Kirchoff's law states that, the potential difference along a closed circuit must be ZERO. Now, lets do a simple question 1. We have a simple circuit consists of INDUCTOR and Voltage source-->V=V.sin(wt) At any instant, why must the voltage supplied equal the voltage generated in the inductor? (this is written in many textbooks) Can the voltage supplied exceed the voltage of inductor and hence we have a NON_ZERO potential difference along a closed loop? Now, simple question 2. Suppose we have a capacitor which has been charged. Next, we connect the 2 plates of the capacitor by a ZERO RESISTANCE wire. The capacitor will take a very short time to neutralise itself. In this very short time, we can see that, the potential difference is not zero along a close loop, because the resistence is zero. So, after these 2 examples, I would like to ask, what GUARNTEE kirchoff's law of potential difference? Thanks, Twukwuw.