| for a two-terminal element or a two-terminal circuit with terminals A and B, product of the voltage between the terminals and the electric current i in the element or circuit
where is the line integral of the electric field strength from A to B, and where the electric current in the element or circuit is taken positive if its direction is from A to B and negative if its direction is from B to A
Note 1 to entry: The direction of electric current is as defined in 131-11-29.
Note 2 to entry: In circuit theory the electric field strength is generally irrotational and thus , where and are the electric potentials at terminals A and B, respectively.
Note 3 to entry: The coherent SI unit of instantaneous power is watt, W.