Page 312 - Basic Electrical Engineering

We have, therefore, chosen I as the reference phasor. Voltage drop across the
resistance and the current flowing through it are in phase. This is because, as
we have seen earlier that in a resistive circuit, voltage and current are in

phase. The current flowing through an inductor lags the voltage across it by
90°. That is to say, voltage drop across L, i.e., V will lead the current by
L
90°. Again V = IX and X = ωL. The vector sum of V and V is equal to
L
R
L
L
L
V. The angle between V and I is called the power factor angle ϕ. Power factor
is cosϕ. Considering the triangle ABC we can express

or,

or,

where

Z is called the impedance of the total circuit. Triangle ABC in Fig. 3.18 (b) is

also called the impendance triangle which is redrawn as in Fig. 3.19. From
the impedance triangle