Thus, the ac ampere must be defined in terms of some property
that is independent of the direction of the current Joule heating
is such a property, and there is one ampere of rms value of
alternating current in a circuit if the current produces the same
average heating effect as one ampere of dc current would produce
under the same conditions 5 In an ac circuit, while adding voltages across different elements, one
should take care of their phases properly