
12 Inductors and inductance
/(common)
Diagram 14
V
R
to obtain V. The reason for this is that in the inductive part of the
circuit the common current / is out of phase with V
L
and in the resistive
part / is in phase with V
R
. V
L
and V
R
can only, therefore, be added
graphically (or by phasors) as in Diagram 14.
By construction we can see that V
R
is in phase with / and V
L
is 90°
out of phase with /, and that the resultant is the applied voltage V. θ° is
the number of degrees that / lags behind the applied voltage V.
From Diagram 14 it can be seen that the triangle abc is right-angled,
having ab = V\ be = V
L
and ac = V
R
. Hence by Pythagoras' theorem ...