Fig. 1,228—Pressure and current curves illustrating the term "in phase." The current is said to be in phase with the pressure when it neither lags nor leads.
When there is phase difference, as between current and pressure, they are said to be "out of phase" the phase difference being measured as in fig. 1,229 by the angle φ.
Fig. 1,229—Pressure and current curves illustrating the term "out of phase." The current is said to be out of phase with the pressure when it either lags or leads, that is when the current is not in synchronism with the pressure. In practice the current and pressure are nearly always out of phase.
When the phase difference is 90° as in fig. 1,231 or 1,232, the two alternating quantities are said to be in quadrature; when it is 180°, as in fig. 1,233, they are said to be in opposition.
When they are in quadrature, one is at a maximum when the other is at zero; when they are in opposition, one reaches a positive maximum when the other reaches a negative minimum, being at each instant opposite in sign.
Ques. What is a departure from synchronism called?
Ans. Loss of synchronism.
