Kirchoff's voltage law
Kirchoff's voltage law (KVL) states that that the change in potential difference (in other words, the voltage drops) in any closed electrical circuit must sum to 0. A voltage drop is the change in voltage over any element in a circuit.
KVL is derived from the fact that the voltage at any point in the circuit must have one single value. For example, say you start at point A and travel around the loop adding up voltages along the way. If the voltage drops did not sum to zero, then when you returned to point A it would have a different voltage than when you started, which is impossible.
- See also: Kirchoff's current law