The mutual inductance of two coils is $45 \ mH$. The self-inductance of the coils are $L_1 = 75 \ mH$ and $L_2 = 48 \ mH$. The coefficient of coupling between the two coils is

$A$ 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 coils $P$ and $Q$ are separated by some distance. When a current of $3\, A$ flows through coil $P$,a magnetic flux of $10^{-3}\, Wb$ passes through $Q$. No current is passed through $Q$. When no current passes through $P$ and a current of $2\, A$ passes through $Q$,the flux through $P$ is:

$A$ small coil of radius $r$ is placed at the centre of a large coil of radius $R$,where $R >> r$. The coils are coplanar. The coefficient of mutual inductance between the coils is

The induction coil works on the principle of

Two circular coils of radii $r_1$ and $r_2$ $(r_1 \ll r_2)$ are placed coaxially with their centers coinciding. The mutual inductance of the arrangement is