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 For example, if VR and VC
are voltages across R and C, respectively in an RC circuit, then the
total voltage across RC combination is 
2
2
RC
R
C
V
V
V
=
+
 and not
VR + VC since VC is p/2 out of phase of VR