Electrical Engineering ⇒ Topic : Main points of phase

The following points may be noted carefully :

• The phase of an alternating quantity (voltage or current) depends upon the instant from which the time is measured. Thus in Fig. (a), the time is measured from the instant the voltage is zero. Had the time been measured from the instant the voltage was positive maximum, the phase of maximum positive value would have been zero.
• An alternating quantity (voltage or current) is completely known if we know its (a) maximum value (b) frequency and (c) phase.

In electrical engineering, we are more concerned with relative phases or phase difference between different alternating quantities rather than with their absolute values

                                                     figure (a)