Both alternating current and direct current are measured in ampere. But how is ampere defined for alternating current? It cannot be defined from two mutual attraction of two parallel wires carrying ac current, as dc current is defined. My guess is that since an ac current changes direction with the source frequency and attractive force would average to zero, the ac current should be defined of some property that is independent of direction of current. Also, there is one ampere of RMS value of alternating current in a circuit if the current produces same average heating effect as one ampere of dc current would produce under same condition.
[Physics] How is ampere defined for alternating current
electric-currentelectromagnetism
Best Answer
I think you are correct. Joule's heating effect is such a property which is used to define 1Amp for AC source as it does not depend on the direction of current. Over a full cycle the average current supplied by an AC source is zero.