Two coils of self-inductances $6 mH$ and $8 mH$ are connected in series and are adjusted for the highest coefficient of coupling. The equivalent self-inductance $L$ for the assembly is approximately: (in $mH$)

Two identical induction coils,each of inductance $L$,are joined in series and placed very close to each other such that the winding direction of one is exactly opposite to that of the other. What is the net inductance?

Two coils with self-inductance $1 H$ and $3 H$ are connected in series. Their mutual inductance is $5 H$. The equivalent self-inductance of the combination is: (in $H$)

Three coils of inductance $L_1 = 2 \ H$, $L_2 = 3 \ H$, and $L_3 = 6 \ H$ are connected such that they are separated from each other. To obtain an effective inductance of $18/11 \ H$ between points $A$ and $B$, which of the following figures is correct?

Three coils of inductance $L_1 = 2 \ H$, $L_2 = 3 \ H$, and $L_3 = 6 \ H$ are connected such that they are separated from each other. To obtain an effective inductance of $1 \ H$, which of the following combinations, as shown in the figure, is correct?

The inductance between $A$ and $D$ is