(6 13), the induced emf is given by
(
B)
–d
d
N
t
Φ
ε =
d
–
d
I
L
t
ε =
(6 14)
Thus, the self-induced emf always opposes any change  (increase or
decrease) of current in the coil It is possible to calculate the self-inductance for circuits with simple
geometries