no matter how complicated and no matter how many branches there are.
Consider the rule you’ve already learned about series circuits: The voltages across all the resistors add up to the supply voltage. However, the polarities of the emfs across the resistors are opposite to that of the battery. This is shown in Fig. 1. It is a subtle thing, but it becomes clear when a series circuit is drawn with all the components, including the battery or other emf source, in line with each other, as in Fig. 1.

Fig. 1. Kirchhoff’s voltage law. The sum of the voltages E + E₁+ E₂ + E₃ + E₄ = 0, taking polarity into account.