Thus, the circuit is a purely inductive ac circuit Let
the voltage across the source be v = vm sinw t Using
the Kirchhoff’s loop rule, 
∑ε ( )t =
0 , and  since there
is no resistor in the circuit,
d
0
d
i
v
L
t
−
=
(7 10)
where the second term is the self-induced Faraday
emf in the inductor; and L is the self-inductance of
FIGURE 7