17.3 Phase of A.C.

17.3 Phase of A.C.

The angle $\theta$ which specifies the instantaneous value of the alternating voltage or current is called the phase. The instantaneous values of voltage and current are given by $V = V_{o} \sin\omega t$ or $V = V_{o} \sin\theta$ $I = I_{o} \sin\omega t$ or $I = I_{o} \sin\theta$ The angle which gives the value of alternating quantity is known as phase. The phase of points A, B, C, D and E are $0$, $\pi/2$, $\pi$, $3\pi/2$ and $2\pi$ respectively as shown in Fig. 17.5(a), Thus each point of A.C cycle corresponds to a phase.

(Fig. 17.5: (a) AC cycle corresponds to a phase.)