Kirchhoff's Voltage Law (KVL) is another fundamental principle in electrical engineering, introduced by physicist Gustav Robert Kirchhoff. This law is rooted in the principle of energy conservation, which states that energy can neither be created nor destroyed, only transferred or converted from one form to another.

KVL states that the algebraic sum of all voltages around a closed path or loop within a circuit is zero. This means that the total voltage supplied in a loop is equal to the total voltage drop across the components in that loop.

The direction of the loop around the circuit could be clockwise or anticlockwise and can start from any point. Once the loop direction is chosen, positive voltages are those where the negative terminal is encountered first, and negative voltages are those where the positive terminal is encountered first.

By applying KVL in the clockwise direction and rearranging the terms, there is an alternative form of the law: the sum of voltage drops across the components in a loop equals the sum of supplied voltages.

Consider, for example, a household lighting system where three LED lights connected in series are strung together. Each light requires three volts to turn on. By applying KVL, we can determine the voltage needed for the battery to power these lights. The battery voltage equals the sum of the voltage drop across the three lights, which is nine volts.

However, for KVL to hold true, a crucial condition must be met: a circuit cannot contain two different voltages in parallel unless they are equal. This is because, in a parallel connection, the same voltage is applied across all components, and any discrepancy would violate the law of energy conservation.