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 inductors,each of inductance $L$,are connected in parallel. One more inductor of value $5 \text{ mH}$ is connected in series with this configuration,and the effective inductance is $15 \text{ mH}$. The value of $L$ is . . . . . . $\text{mH}$.

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?

$A$ circuit contains two inductors of self-inductance $L_1$ and $L_2$ connected in series as shown in the figure. If $M$ is the mutual inductance between them,then the effective inductance of the circuit will be

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?

Two inductors of $80 \ mH$ each are joined in parallel. The current passing through the combination is $2.1 \ A$. The energy stored in this combination of inductors is