In the explanation that follows, the symbols V and I are used to mean peak a.c. values (Figure 26.1) of alternating signals. Root mean square (r.m.s.) values are represented by Vrms and I rms; that is, I Irms / 2 . The symbols v and i represent instantaneous values of a.c. signals and V and I will have their usual meaning of d.c. values. So, we may write v V sin (2πft).