Two circuits have a coefficient of mutual induction of $0.09 \ H$. The average $e.m.f.$ induced in the secondary circuit due to a change of current from $0 \ A$ to $20 \ A$ in $0.006 \ s$ in the primary circuit will be:

$A$ small square loop of wire of side $l$ is placed inside a large square loop of side $L$ $(L \gg l)$. If the loops are coplanar and their centres coincide,the mutual inductance of the system is directly proportional to :

Two planar concentric rings of metal wire having radii $r_1$ and $r_2$ $(r_1 > r_2)$ are placed in air. The current $I$ is flowing through the coil of larger radius. The mutual inductance between the coils is given by ($\mu_0 =$ permeability of free space).

Derive the formula for mutual inductance of two very long coaxial solenoids. Also,discuss the reciprocity theorem.

Find the mutual inductance in the arrangement,when a small circular loop of wire of radius $R$ is placed inside a large square loop of wire of side $L$ $(L \gg R)$. The loops are coplanar and their centres coincide:

In an induction coil,the secondary $e.m.f.$ is