Hi,

I have a question regarding the formula for electrical power, P=IV

I understand the mathematics of how the formula was derived, but I can't grasp why it works. It was my understanding that current was simply a measure of the number of coulombs of charge flowing past one point in one second. Contrarily, voltage is a measure of the potential energy of the coulombs, energy which will not be converted into other forms until the charge in question goes from the negative to positive terminal of the circuit (although we can say that if there is a load, there will hardly be any potential energy after the load).

In the case of a light bulb, how then can we say that P=IV? Even if we assume that the voltage is "used up" inside the filament, we don't know how many coulombs are moving past the filament per second; we only know the amperage for some imaginary point.

Any help in understanding this better would be much appreciated. While I am relatively confident that I could handle the formula itself, I feel that I am cheating myself if I don't get the full background story.

Thanks,
raspu3000