^Coefficient of coupling (K)

It is defined as,

(A) The value of K is 0 < K < 1 for loose coupling (i.e. When the axis of two coils are parallel to each other & on different lines )

(B) K = 1 for tight coupling ( i.e. when two coils are wound on each other).

(C) When the axis of two coils are ⊥ to each other & on different lines K = 0 & this case is called zero coupling.